ATDEPARTMENT
OF HEALTH AND HUMAN SERVICES
FOOD AND DRUG ADMINISTRATION
CENTER FOR DRUG EVALUATION AND
RESEARCH
ANTI-INFECTIVE DRUGS ADVISORY
COMMITTEE (AIDAC) MEETING
Wednesday, March 5, 2003
9:00 a.m.
Marriott Washingtonian Center
Grand Ballroom
975 Washington Boulevard
Gaithersburg, Maryland
PARTICIPANTS
James E.
Leggett, Jr., M.D., Acting Chair
Tara P.
Turner, Pharm.D., Executive Secretary
MEMBERS
David M. Bell, M.D.
Alan S. Cross, M.D.
Mary P. Glode, M.D.
Celia J. Maxwell, M.D.
Jan E. Patterson, M.D.
Ellen Wald, M.D.
ACTING
INDUSTRY REPRESENTATIVE (NON-VOTING)
Kenneth R. Brown, M.D.
CONSULTANTS
John S. Bradley, M.D.
James H. Jorgensen, Ph.D.
Donald M. Poretz, M.D.
Michael Proschan, Ph.D.
L. Barth Reller, M.D.
Keith A. Rodvold, Pharm.D.
Maria H. Sjogren, M.D.
GUEST
SPEAKER (NON-VOTING)
Francis Tally, M.D.
FDA
Renata Albrecht, M.D.
Edward Cox, M.D., M.P.H.
Mark Goldberger, M.D., M.P.H.
John Powers, M.D.
Janice Soreth, M.D.
C O N T E N T S
PAGE
Call to
Order:
James E. Leggett, Jr., M.D. 4
Introduction
of Committee 4
Conflict
of Interest Statement:
Tara P. Turner, Pharm.D. 6
Opening
Comments:
Mark Goldberger, M.D., M.P.H.
9
Linkages
of Resistance Determinants in Bacteria:
17
James H. Jorgensen, Ph.D.
Questions
from Committee 41
Industry
Perspective on List of Pathogens:
Francis P. Tally, M.D. 51
Questions
from Committee 69
List of
Pathogens of Public Health Importance:
John H. Powers, M.D. 76
Questions
from Committee 116
Open
Public Hearing:
Dr. Jerome Schentag 175
Dr. Richard Gesser 179
How
Clinicians Use data for Clinical
Decision
Making:
John Bradley, M.D. 182
Relating
Clinical Data from One Disease to Another:
Edward Cox, M.D., M.P.H. 195
Committee
Discussion 211
Summary 291
P R
O C E E D I N G S
Call to Order
DR.
LEGGETT: Good morning. I would like to welcome everyone for today's
March 5th's meeting of the Anti-Infective Drugs Advisory Committee.
A
little housekeeping since it is now 9 o'clock, committee members, you have a
little green menu in front of you. That
menu needs to be filled out and passed to Tara, so we can get it in by 9:30 if
you want to have lunch. Lunch will be
served next-door in Salon D today, but we will need your menus.
Can
we begin the day by having everyone introduce themselves. I guess I will start down at that corner.
Introduction of Committee
DR.
GOLDBERGER: Mark Goldberger from the
Office of Drug Evaluation IV, FDA.
DR.
COX: Ed Cox, Deputy Director, Office of
Drug Evaluation IV, FDA.
DR.
SORETH: Good morning. I am Janice Soreth. I am the Division Director for
Anti-Infectives.
DR.
ALBRECHT: Hello. I am Renata Albrecht, Director of Division of
Special Pathogen and Immunologic Drug Products.
DR.
PORETZ: I am Don Poretz in private
practice of infectious disease in Fairfax, Virginia.
DR.
PATTERSON: Jan Patterson, Medicine-
Infectious Diseases, University of Texas Health Science Center, San Antonio.
DR.
RODVOLD: Keith Rodvold, University of
Illinois at Chicago.
DR.
TURNER: Tara Turner, Executive Secretary
for the committee.
DR.
LEGGETT: Jim Leggett, Infectious
Diseases, Oregon Health Sciences University and Providence Portland Medical
Center.
DR.
WALD: Ellen Wald, Pediatric Infectious
Diseases, University of Pittsburgh School of Medicine.
DR.
GLODE: Mimi Glode, Pediatric Infectious
Disease, Children's Hospital, University of Colorado.
DR.
BRADLEY: John Bradley, Pediatric
Infectious Diseases, Children's Hospital, San Diego.
DR.
RELLER: Barth Reller, Infectious
Diseases, Director of Clinical Microbiology, Duke University.
DR.
CROSS: Alan Cross, Infectious Diseases,
Center for Vaccine Development at the University of Maryland.
DR.
BELL: David Bell, National Center for
Infectious Diseases at the CDC in Atlanta.
DR.
JORGENSEN: Good morning. I am Jim Jorgensen from the University of
Texas Health Science Center.
DR.
PROSCHAN: I am Mike Proschan from the
National Heart, Lung, and Blood Institute.
DR.
BROWN: Ken Brown, Infectious Disease,
University of Pennsylvania, representing industry.
DR.
LEGGETT: Welcome, everyone.
Now,
Dr. Turner, could you read the conflict of interest statement, please.
Conflict of Interest Statement
DR. TURNER: The following announcement addresses the
issue of conflict of interest with respect to this meeting and is made a part
of the record to preclude even the appearance of such at this meeting.
The
topics of today's meeting are issues of broad applicability. Unlike issues before a committee in which a
particular product is discussed, issues of broader applicability involve many
industrial sponsors and academic institutions.
All
special Government employees and Federal participants have been screened for
their financial interests as they may apply to the general topics at hand. The
following participants have reported no current financial interests with regards
to pharmaceutical companies: Drs. Mary
Glode, David Bell, and Michael Proschan.
Dr.
Donald Poretz has reported a financial interest in a pharmaceutical company
covered under CFR 2640.202(b) deminimus exemption.
The
following participants have reported interests in pharmaceutical companies and
the Food and Drug Administration has granted general matters waivers to the
following SGEs which permits them to participate in today's discussions: Drs. James Leggett, Ellen Wald, Alan Cross,
Celia Maxwell, Jan Patterson, John Bradley, Donald Poretz, L. Barth Reller,
Judith O'Fallon, James Jorgensen, and Keith Rodvold.
A
copy of the waiver statements may be obtained by submitting a written request
to the Agency's Freedom of Information Office, Room 12A-30 of the Parklawn
Building.
Because
general topics impact so many institutions, it is not prudent to recite all
potential conflicts of interest as they apply to each member and consultant.
FDA
acknowledges that there may be potential conflicts of interest, but because of
the general nature of the discussion before the committee, these potential
conflicts are mitigated.
With
respect to FDA's invited speakers, there are reported interests which we
believe should be made public to allow the participants to objectively evaluate
their comments. Dr. Francis Tally is
Chief, Scientific Officer, at Cubist Pharmaceuticals. Dr. Tally also owns stock in Cubist.
In
addition, we would like to disclose that Dr. Kenneth Brown is participating in
this meeting as an acting industry representative, acting on behalf of
regulated industry. Dr. Brown owns stock
in Merck and in his rollover retirement account he owns shares in Pfizer,
Genentech, and Johnson & Johnson, as of December 31, 2002. Dr. Brown also serves as a consultant to
Wyeth and Merck and works one to four days per month.
In
the event that the discussions involve any other products or firms not already
on the agenda for which FDA participants have a financial interest, the
participants involvement and their exclusion will be noted for the record.
With
respect to all other participants, we ask in the interest of fairness that they
address any current or previous financial involvement with any firm whose
product they may wish to comment upon.
Thank
you.
DR.
LEGGETT: Thank you.
Dr.
Goldberger, could you please provide us with some opening comments.
Opening Comments
DR.
GOLDBERGER: Yes. I would like to welcome everybody to the
second day of this advisory committee.
Yesterday, we had a very interesting discussion focused around a
product. Today, we are going to continue
what has been an ongoing effort stretching over a few years at least and
actually more intensively over the last year or so to look at issues related to
the development of antimicrobial drugs including antimicrobial drugs for
resistant indications.
We
have had a major two-day advisory committee in early February of 2002, another
meeting in the summer, a meeting with IDSA, PhRMA, and ourselves this past
fall, and now today's meeting to talk about a variety of issues that we hope
will lead to encouraging the development of new antimicrobial drugs and to also
thinking about ways that we can really facilitate that approach, encourage
companies by perhaps reducing the overall amount of resources that are necessary,
but at the same time, at the end of the day, get information that is at least
is of high quality, if not higher quality, than what we have been accustomed to
in the past.
Today's
meeting is going to focus on two issues that have come up as part of some of
these meetings. One issue could be
summarized briefly by referring to it as the list, that is, the list of
microbial organisms, and today really we are concentrating on bacterial
organisms that are of public health interest for which we should really be
encouraging the development of drugs.
Again,
the organisms on this list generally tend, in fact, to be those that have
demonstrated some level of resistance to therapies that have been commonly used
to, for instance, treat.
We
have had some discussions about this.
Industry has expressed a great interest in having a little more in the
way of something defined as to what organisms we believe are important, so that
they can look carefully to decide whether or not these things I think represent
appropriate opportunities for them.
We
are certainly in agreement that providing guidance to industry about these
things is useful. On the other hand, a
list per se, simply making up a lot of organisms does require one to then be
thinking about updating it, you know, on a regular basis, and one of the things
we want to talk about today is how one sort of decides the kind of things that
ought to be on some list, what are the parameters that are appropriate, so that
the list can be dynamic and yet not overly burdensome in terms of thinking
about what ought to be on it, and more to the point, if we can define some
parameters, then that gives industry a little more flexibility.
Should
a new issue come up, industry will not be in the position of looking to see is
this on the list, is this not on the list.
They will be able to use parameters that have been discussed and defined
to make an argument about why such organisms are appropriate targets for
antimicrobial drug development.
So,
that is going to occupy discussion I think most of the morning, and we have
several presenters who will be talking about this issue. We hope to have a fair amount of committee
discussion.
In
the afternoon, we are going to talk about another topic that we hope will lead
to more expedited drug development, and that is sort of looking at the overall
package that many companies submit as part of, you know, development of a new
antimicrobial.
As
most of you are probably aware, it is uncommon although not by any stretch
unheard of for a new antibacterial drug to come in for a single
indication. Generally speaking, drugs
come in for a variety of indications.
To
give you a good example, fluoroquinolones is one example, as well as some
macrolides, often will come in for a variety of respiratory indications, in
part because from a purely business point of view, it makes much more sense to
have this package when you are trying to get drugs on formulary, so when you
can promote them of having related indications, and in some cases, the breadth
of indications will be even broader.
There
will be respiratory indications, sometimes intra-abdominal indications, skin,
complicated skin, et cetera, so the packages can be fairly large.
In
general, multiple studies have been submitted for each of these
indications. There are--and we will be
talking about this, this afternoon--clear exceptions to the idea that you need
multiple studies for each indication.
One
of the things we really want to talk about is can we advance the model as to
how indications could support one another to a point where it will facilitate
overall development by perhaps reducing the size of a development program, and
at the same time will provide a rational approach both to the general issues of
development over a broad range of indications and to the related and very
important issue that companies have addressed with us in meetings on a
one-on-one basis, et cetera, I think has come up at open meetings like this, as
well as, we want to get an indication for a resistant organism.
Sometimes
it is difficult to acquire adequate numbers of those organisms from a study or
studies in a single body site, what is the latitude, how much pooling across
body sites can be done. As you can see,
that is related to the overall issue of how indications support one another.
We
think this is an important issue. We
think from a practical point of view, and I go back to the years that I have
spent in practice, that clinicians are prepared to make inferences as to how a
drug is likely to perform based on how it performs in other settings, and I
certainly think that a drug that one feels more comfortable--this is my own
personal opinion--about how a drug will perform in a seriously ill patient if
there is already data suggesting that in other serious illnesses or infections,
the drug has performed well.
I
think that at times, although as a clinician we are comfortable doing that,
from a regulatory point of view, we don't clearly have that laid out as to how
that might occur, and I think that that is an area that is worth talking about
in some detail, talking about the parameters that might help us in deciding
what indications could support one another, so that we can put out some
guidance that will be helpful to industry in thinking about what a package might
look like.
So,
in any case, we are going to have some
discussion about this in the afternoon with the hope of again facilitating
antimicrobial drug development, as well as development for resistant
indications, and we hope that at the end of day, that we will have enough ideas
here that will assist us in writing some guidance that will be helpful to
industry.
There
has been a great desire, not surprisingly, and this goes across many areas in
FDA and far outside anti-infectives, for industry to get some type of guidance
as to how to proceed since they are much more comfortable, they can sit and
look at what is required or suggested as opposed to having to depend on
individual interactions, et cetera, although there is always an issue about
getting guidances done because of the amount of people you have available to
sit and write them.
Here,
we actually have a somewhat different issue, which is not always quite as
common. I actually believe one of the
obstacles to writing some of the guidances, particularly what I was speaking
about for the afternoon, how indications support one another, is that there are
unresolved scientific questions about how far one can really go.
The
one thing you learn about, you know, when you are writing a guidance or when you
are writing a letter to a company, et cetera, if you are not really clear what
it is you can do, what it is you are trying to say, what you actually write
will turn out to be, you know, really kind of semi-disastrous or at least not
useful.
So,
before we embark on trying to get some sort of draft guidance out for comment,
we would like to see how far we can get in resolving some of the underlying
issues, so that everybody at least understands those issues, and then it is
simply a matter of taking that and trying to put it into some clear English.
That
in and of itself is no small achievement, but at least you understand what it
is you think you trying to say, so that's what our goals are for today. Again, we don't expect this to be the end of
this process.
We
expect to continue to have meetings like this, hopefully, another meeting, as
well, with IDSA, PhRMA, et cetera, just to continue talking about these issues
and to work through the variety of scientific issues that we think we need to
do, but we are hopeful at the end of today, we will be a little closer to being
able to provide the advice we would like to.
Thank
you.
DR.
LEGGETT: Thank you.
John,
could I ask you to introduce yourself.
DR.
POWERS: John Powers, Lead Medical
Officer for Antimicrobial Drug Development in 04.
DR.
LEGGETT: Thank you.
The
first speaker of the day will be Jim Jorgensen who is going to talk to us about
linkages of resistance determinants in bacteria.
Linkages of Resistance Determinants in Bacteria
James H. Jorgensen, Ph.D.
DR.
JORGENSEN: Good morning, everyone.
I
seem to have failed the first test and that is how to run the laptop computer
up here.
[Slide.]
What
I would like to speak with you about this morning is about antibiotic
resistance and the era that we find ourselves in, in emerging resistance among
a number of very common hospital-acquired and also now community-acquired
bacterial pathogens.
I
think everybody recognizes that we are in this very unusual era that none of us
have ever seen or lived through before, and that is the era of emerging or
evolving antibiotic resistance.
As
you can see on the upper part of my slide, some would argue that this is really
the era of emerging acronyms as we find new names for all of these different
resistant organisms.
I
think what is clear as we talk about VRE, VISA, and VRSA is that these
organisms are of clinical significance and are becoming more frequent, and we
have relatively few therapeutic options today.
Certainly,
these organisms compromise the utility of some of our most important compounds,
such as the extended spectrum cephalosporins, the macrolides, as well as the
fluoroquinolones.
Certainly,
the obvious need that will be discussed today is exactly which organisms are of
greatest importance and where do we need help in developing new compounds.
Now,
what I have been asked to talk about specifically is this concept that I would
call "associated resistance."
That is some of the resistance mechanisms possessed by these organisms
affect multiple members of the same class or family or subclass.
That
is, for example, beta-lactam resistance in staph affects not only the
semisynthetic penicillins, but also the cephalosporins and the
carbapenems. But the second thing is
those resistance mechanisms that may be genetically linked, that may be on the
same plasmid or on the same transposon and are therefore transferred in mass
from one strain to another.
The
latter part of that is the fact that there are some frequently associated
resistance mechanisms that are not co-transferred in the sense of being truly
linked in the same cassette, but simply are very frequently found in the same
clones or same derivatives of clones.
[Slide.]
I
think everybody has seen these data and I wanted to start here because it
illustrates our point that in the era of the '90s, we went from almost no VRE
in the United States or essentially case reports of VRE to, by the end of the
'90s, about 1 out of 4 enterococcal isolates were vancomycin resistant. I could have used other examples, but I
thought VRE would be a very good place to begin.
[Slide.]
VRE
also illustrates the problem, that in the United States, almost all of our VREs
occur in Enterococcus faecium. Inherent
in most strains of Enterococcus faecium is also penicillin, ampicillin, and,
for that matter, carbapenem resistance.
Now,
these are not genetically linked events, but they are present in the background
of that species. Many of these isolates
also produce inactivating enzymes that affect multiple aminoglycosides, so most
of these have high-level aminoglycoside resistance.
Despite
the fact that we do have some newer antibiotics that have proven very useful in
therapy of VRE infections, we already have experienced resistance developing
during therapy with some of the newer agents including linezolid and
quinupristin-dalfopristin. So, it also
illustrates the point of not putting all of our eggs in one basket, I believe.
[Slide.]
Now,
this is a partial list and a lot of these organisms are where I want to delve a
little bit deeper in the next few minutes.
For
example, the last organism, Enterococcus faecium, as I mentioned, most of the
time, probably 90 percent of isolates produce a low-affinity,
penicillin-binding protein that provides resistance, not only to penicillin,
but to other relevant beta-lactams.
I am
going to spend a few minutes talking about methicillin-resistant staph and then
I think there are some new things that are worthy of consideration, but
methicillin-resistant staph or resistant to multiple members of that same major
class, the beta-lactams.
Then,
I think extended spectrum beta-lactamases are a significant problem, and I
believe they will become more frequent in the near future, and these enzymes
have hydrolytic activity against all of the current penicillins, true cephalosporins, and also aztreonam.
Then,
I will say a few words about resistance in Strep pneumoniae including emerging
fluoroquinolone resistance.
[Slide.]
To
begin with, MRSA, I think there are some new things here. MRSA have been around for a long time, and I
think it is noteworthy that within about a year or so of the introduction of
methicillin for clinical use, the first strain was recognized in the United
Kingdom that was resistant to methicillin.
In
the 1960s, there were some hospital outbreaks in Europe and the UK and
certainly in the 1970s in this country.
From the 1970s until today, I think you are all aware MRSA have become a
major problem of health care institutions.
Now,
one point I would like to make at this point is that these conventional MRSA or
healthcare-associated MRSA strains have been multidrug resistant. Here, I mean in addition to other
beta-lactams, other drug classes.
[Slide.]
However,
what is new and I believe rapidly emerging is community-acquired MRSA and that
probably most of us first heard about this in Detroit among the injection drug
users in that city in 1980 and '81, in which MRSA was quite prevalent among
that population.
But
then in the early '90s, community-acquired MRSA was described in Western
Australia and also in New Zealand, and what was different about these strains
and what should have raised our awareness was that these were not multidrug
resistant strains. For the most part,
they were resistant only to penicillin and oxacillin.
Then,
the CDC reported four children in the '90s in the upper Midwest who had very
serious community-acquired MRSA infections, and once again, these were not
conventional hospital-acquired MRSA isolates.
The
CDC has also done a great deal of work along with several state health
departments to characterize community onset MRSA in Native American populations
in Alaska, Minnesota, and also the State of Washington.
Also,
I think during this period, MRSA has become a very frequent cause of skin
infections in incarcerated individuals, both in penitentiaries and in
jails. Then, in the San Francisco Bay
area of California, workers there have described that among the homeless
populations, skin infections due to these community-acquired strains of MRSA
have become quite frequent.
[Slide.]
What
this means I guess is we need a new definition of MRSA or a new subdefinition
and what the CDC is currently using is healthcare-associated MRSA, and that
means to many of us the hospital-acquired strains that we are most familiar
with.
These
are patients who have recently been in the hospital where they acquired their
strain or perhaps they have been in a rehab center or they have undergone or
continue to undergo hemodialysis, or perhaps it has been communicated to them
directly by a home or other healthcare worker.
However,
we need some new definitions for these community strains, and I have used the
term "community-acquired now a few times.
CDC prefers the term "community-onset" meaning that the
infection originates in the community, and it may have been through some
conventional risk factor, such as recent antibiotic use or perhaps a
hospitalization, not recently, but in the distant past, and prolonged
colonization, but there is still a number of patients who do not have any of
the conventional risk factors, illustrating that this organism now does appear
to be a true community-acquired pathogen.
[Slide.]
Now,
there are several differences between the healthcare-associated and
community-onset isolates, and they include the fact that I have already stated,
the healthcare-associated strains usually are resistant to multiple drug
classes.
Usually,
this includes macrolides and lincosamides, usually aminoglycosides and also
fluoroquinolones. In contrast, the
community-acquired strains usually are only resistant to penicillin and
oxacillin although some strains now are resistant also to macrolides and some
to fluoroquinolones, but this is not predictable, this is not in most cases the
majority of strains.
As I
will show you a second, they contain a different version of the mec element, a
much smaller element and much more easily transmitted among the
community-acquired isolates.
These
strains in the hospital usually do not have this toxin called Panton-Valentine
leukocidin, whereas, the community-acquired strains usually produce this. At least the currently feeling is that PVL
explains why these strains are so prone to cause skin or subcutaneous
infections and also severe necrotizing pneumonia.
Also,
these strains often produce as many, well,
I should say as many as 19 different toxins or superantigens including
staphylococcal, enterotoxins, possibly toxic shock toxin I.
[Slide.]
So,
these strains phenotypically look different and they have, as I said, a
different staphylococcal chromosomal cassette of SCCmec variety. Now, there are four types and, in fact, Type
IV is now being subdivided.
What
I want to show you, and I use this slide very reluctantly, is that the Type I
is now considered an archaic version,
and that is, it is not found in most current MRSA isolates.
Type
II and Type III, which are found in the healthcare-associated isolates, are
really very large and often carry with them transposons that code for other
antibiotic resistance including macrolides, lincosamides, and also
aminoglycoside-modifying enzymes.
So,
that SCCmec Type II or III, I think helps explain the MDR phenotype of the
healthcare-associated strains. What is
different is the Type IV is a much smaller piece of DNA, in fact, some would
argue small enough to fit in the head of a phage and perhaps be transmitted
through transduction.
This
Type IV mec cassette does not include any of those transposons for multidrug
resistance, so it appears that that is a transferable element that is now
finding its way into very fit community-acquired clones of Staph aureus and
contains only the essential information for methicillin or oxacillin
resistance.
[Slide.]
Now,
one of the things that is sometimes challenged is this concept that we should
view MRSA as resistant to all beta-lactams, and I am aware that there are some
beta-lactams under development that have high affinity for this PBP-2A or
altered special penicillin-binding protein of methicillin-resistant
staphylococci.
However,
I decided to go back to the origin, and that is, one of the first studies that
helped to illustrate that beta-lactams, even if they appear active in vitro, do
not provide adequate therapy in vivo.
This
was a paper by Jacques Acar in Paris, published in Antimicrobial Agents in Chemotherapy
in the early '70s. Illustrated in that
early experience with MRSA in France, physicians did try to use cephalosporins
to treat patients who were bacteremic or who had endocarditis, and when used
alone, and these were cephalothin or cephaloridine, both agents that I think
have among the best activities against staphylococci of all of the
cephalosporins, what you find is that very few patients were cleared of their
bacteremia using a cephalosporin alone, and if you added to it an
aminoglycoside, you did somewhat better, but it was not really very successful
therapy.
Recall
that these strains did have aminoglycoside resistance determinants. When you looked at endocarditis, even though
the number of patients was very small, these patients' bacteremias could not be
cleared using either a cephalosporin or an aminoglycoside alone.
Now,
certainly there are more modern data than this, but I thought it might be
useful to go back to the beginning just for a moment.
[Slide.]
Now,
other resistance mechanisms that are commonly found or co-transferred in these
healthcare-associated strains, as I have alluded to, include the macrolide and
lincosamide determinants. They may be
ermA or more frequently ermC, and they may be either constitutively produced or
they may be inducible.
This
TN554, which is commonly found in the SCCmec Types II or III, codes for this
kind of resistance, and is co-transferred with methicillin resistance.
Aminoglycoside-inactivating
enzymes can be produced by these organisms including this important so-called
bifunctional enzyme which has both an acetylating and phosphorylating end or
activity, and is the same enzyme found in many enterococci that have high-level
aminoglycoside resistance.
Then,
most of these healthcare-associated strains today are resistant to
fluoroquinolones either because of gyrase A mutations or because they have an
active efflux pump that removes the drugs from the cells.
Then,
they may have the ribosomal protection mechanism of tetM for tetracycline
resistance or they may have an efflux pump that removes most members of that
class.
[Slide.]
The
other problem, however, that I think is more urgent and of greater concern is
the fact that in this background of MRSA, we have seen either diminished
susceptibility to vancomycin in the form of VISA or vancomycin-intermediate
Staph aureus, in which about 8 times as much vancomycin is required to inhibit
these strains as a normal strain, or recently, in 2002, in the U.S., we have
seen the first true VRSA isolates.
Both
of those isolates contain the vanA gene sequences from Enterococcus, and in the
first case, the patient in Michigan, it was fairly clear that that was
transferred from vancomycin-resistant Enterococcus faecalis, not faecium.
[Slide.]
Now,
let me shift gears and talk for a moment about gram-negatives and about
extended spectrum beta-lactamases. Most
of the ESBLs that we are familiar with in North America are derivatives from
either the TEM-1 or SHV-1 enzymes.
These
are the beta-lactamases ordinarily found in E. coli and Klebsiella that
generally just code for ampicillin resistance, but when mutations occur, they
may then hydrolyze at least at high inoculum all of the currently available
penicillins, cephalosporins, and aztreonam.
As
you can see on this slide, as of last Friday, there were a huge number of
different TEM and SHV enzymes that have a different molecular structure or a
different spectrum of activity. In fact,
some of these strains appear susceptible to some cephalosporins, but resistant
to others.
[Slide.]
Now,
the molecular basis for this are point mutations that probably occur
spontaneously in the genes that encode either TEM-1 or SHV-1, and even a 1 or 2
amino acid sequence change can take a strain from being very susceptible to a
drug like ceftazidime to being highly resistant, so these are fairly subtle
point mutations that occur every day.
[Slide.]
Some
of these enzymes provide very obvious resistance to a compound like ceftazidime
as in the case of TEM-10, while retaining very low MICs to cefotaxime, so the
argument has been, well, this is a potential difference between these compounds
that perhaps could be taken advantage of.
[Slide.]
However,
at very high inoculum, that is, if you increase the number of cells, the amount
of enzyme present, you can see even the latest generation cephalosporins are
hydrolyzed by these enzymes.
On
the other hand, the structure of the carbapenems tends to resist hydrolysis by
the ESBL and they tend to remain susceptible to that class.
[Slide.]
Now,
again, clinical significance is very important.
David Paterson from Pittsburgh, I think has done some of the most
important work to illustrate the clinical significance of these strains, and in
a 2001 publication, he reported a multi-country, multi-continent study looking
at Kleb pneumoniae bacteremias, and about 18 percent or so of these organisms
were found to produce ESBLs.
Nine
of those were treated with a cephalosporin that, by conventional testing and
conventional breakpoints, were either intermediate or susceptible to a
cephalosporin, however, among those 9, 3 patients died and 5 required
additional therapy.
Overall,
there were 32 patients that were treated with a cephalosporin that we would,
based on testing of that drug by itself, consider either susceptible or
intermediate to a particular drug. Among
those that were classified as intermediate, all 4 failed therapy and 15 of 28
of the strains considered susceptible, meaning they had fairly low MICs, also
failed therapy.
Among
those were 5 patients treated with cefepime, to illustrate the last point, and
4 of those also failed.
[Slide.]
Now,
ESBL-producing strains carry their gene for beta-lactamase production on a
plasmid, and that plasmid can be easily shared among different isolates of the
same species or between species.
Located
on the same plasmid in most of the ESBL are genes that also code for
trimethoprim sulfa and for gentamicin resistance, so here is an example of
co-transfer of genes that affect more than one class of drug.
Unrelated
to that is the fact that many and I would guess maybe 40 or 50 percent of
isolates also were fluoroquinolone-resistant, but that is not a
plasmid-mediated event in these strains and it is not co-transferred.
[Slide.]
Then,
there are many other gram-negative rods, too many to mention in my limited
time, but I just want to make a brief pitch for the importance of Pseudomonas
aeruginosa and the fact that Pseudomonas isolates may have a number of
different beta-lactamases including the ability to hyperproduce the ampC or
Bush group 1 beta-lactamase to code for resistance to a variety of
beta-lactams, but they may also have plasmid-mediated enzymes, such as PSE-1,
-3, or -4, and also the less common ESBLs, such as the OXA group of enzymes
that are not yet very common in this country, but are in some other parts of
the world.
Many
of these strains produce enzymes that chemically inactivate in aminoglycosides
or they may have outer membrane protein changes which essentially close the
door to penetration by the aminoglycoside group of drugs.
Fluoroquinolone
resistance is now relatively common among Pseudomonas isolates often due to
mutations in the gyrA gene.
Very
interesting I think is this class of efflux pumps, often the Mex B, D, or F
pumps that can be found in Pseudomonas, that every effectively remove
fluoroquinolones and cephalosporins from these strains before they can have any
activity.
[Slide.]
Now,
I will say a few words about pneumococci to wrap up my remarks. First of all, everyone is aware of penicillin
resistance in pneumococci. The point of
this slide, the upper portion at least, is that there are several different
penicillin-binding proteins that can be modified through self-transformation,
that is, taking in DNA from another pneumococcal strain or even from a viridan
strep that might be an oropharyngeal colonizer.
Pneumococci
can then build so-called mosaic genes that code for penicillin-binding proteins
of lower affinity.
For
high-level penicillin resistance, there may need to be as many as 3 of these
penicillin-binding proteins modified, but for cephalosporin resistance, that
is, extended spectrum cephalosporins, it is really only necessary to have 2 of
these PBPs altered.
So,
there are now some strains that are more resistant to cephalosporins than to
penicillin.
[Slide.]
Now,
looking at CDC surveillance data from the active bacterial core surveillance
program published by Cindy Whitney in 2000, I would like to simply illustrate
the point that penicillin-susceptible pneumococci, in this column, are rarely
resistant to other drug classes, that is, they rarely have genes that would
affect the macrolides, tetracycline, or the fluoroquinolones.
As
you move to strains that have diminished susceptibility to penicillin, you see
it is more frequent that those isolates may carry genes for other drug classes,
and as you move to the penicillin-resistant Strep pneumos, it is quite common
to see macrolide resistance, trimethoprim sulfa resistance, and indeed there is
a statistically significant association between penicillin and fluoroquinolone
resistance in these strains.
Now,
that is not because these genes are all co-transferred, but rather these are
clones of pneumococci that have become repositories, if you will, for many
different resistance genes, and the fittest of these clones have now circulated
throughout the world.
[Slide.]
So,
macrolide resistance in the United States is most often coded by a gene called
mefA or mefE, which is an efflux pump. A
smaller number, a small percentage of strains have the erm gene, which codes
for clindamycin, as well as macrolide resistance.
What
is interesting to me is it is the reverse in Europe. The erm strains are much more common than the
efflux strains.
Many
of these strains also have tetM or an efflux pump, and many of the strains now,
particularly the pen-resistant ones, have altered enzymes needed in the folate
pathway that affect trimethoprim or sulfa or both to code for trimeth sulfa
resistance.
[Slide.]
Quinolone
resistance in pneumococci has become a major concern. The study published in 2002 by Davies and
colleagues looked at strains that had borderline susceptibility to
levofloxacin, but found that about 4.5 percent of these strains actually
contain a first-step mutation of the parC locus that would code for higher MICs
to drugs like ciprofloxacin, but not so much so for levo.
The
second step or double mutants, on the other hand, become quite obviously
resistant to the currently used fluoroquinolones, and those are estimated
between 0.2 and 0.5 percent of strains in the U.S., so a very small percentage
as of today.
However,
when those mutations occur, as we have showed in this earlier study, those
mutations, particularly those that involve both the parC and gyrA loci, also
are the same targets used by the later, more potent fluoroquinolones and raise
the MICs of those compounds, as well.
So,
the concern here is that despite the greater potency of the newer
fluoroquinolones, they still affect the same drug targets.
[Slide.]
Now,
I think the real concern and where we ought to look is the data that have
emanated from Hong Kong and have been published by Ho and colleagues, in which
they showed in 1995, a very small percentage of their pneumococci were
fluoroquinolone resistant, essentially, the same as we currently see in the
United States.
However,
a few years later, that percentage had increased and then by 2000, it was more
than 13 percent of all of their isolates, and if they looked specifically at
the more resistant clones, that is, the penicillin-resistant strains, it was
more than one-fourth of those.
Now,
what is unique here is that this is a single clone or, if you will, single
strain of pneumococcus that has been shared throughout patients in Hong Kong,
so it is not dissemination of genes in the sense of transmissible elements, but
rather a single, very fit clone that originated originally from Spain and is a
serotype 23F clone, has now become very common in that area of the world.
So,
the concern I think is could we see this sort of thing in North America.
[Slide.]
Now,
my final slide is maybe food for thought more than firm data. That is, Elaine Tuomanen and colleagues in
Memphis have illustrated a few strains, one at least associated with a
meningitis treatment failure in a 10-month-old that they describe as being
tolerant to the bacteriocidal effect of vancomycin and also the bacteriocidal
effect of beta-lactam antibiotics.
This
child had recurrent meningitis after a full course of both cefotaxime and vanc
therapy. They have been working to
identify a particular gene associated with this defect, but this is a totally
different aspect of a failure of the autolytic system of this strain or these
strains which is triggered by both the beta-lactams and vancomycin.
So,
this is I think a point of concern, but it as yet a fully clarified area.
So,
those are my feelings on this and I guess I would say the reasons for this are
that there are mechanisms that we recognize that affect closely related
compounds, such as the beta-lactams with MRSA.
Also,
there are mechanisms, some of which I have described, that are co-transferred,
that are genetically tied together and go with one gene into a different
strain.
Lastly,
as I attempted to illustrate with pneumococci, there may be multidrug resistant
strains due to the fact that there are clones that over time have collected
these resistance genes and maintain them for fitness in an environment of
antibiotic use.
So,
with that, I think I will conclude and I appreciate your attention.
Mr.
Chairman, do we have questions?
Questions from Committee
DR.
LEGGETT: Yes. Why don't we open it up for questions.
I
have a quick one, I may have missed it.
The vanco tolerance, was it pneumococci?
DR.
JORGENSEN: Yes.
DR.
LEGGETT: Jan.
DR.
PATTERSON: Jim, would you like to
comment on the linkage of resistance in Acinetobacter, multidrug-resistant
Acinetobacter?
DR.
JORGENSEN: Acinetobacters certainly can
be multidrug resistant including penicillin, cephalosporins, and can acquire
resistance to carbapenems, and I think that has been the concern, is that some
of those strains, because of resistance to other classes, have been treated
with carbapenems only to later become carbapenem resistant.
DR.
LEGGETT: Don.
DR.
PORETZ: In our hospital, the tertiary
care facility, MRSA continues, we still continue to be active with the sulfa
trimethoprim, 80 percent of MRSA sensitive to sulfa trimethoprim, doxycycline,
minacycline still very, very active yet. Those particular drugs are completely
worthless against E. coli, Strep pyogenes.
Is
it just because those drugs have not been used that often in the hospital in
the past or why do we continue to have 80 percent sensitivity with sulfa and
semisynthetic tetracyclines?
DR.
JORGENSEN: I think that's a good question. The vancomycin intermediate and
vancomycin-resistant Staph aureus strains have all been susceptible to trimeth
sulfa and would seem even to be perhaps the drug of choice for those strains in
terms of a good susceptibility profile.
Many
MRSAs are susceptible to minacycline and perhaps the reason for that is
minacycline is not so well pumped by the tetracycline efflux pump that many of
those strains have.
I
think you are right about the potential utility of those agents against those
strains, but not against the gram-negatives, and I am not sure I can explain
why except that organisms like E. coli and other gram-negatives are part of our
normal GI flora and are exposed every day to any antibiotic we would take for
any reason and perhaps that is a partial explanation.
DR.
LEGGETT: John.
DR.
BRADLEY: I think the complicated nature
of resistance, the multiple mechanisms of resistance, the ability of organisms
to develop new resistances highlight something that we have been talking about
on a number of occasions, about the difficulty in assigning a drug approval for
an organism resistant to one particular drug, and that as your presentation
really predicts for the future, that the situation is going to get far more
complicated than simple and not only will we have to deal with Strep pneumo
that is resistant to penicillin, cefuroxime, clarithromycin, et cetera, but we
are going to have to deal with pseudomonads that have multiple drug
resistances, acinetobacter, and are we going to be needing to deal with drug
approvals for drugs that are active against each and every one of those
antibiotics that are resistant on your list, requiring that the sponsor produce
treatment successes for each of those sets of resistances.
So,
you have done a beautiful job of painting the future for us.
DR.
JORGENSEN: I wish it were more
optimistic.
DR.
LEGGETT: Barth.
DR.
RELLER: Jim, your presentation raises
many questions that I have. I will
restrict it, if I might, to two.
First,
you mentioned the development unequivocally of resistance while on therapy with
linezolid, quinupristin-dalfopristin where if one did PFGE, it is clearly the
same organism.
Of
these mechanisms of resistance, and time wouldn't permit all of them, which
ones are recognized, of the more common ones, to develop on therapy and which
ones has that not been observed? For
example, my understanding is with penicillinase with Staph aureus, going way
back, that on long-term observations that the development or acquisition of
that plasmid in vivo doesn't occur.
But
what about these other mechanisms, and the importance of it is where one might
be on secure ground with a susceptible organism at the initiation of therapy,
but see it change right under your eyes.
DR.
JORGENSEN: Enterobacter.
DR.
RELLER: Well, Enterobacter, the
D-repression with this is enough, but are any of the others, is there a
pitfall, is it actually even more complicated than what you say having to do
with you think you are okay, but then the ground shifts even in the course of
therapy of an individual patient?
DR.
JORGENSEN: I think you are right with
penicillin-resistant or I should say penicillin-susceptible Staphylococci. In order to become penicillin-resistant, your
organism would have to go out and find the plasmid and the beta-lactamase gene
somewhere else, so it is not likely to change during therapy.
In
the case of the Bush Group I or ampC beta-lactamase, you have an enzyme present
in virtually every isolate of Enterobacter, Citrobacter freundii, Serratia
marcescens, et cetera, that is just sitting there waiting to have a mutation in
its represser sequences to a very high level of resistance. So, that can occur in maybe a couple of days
during therapy.
VRSA
represents acquisition of a gene group again from outside, so it is not likely
to happen commonly. It had to go and
find that gene in the right environment of those two patients.
VISA,
on the other hand, represents acclimatization to the presence of vancomycin
over a long period of time, this thickened cell wall that is developed and been
described in these strains, which seems to be an adaptation to the pounding
away of that strain by vancomycin over a period.
So,
I think in many cases, these are genes that are acquired, transferred, et
cetera, or may be kept by a strain when spontaneous mutations occur, such as in
the case of ESBL, that those spontaneous mutations do not have value in an
environment that is not saturated with antibiotics, so we see those strains
mostly in intensive care unit patients where there is value to maintaining
those mutations for production of a very high potency beta-lactamase.
DR.
RELLER: The second question that is
related is with the different cassettes with Staphylococcus aureus MRSA,
hospital-associated community-associated, is there a difference in the common
detection mechanisms used in laboratories, salt screen plate, latex
agglutination, PCR for mecA, are there differences in the ability to detect
accurately methicillin resistance among these strains?
The
analogy is with the resistance and the use of cephalosporins, in other words,
are there pitfalls in detection that are related to the different cassettes?
DR.
JORGENSEN: Well, first of all, all of
the variants of MRSA contain the mecA gene whether there is a big piece of DNA
that goes along with it or a small piece, so genetic tests, such as PCR, that
detect the presence of the mecA gene would pick all of those up very
effectively.
All
of those code for PBP-2a, so tests that would detect the protein product of
mecA also would be positive with all of those.
I
think some of the hospital-acquired strains are more likely to have the
heterogeneous expression of oxacillin resistance that is more difficult to
detect by phenotypic tests, such as distifusion or MIC.
The
detection, however, is somewhat compromised I think in the community-acquired
strains because microbiologists have been trained to look for multidrug
resistance as a secondary key that a strain might be an MRSA. Even some of our instrument systems have been
programmed with expert systems to look for resistance to aminoglycosides,
tetracycline, et cetera, as a marker for MRSA.
So,
I guess I worry a little bit that the community-acquired strains might be
underappreciated because they don't have that additional red flag that I'm an
MRSA.
DR.
LEGGETT: Celia.
DR.
MAXWELL: Excellent summary, Dr.
Jorgensen.
I
have two questions on your next to the last slide with the 10-month-old and the
meningitis. Was it Strep pneumo, the
organism?
DR.
JORGENSEN: Yes.
DR.
MAXWELL: An earlier slide, looking at
the differences between healthcare-associated and community-associated MRSA,
was the outcome in those patients that were treated or what was the outcome?
DR.
JORGENSEN: Well, in the
community-associated or community-onset isolates, many of these patients had
skin or subcutaneous infections, boils especially. Many of these were severe enough that they
didn't improve without surgical drainage.
As long as they were drained surgically, the limited data, and the data
are not extensive, seemed to suggest it didn't really make a lot of difference
which antibiotic was used.
On
the other hand, if you used an effective antibiotic without surgical drainage,
they didn't do all that well. There are
some groups, such as some of the physicians who manage jail and prison
settings, that favor use of either trimeth sulfa or doxycycline or clindamycin
to treat those strains, but the limited data suggest they make very bad
subcutaneous infections that may require surgical drainage.
DR.
LEGGETT: Dr. Jorgensen, could you
comment upon the growing data about cross-linkage between detergents and
antibiotic resistance?
DR.
JORGENSEN: Well, I can tell you that in
two of the mec cassettes, there are genes for resistance to heavy metals like
mercury and things of that sort, and may also have to do with iodine and other
disinfectants, but that is all I could comment on.
DR.
LEGGETT: John.
DR.
BRADLEY: Just a quick extra piece of
information on that 10-month-old with Pneumococcal meningitis because it
created quite a stir in the pediatric community, and Dr. Tuomanen has done
beautiful molecular diagnostic dissection of the resistance mechanisms. This is an autolysin-resistant, a deficient
organism.
Normally,
with pneumococcus, once you hit it with an antibiotic and cripple it, it kills
itself. Well, this organism won't kill
itself and there is no antibiotic, not vancomycin, not beta-lactams, not
fluoroquinolones, nothing that will kill this organism. It can prevent it from growing, so
antibiotics are static, but you need more than a static agent in the central
nervous system.
So,
the implication isn't just for vancomycin resistance, but it's for resistance
across all antibiotic classes for this organism, and we are just thankful that
it hasn't seemed to have spread outside of Memphis or continued to increase in
its prevalence there. Is that correct?
DR.
JORGENSEN: Yes.
DR.
LEGGETT: Thank you, Dr. Jorgensen.
The
next speaker will be Frank Tally, who is going to give us an industry
perspective on a list of pathogens.
From
the first speech, it looks like the list of pathogens is all our common
pathogens is all I can say.
Industry Perspective on List of Pathogens
Francis P. Tally, M.D.
DR.
TALLY: Mark Goldberger set the stage for
today's meeting with the two major themes of what is the list and do we need,
can one particular study in one system support studies in another system, but I
think in the documentation that was sent out via the Internet, there was also a
third issue I saw in there, is the problem of decreasing research in the area
of developing new antimicrobial agents, and I would like to kind of wind that
into the discussion today.
[Slide.]
Why
develop drug for resistant pathogens?
Well, as you have heard,
resistant pathogens kill people, and I will delve into some of that data. It was nicely discussed by Dick Wenzel at the
November workshop meeting that we have talked about.
For
a pharmaceutical company or a biotech company, one has to justify the
expenditure of a large amount of money to develop a drug for a particular area,
so that drug should have specific advantages which allow the drug to penetrate
into the marketplace and return the investment that the company has made.
An
alternative, which I spoke about at sessions a couple years ago, if we are not
going to do that, then, one should possibly even think about developing another
institute at the National Institutes of Health to actually look at drug
discovery for some of these, what we would call orphan pathogens, and do the basic
work to come up with targets and particular lead molecules, and then turn it
over to industry to go off with the development.
That
is something I think we possibly should consider down the pike.
The
problem in industry right now is that anti-infectives are competing with CNS
drugs, cardiovascular drugs, and GI drugs that people have to take for the rest
of your life, so there are huge markets and huge sales, and the anti-infective
drugs are being prioritized down, and not going into development pipelines.
Most
companies need a potential market of $500 million to bring a drug forward into
development.
That
shifted the burden actually out to the biotech industry and there are a lot of
companies out there trying to develop antimicrobial agents, but I can tell you
the cost of developing is a problem in raising funds, and if you have been in
this particular area or even had any stock whatsoever, you will understand what
I am saying because at times, like three years ago, it was easy to raise funds. It is nearly impossible to raise funds this
year even to start-up companies with very good ideas, that two or three years
ago you could start.
So,
we are in what I would call almost a nuclear winter of funding for biotech
companies at this point in time, and you are going to see a number of those
companies go under.
So,
I think what is happening in the November workshop and with what Mark said will
happen in the future, I think is absolutely imperative, that is, regulatory
bodies, academia, and the pharmaceutical industry have got to get together to
streamline this process, so we can develop life-saving drugs coming now.
What
you need is microbiological superiority, you have to be active against the
resistant organisms, and you would like to have a drug that is not going to
develop resistance very fast. You would
also develop something that had a distinct pharmacological advantage, and
finally, something that had a safety advantage.
[Slide.]
We
have a well worked out paradigm. There
are some scientific holes in it, but we do have the paradigm that you work
first in the test tube to see if the bug is active, how it works, what its
mechanism of action is, is it a cidal drug, is there low induction resistance,
and is it active against both susceptible and resistant pathogens because you
can't determine a priori whether the patient has a resistant or a susceptible
pathogen.
The
next step is efficacy and appropriate animal models, and this is hotly debated,
with the key pathogens, both the resistant and susceptible pathogens, and also
bringing in the elements of pharmacodynamics in developing what levels of drugs
that you need. I know Bill Craig and
George Drusano have discussed that at many of these meetings.
The
pharmacokinetic requirements can be worked out ahead of time also. You need an I.V. drug for serious
infections. Many times you can switch
over to an oral drug if you have it once the infection comes under control.
We
need to know if the drug penetrates into the site of infection. John was talking about that strain in the
central nervous system. You need to be
able to penetrate into the central nervous system.
You
need to be able to penetrate into the alveolars to get aspiration pneumonia or
aerosol pneumonia. These are topics I think will be discussed this afternoon.
Finally,
there is the risk-benefit analysis with the safety database.
[Slide.]
I
borrowed a slide that Ed Cox showed at the meeting on the 19th of November on
how you get on the list, and I know this is going to be gone into in detail a
little later by John Powers, but I think there are two or three themes here, is
there sufficient prevalence, because if there isn't sufficient prevalence, you
are not going to be able to study it.
Two,
is the organism virulent, does it really have the public health importance that
we are talking about.
Then,
you go down to look at other sufficient therapeutic alternatives to really
justify going forward.
So,
what I would like to do for the rest of the talk, is kind of set some of the
themes on how you go forward.
[Slide.]
First,
the list. This is what David Ross
presented a couple of years ago in a briefing document. This list is notable in that some of the
newer resistant bugs, the Acinetobacters don't appear here, and I think this is
a class that probably should be added to these lists.
[Slide.]
We
do have very potent pathogens here. When
you look at the community-acquired, Jim just went over a number of them. We have some other areas outside the
gram-positives and the salmonellas and N. gonorrhea areas, so this is a list
that has to go forward.
We
have talked about the vancomycin-resistant Staph aureus and the looming problem
that may be coming.
[Slide.]
Jim
has gone into the multidrug resistance.
This is a study we actually had the Focus people do for us, to look at
the incidence of multidrug resistance in common and gram-positive pathogens,
and you can see it is significant when you sample 50 different centers around
the United States, so it is a major problem coming and it's a problem that is
changing over time, so a system has to be put in place to be able to track this
in order to identify the problem bugs.
We
see the case reports as we are hearing about some new resistances, but people
have to pay attention now to make sure they don't become a dominant pathogen.
[Slide.]
I
would like to use Staph aureus as a model on how you would get onto the list,
and you go back to some work, Chip Chambers published this actually in Emerging
Infectious Disease in 1999.
This
is what happened with penicillinase-producing Staph aureus. It appeared almost after penicillin appeared.
It became a real problem in the '50s in hospitals. When I was in training in the early '60s,
penicillin resistance was not a problem out in the community. Yes, you would see it occasionally, but you
can see very rapidly over the next two decades it became a major problem, and
now the penicillin resistance is out there.
[Slide.]
We
saw the emergence of MRSA. It was
low. Jim reviewed the history of
it. It is up to almost 50 percent now in
many hospitals, and this actually drove the use of vancomycin. You can see the tonnage of vancomycin used as
the incidence of methicillin-resistant Staph aureus came about. So, it does have an impact on the way the
physicians treat patients.
[Slide.]
In
the community now, are we seeing again what was seen with penicillin
resistance? We have high levels of
methicillin resistance in hospitals in nosocomial infections. We are starting to see it, and by word of
mouth, we are hearing from almost every city in the United States that a
significant percentage of patients coming into emergency rooms now have MRSA,
so I think this is one area that has to be monitored very closely, and it has
been seen in many different countries.
These
organisms are fully virulent, actually, they are probably a little virulent
than some of the hospital strains, and they have caused fatal infections in
children. It varies as high as 21 percent in Finland, and in some of the
localized communities, Indian American communities, there was actually an
incidence of 55 percent in the children.
As
Jim pointed out, these community-acquired strains are much different and they
are not the multidrug-resistant strains, but they have something else that is
much scarier. There was a recent study
presented at ICAAC with 32 community-acquired MRSA isolates, of those 32
isolates, 31 were producing the superantigens Enterotoxin B and C which causes
toxic shock.
So,
these are organisms that have high virulence factors that we may be seeing as a
major problem coming forward.
[Slide.]
Finally,
the VRSA that Jim has already talked about, the two strains, one from Detroit,
the other one from Hershey, Pennsylvania.
It turned out the Hershey patient also had a vancomycin-resistant
enterococci in the wound, but the strain was lost, so you really couldn't tell
whether or not that's where the vanA gene came in the Staph aureus in Hershey,
Pennsylvania, and the organisms are not related, which is another scary factor.
So,
I think this is what is starting to dictate is that we are going to need some
new classes of drugs to drive on for some of these resistances because, as Jim
pointed out, they are resistant to a lot of different compounds.
[Slide.]
We
just heard a little bit about the development of resistance, and this is a
slide Bob Moellering showed at a meeting I was at, and he looked at the rate of
resistance to vancomycin versus linezolid.
It took a long time for vanco resistance to come about.
That
is probably because it wasn't used much, because we had many other
anti-staphylococcal drug in the '70s and '80s, but when that tonnage went up to
treat MRSA, the bugs had to do something, and they did an architectural, an
engineering feat of putting eight genes together to overcome vancomycin
resistance, but once that genetic bridge was built, it can be traded around,
but it took 30 years for resistance to develop to vanco, but with linezolid, it
developed actually while the clinical studies were being done.
[Slide.]
There
was a paper in CID in January of this year of the compassionate use where they
had 19 cases emerge while on therapy, so it is a problem, and this comes back
to the question about the U.S., and those are point mutations giving the
resistance to linezolid in the ribosome, so they can emerge during therapy.
[Slide.]
But,
unfortunately, it has also emerged in Staph aureus, and I am aware of three
different isolates now of Staph aureus.
Well, what is the problem with the Staph aureus?
We
just heard maybe if you just drain it, it's okay, but if you look at
bacteremia, probably one of the worse infections you can get with Staph aureus,
and you look at the mortality, it is in the second set of bars, it's 30
percent. This is bugs that they kill
people in a high percentage.
Indeed,
the mortality rate with MRSA is even higher than with MSSA, but it is not only
true for Staph aureus, but coag-negative staph, enterococci, and Candida also
when it is in bacteremia, the mortality is high. This is studies coming out of Dick Wenzel's
group published in 1999. So, these are
organisms that cause a lot of mortality.
[Slide.]
What
about the pre-antibiotic era? This is a
paper by Skinner & Keefer back in 1941.
Staph aureus bacteremia had an 82 percent mortality. This is a real killer organism, and as the
patient population got older, as you can see on the graph, the mortality was
100 percent. So, with our aging
population and Staph aureus, this is a major problem.
[Slide.]
How
about if inadequate therapy is given?
Another slide that Dick Wenzel presented on data from Ibrahim in Chest
in 2000. If you look at patients with
intensive care unit bloodstream infections, and the numbers of patients are
fairly large here, if you get inadequate therapy, the mortality is great, it doubles
more than 50 percent.
If
you look at the patients, the organisms that were causing this mortality with
inappropriate therapy, it was two main pathogens, Staph aureus and Pseudomonas
aeruginosa. So, given the appropriate
therapy early on, it empirically, really changes the outcome overall.
So,
I think these are the type that have to be put together for different pathogens
to get them onto the list.
Dick
has also written a prospective article in JID in '99, looking at the impact of
therapy and attributed mortality, and as he says in that article, the
resistance genes just add to that mortality, so if you have a drug that treats
the resistant organisms, you can bring the mortality back down.
[Slide.]
Well,
what are some of the problems? We talked
about this a lot at the February meeting and at the meeting in November. I am just using some of my old slides there,
but one of the problems that we have right in the development of drugs is there
is very limited drugs in the pipeline.
The
promise that genomic sequencing in combinatory chemistry was going to cure it
has failed to date. We still think that
those new targets will yield some compounds in the future, but I think it is
going to be another 5 to 10 years before you start seeing those compounds come
down the pike, and we need substantial funding to continue that.
[Slide.]
I am
not going to go into the detailed drugs on the next two slides. You have those that you can look at. There
are two approved drugs here, and then there are five drugs being evaluated for
gram-positive infections listed. They are in different phases of development.
[Slide.]
Following
up on the ICAAC, and from data in the literature, there is another group of
drugs. These are all analogs of beta-lactams with activity against
Staphylococcus aureus. What it is, is
these compounds were engineered to bind to PBP-2a.
They
do it much better than most other cephalosporins and carbapenems, and there are
a number of them now going into development both in the United States and in
Japan. That is the cephalosporins. The carbapenems have not made it to
development yet, there is major problems in synthesis of those compounds and
whether or not they are going to be brought forward, and I included these just
for informational purposes.
What
is missing from the list? There is no
drugs for gram-negatives, and gram-negatives are a looming problem in the
hospital, and there is nothing that I see in the pipeline that is really going
to add to the armamentarium, and that's why we need to encourage the
development of drugs in this particular area.
[Slide.]
So,
what about development of drugs for resistant pathogens? You need to promote development and
appropriate use of them and the appropriate labeling. If you get restricted labeling, it is okay
for an MRSA, but for a more focused product like a VRE, it is going to really
negatively impact people developing drugs for that particular area.
But
basically, what you come down to is with enough safety database if there are
safety issues, but there is activity against resistant pathogens. That will actually control the use of drugs,
and I.V. drugs only are going to be controlled in hospital or in home I.V. use
anyway.
[Slide.]
I.V.
drugs are a problem to develop. You need
serious infections because patients have to be in the hospital. Selection of comparative agents, I don't
think is that much of a problem because there is a lot of drugs out there which
are considered the drugs of choice.
One
should select the best agent, though, and I think this is a part of the
monitoring by the FDA and Human Studies Committees to ensure that the best
therapy is given as a comparative agent.
I
think the criteria for oral switch are being developed with different partners.
[Slide.]
With
serious infections, there was a lot of talk about using surrogate markers with
clearing of the cerebral spinal fluid in meningitis, clearing the blood with
pathogens, but, of course, you need clinical outcome also, but the importance
of clearing pathogens out of the CSF has been brought up before.
Another
question on what is the number of pathogens that you need, and I think we are
going to be discussing that this afternoon, and the requirement for two
well-controlled studies, this is one of the major topics of this conference,
but there is another initiative that has been initiated at the FDA, which I
think industry should use more, and that is use the target package insert
initiative to really increase the communication and to clear up exactly what
has to be done, and increasing the use of that particular initiative may
actually help in the development of drugs.
[Slide.]
Finally,
how do we incentivize drug development?
This is really more a biotech field than a Big Pharma field. For
expanded access, there is the possibility of charging fees just to cover your
expenses or to augment what you are raising on the marketplace.
There
was a lot of talk about patent term extension at the November 19th meeting, and
this is the initiative talked about by Mark Goldberger, about extending and
giving a wildcard patent extension, that for developing drugs for niche
products, you would then put the patent extension onto another product, and
that drew a tremendous amount of enthusiasm from the Pharmaceutical
Manufacturers Association.
How
about funded consortiums? I think that
is a model, also cancer and AIDS has already had it, and we should move
forward.
One
of the other areas that was brought up by one of my colleagues at Cubist is
possibly the development of a loan system or government guaranteed loans. This would facilitate biotech companies being
able to access different types of funds than just the stock market, and being
able to develop funds.
There
are small business loans, but most biotech companies are too big to really get
into that particular area. That
particular thing could be modified also.
You
then repay the loans based upon once you have commercialized the product.
[Slide.]
The
final incentives are tax credits or deductions.
Right now it is only valuable for profitable companies, and there are
things to extend tax losses to carry them forward, so you do become profitable,
you can apply them.
But
the biggest thing, they actually have this in Canada and some countries in
Europe, you have a transferable tax loss.
A nonprofitable biotech company can transfer that to another company
that is profitable and some mechanism of raising funds.
These
are just some of the ideas that have to be developed in the future, and many of
these ideas cannot be worked on by this committee, but really have to be worked
on by Congress to pass some laws to get into this area for funding.
We
do have drugs coming down the pike to treat some of the pathogens. There are areas of problems particularly with
gram-negative where we need more research, and I think having the clear
guidelines of how to develop these drugs and then encouraging companies to get
into this area will help us in the future because of the emergence of these
resistant pathogens.
Thank
you.
DR.
LEGGETT: Thank you.
I
will open for questions at this point.
Don.
Questions from Committee
DR.
PORETZ: Frank, it is common for certain
organisms to use combinations of drugs, like Pseudomonas, people have been
using double agents for a long period of time, tuberculosis we always do, and
in the antiviral world with HIV disease we do.
Should
we be more commonly using combinations of drugs to hopefully prevent the
emergence of resistance for other organisms than the classic ones that we have
used?
DR.
TALLY: I think that is something that is
going to come, and you point to Pseudomonas for combination therapy, and
studies that were done a long time ago at UCLA for gram-negative bacteremia
combinations seem to work better also in the neutropenic patient.
So,
yes, it is a point in the future where combination drugs will probably be
employed. It is something that would
come in a Phase IV type of procedure, because in registering a drug, you need
to show that the drug, one, works, and, two, that it is safe in an adequate
number of patients, and it is very hard to do that when you are doing
combination studies initially.
So,
you need to do the first steps to show that you have a drug that is safe and
effective in treatment, and then for the resistant ones in the sicker patients,
in Phase IV, you could do the combination therapy, so I think you are going to
see a lot more of that.
DR.
LEGGETT: Alan.
DR.
CROSS: At our hospital, because of our
resistance problem, we have been, in fact, using more colistin than I have ever
seen used since I started training. In
our last talks, someone asked about the status or feasibility of detergent type
antibiotics, and I was just wondering given the resistance mechanisms we heard
about in the last talk, are there any resistance mechanisms we know about for
detergent drugs, number one, and, number two, these drugs have been developed a
long time ago and since then we have acquired increased skill in understanding
the structure-function relationships, and are there any efforts or do you think
there is any utility in perhaps going back to a drug like colistin, making some
modifications, and at least perhaps mining that area?
DR.
TALLY: That is an area that I actually
mined a while ago particularly to try and change the molecule, the colistin molecule
of polymyxa B, to take off the part of the molecule that was binding LPS to see
if I could use it in septic shock.
There
has been a lot of work on polymyxins and colistin to try and come up with
better molecules, and I haven't seen any data that they have been able to do
it.
The
inherent problem with those drugs, as you know, is the nephrotoxicity and that
they really stay in the vascular space and don't penetrate much. I think there are other efforts to look at
those molecules.
Now, the detergent-like drugs, you get to a point
where you can't give them because they are indiscriminate on all membranes, so
it is a fine line. I know there are two
or three efforts out there now that people are looking at those types of
molecules.
DR.
CROSS: Do we know anything about the
resistance mechanisms that may develop with those type drugs?
DR.
TALLY: No, not that I am aware of. Barth, do you know?
DR.
RELLER: No.
DR.
BELL: Frank, that was an excellent talk
as usual. You have to some extent
bridged the topics to be addressed in the morning session and the afternoon
session, and I wonder if you could help me right now, in response to my
question addressing the morning session, this concept of criteria for pathogens
or I might call it drug-resistant pathogens of public health importance.
What
is the relative importance of the two topics this morning and this afternoon to
the industry? In other words, I can well
understand the afternoon's importance because it impacts on the way you would
do studies and the materials you would have to submit for approval.
How
useful is it to you to have a list of criteria for drug-resistant pathogens of
public health importance stamped by some government agency, is that not
something you could figure out anyway or you and your investors could surmise
anyway, do you really need some sort of criteria like that or is it really only
as it might relate to this afternoon's discussion that that is of interest of
you?
DR.
TALLY: I think I hear what you are
saying, David. It is important for
us. One, it is important for the
discovery scientist to know what organisms we will be working on. That is at one level, that are going to
result in a compound that would have a commercial potential.
The
second part of the question is your ability to raise money. It is easier to raise money from very
skeptical investors, and they are all very skeptical, it is easier to convince
them if there is some type of broad criteria that you can then fit your
compound into or your organisms you are working into to increase the likelihood
that you can get funding. So, it is
important to the industry.
Now,
for Big Pharma, it is important for the discovery scientists in Big Pharma to
convince their upper management that they can develop a drug in this particular
area, so I think it is important in both areas.
DR.
LEGGETT: Frank, you made mention of you
first have to prove your drug alone works.
In that regard, could you mention some of the efflux pump attempts in
terms of looking at inhibitors?
DR.
TALLY: There has been a huge effort on
trying to develop pump inhibitors. It is
an area I personally have kept my research out of because when you look at the
genomes of many of the bugs, the versatility of their pumps is such that when
you turn one off, another one turns on, and so it has been very difficult.
You
can show for select strains that you can inhibit the pump and restore the
activity of ampicillin or one of the quinolones or fluconazole back to what it
was in fungi, but as soon as you start going out and do a survey, another pump
turns on at about 10-7, 10-8, and you are right back to
where you were with another pump pumping in molecule.
I
was into this area also when I worked at Lederle with the pumps for pumping
tetracycline. Again, there is a
tremendous genetic ability of the organisms to manipulate these pumps to handle
all the toxins because that is the way they make their living.
So,
there have been very good pump inhibitors, but none of them has reached the
stage of commercial development that I am aware of at this point.
DR.
LEGGETT: Thank you.
If
there is no further questions, we will take a break here and reconvene at
10:45.
[Break.]
DR.
LEGGETT: The next speaker will be John
Powers, who is going to talk to us about a list of pathogens of public health
importance.
List of Pathogens of Public Health Importance
John H. Powers, M.D.
DR.
POWERS: Thanks, Dr. Leggett.
This
is a continuation of our discussion that we started yesterday when we talked
about labeling for multidrug-resistant pathogens.
[Slide.]
What
I would like to show you today is some background on the requests that we have
had from folks in the industry to list resistant pathogens of public health
importance and why we even want to engage in this endeavor.
The second
thing I would like to go over is to elaborate on the criteria for listing
pathogens of public health importance, and you saw that on one of the Dr.
Tally's slides this morning, and then try to go into some information that we
at the agency have been trying to obtain on looking at those criteria and how
to obtain that data on looking at those things for each of the pathogens, and
then finally, some future plans for populating that list.
[Slide.]
As I
said, today is a continuation of previous discussions on development of drugs
for pathogens resistant to antimicrobials.
There were several Advisory Committee meetings on this topic in the late
1990s, but most recently, there was a meeting of this committee about a year
ago, in February of 2002, and then a workshop in November of last year
co-sponsored by the Infectious Disease Society of America, the pharmaceutical
industry, and the FDA.
It
is very clear from these meetings that one of the main topics is that
increasing in vitro resistance among many of these pathogens is becoming a
public health problem. In some cases already, this in vitro resistance is
translating into clinical failures, and even if we aren't seeing clinical
failure at this point, it may signal a decrease in the future usefulness of that
drug or drug class.
[Slide.]
In
November, at the workshop, there were discussions on the shifting of resources
within the pharmaceutical industry to the treatment of more chronic diseases,
something Dr. Tally already brought up again today, and there was a recent Wall
Street Journal article, and somebody sent this to me, and unfortunately, it
didn't have the date at the top of the clipping, so I can't tell you which
issue it was, but it listed the top 10 selling antimicrobials in the United
States.
I
just sort of condensed them all together and looked at the drug classes. There was not a single antimicrobial on that
list of top 10 selling drugs, and on those were antidepressants, anti-ulcer
medications, cholesterol-lowering drugs, and two drugs for anemia, but none of
them were antimicrobials.
So,
as Dr. Tally elucidated for us this morning, antimicrobials are not the
moneymakers for the pharmaceutical industry.
So, why even put together this kind of a list?
[Slide.]
Well,
at last year's meeting of this Advisory Committee, representatives of the
pharmaceutical industry requested that the FDA develop a list of pathogens for
which drug development was deemed of public health importance. Again, this same
issue was brought up in November of 2002 by both representatives of the
Infectious Disease Society of America and the pharmaceutical industry.
At
that point, we discussed, well, what would the criteria be for developing such
a list, and we felt it was important to come up with the criteria before we just
started putting names of pathogens on a long list, the reason being that
obviously, as Dr. Tally brought up this morning, this list would probably
change over time, therefore, it would be nice to have some uniform criteria,
and one of the other things Dr. Tally brought up is when a company wants to go
develop a drug, they want to be able to sort of plug this in for their
particular drug and the particular organism that they are looking at.
We
could take an example of this. For
instance, in the 1950s, in hospital-acquired infections,
penicillinase-producing Staphylococcus aureus was a scourge at that point.
One
could argue that there are plenty of drugs available now to treat just
penicillinase-producing Staphylococcus aureus, and one would not put just that
drug on a list at this time. However,
methicillin-resistant Staphylococcus aureus is a different story.
So,
you can see that some of these pathogens will change over time as to what would
be considered of public health importance.
[Slide.]
How would
we use such a list? Well, there is a
couple of points that are important to bring up, and that is to get on this
kind of a list, a pathogen would not need to fulfill every one of the criteria
to be on this list. We are just using
this as a kind of template.
The
other issues that we need to discuss would be the drug sponsors would still
need clinical data on treatment of resistant pathogens, as we discussed
yesterday in our discussion on multidrug-resistant Streptococcus pneumoniae,
and the reason we feel this is important is that there may be differences in
patient characteristics of those who harbor resistant organisms versus
susceptible organisms, and we feel it is still important to actually see
clinical information on the treatment of those patients.
One
of the other reasons that this may be important to have a list for the
pharmaceutical industry, that came up in November, was the idea that perhaps
these drugs could be given priority review.
Now,
it is almost impossible to designate priority review upfront in the development
process because as Dr. Goldberger brought up in November, whether a drug gets
priority review or not depends upon the results of the clinical trials, but at
least it would be designated that perhaps the drug might get designated as a
priority review.
For
instance, just recently--now, this is public knowledge--daptomycin has been
designated for priority review, as well.
Also,
drugs may still be approved, but not garner a resistance claim until there is
sufficient clinical data, and this is addressed as another important
point. The issue here is the drug will
be on the market and available for clinicians to use in their patients, but
until there is a sufficient clinical database, they don't necessarily need to
have a resistance claim.
The
example of this is levofloxacin, which was approved in late 1996, but didn't
garner a claim for penicillin-resistant Streptococcus pneumoniae until 1999,
when there was sufficient clinical data to support its efficacy in the
treatment of those organisms.
The
other important point here is that this is a list for prioritization, and Dr.
Leggett already pointed out in our discussions so far, we have essentially
talked about every bug you could possibly think of, but since this is for
prioritization, what we are trying to look at is what do we consider most
important.
So,
because an organism isn't on the list doesn't mean it is not important, but we
are trying to prioritize these things.
[Slide.]
So,
what we did, there were seven initial criteria that you saw on Dr. Tally's
list, and we condensed them down to six because it appeared to us that two of
them essentially were the same thing, and I will go through these.
The
first is that the organism is of sufficient prevalence in the population with
the disease under study, and I will talk about these in more detail through the
talk.
The
second is that the organism causes severe or serious disease. We changed this from virulence because we
didn't want to get into the issue of virulence factors as much as that those
virulence factors actually translate into high morbidity and mortality for
patients.
The
third is that the drug to which the organism is resistant is commonly used in
the disease under study.
The
fourth is that there is limited available therapies due to multidrug
resistance, and we had separated these out into two separate criteria before,
but then we figured, well, if it's multidrug resistant, that is why there is
limited available therapies, and we condensed that into one criteria.
Finally,
a drug is used to control spread of the disease in the population, and I will
give some examples of that, and then lastly, that there is a clinical
correlation of in vitro resistance with poor clinical outcomes.
[Slide.]
So,
let's go through each one of these, and I will try to show you some of the
information we have tried to put together for some organisms to put on this
list.
The
first is that the organism is of sufficient prevalence in the population with
the disease under study. The first point here is that this speaks to the
current burden of the public health problem.
If an organism is really, really uncommon, not to say that it is still
not important, but what is its relative importance compared to some to some of
the other organisms which may be more common for which we might desire drug
development.
Dr.
Tally also brought this up this morning.
If an organism is very, very uncommon, then, it is almost impossible to
get clinical information and to study it, as well.
As
we said, less prevalent organisms may still be important or they may become
more prevalent over time, and again this list should be a dynamic thing where
we will update this as time goes on.
Also,
this brings up an initial point here about linking the disease under study and
the organism, and most resistance labeling claims are related to efficacy in a
particular disease, so one could argue that perhaps an organism is important in
treating hospital-acquired pneumonia, but that same organism may not be as big
a deal when treating an uncomplicated urinary tract infection.
Also,
this provides the most helpful information to clinicians to show where the drug
actually works in which particular disease, and we will talk some more about
this issue of difficult diseases supporting each other this afternoon.
[Slide.]
So,
let's try to look at some information on how common are some of these
organisms. I am going to show this again
for some of the committee members that weren't here yesterday.
The
FDA has tried to obtain surveillance data in several ways, and one of the
things we have done is to obtain this information from Focus Technologies
through a contract that we issued last year.
We
got this contract for the purposes of identifying and tracking resistant
organisms of public health importance really for the purposes of drug
development. The Surveillance Network of
Focus Technologies includes 317 U.S. laboratories, and this information is
updated continuously. I will you some
information today as Dr. Jorgensen showed, something about penicillin-resistant
Strep pneumo and 14 percent of those organisms being multidrug resistant. That number is a lot higher now than when
that was published in 2000.
This
includes community, government, and university laboratories, and hospitals that
range from bed size of below 99 to over 500 beds.
[Slide.]
This
Surveillance Network also includes greater than 65 million antimicrobial
susceptibility testing results for various bug-drug combinations. It is not an active surveillance network, and
it is based on cultures which clinicians order.
We
looked at this in several ways. One way
we could look at this is per isolate, one way we could look at it is per
patient, and when we did it, essentially, the results come out the same. So, all the information that you will see
today is on a per patient basis, and we also looked at only one isolate per
patient.
When
we looked at that isolate, we looked at it from a first isolate per patient,
last isolate per patient, and it came out to be the same in most of the cases,
which brings up I guess an important point that Dr. Reller raised this morning,
about development of resistance on therapy, but for the vast majority of what
we looked at, the first isolate and the last isolate, the susceptibilities were
not different.
This
database includes over 500 microbial taxa and greater than 100 individual
drugs, and covers almost 3 million patients who are both inpatients and
outpatients, which gives us access to an estimated 2.6 percent of all isolates
tested per year in the United States, and some of the other surveillance data
is about less than 1 percent.
[Slide.]
Here
is some of the information that we tried to get to address this idea of how
common is an organism in the population.
As you can see, interestingly, of these greater than 500 taxa that are
in this database, only 27 of those taxa account for 95 percent of the
clinically encountered bacterial species.
So,
if you look at this, as Dr. Tally pointed out, Staph aureus seems to be a
fairly important organism here, 16.1 percent of Staph aureus make up this 95
percent, and the interesting thing is that the inpatient-outpatient split is
starting to get closer and closer, 9 percent of these are inpatients, 6.5 are
outpatients.
Although
we discussed Streptococcus pneumoniae at great length, you can see that
Streptococcus pneumoniae only account for 1.3 percent of this, with 0.7 percent
being inpatients and 0.6 percent outpatients.
There
is an obvious bias in this, and that is that the kinds of diseases in which
Streptococcus pneumoniae is most common, things like sinusitis, are also the
kinds of diseases where clinicians may not choose to culture patients, so again
there are some limitations in this data.
[Slide.]
I
apologize for this being very hard to read, but it is awful hard to squeeze 27
taxa onto one slide and to try to show you some of the quantitative
information, as well.
What
we have here are 27 taxa listed from most common to less common on this list,
and here is a point that Dr. Tally brought up this morning. If we look at the overall burden of disease,
the Enterobacteriaceae account for almost half of it, and yet we see very
little drug development for these gram-negative organisms.
When
we split them up by the top 10 Enterobacteriaceae, we have E. coli leading the
list, Klebsiella pneumoniae, Proteus
mirablis, Enterobacter cloacae, Serratia marcescens, Enterobacter aerogenes,
Citrobacter freundii, Klebsiella oxytoca, Citrobacter, Morganella on here.
Then,
we get down to some of the gram-positives with Staph aureus accounting for 16.4
percent, and as Dr. Tally pointed out in that Chest article, it was Staph
aureus and Pseudomonas that were the ones that had the excess mortality.
The
organisms that come up next are coagulase-negative Staphylococci, Pseudomonas
aeruginosa, and Enterococcus faecalis.
Enterococcus faecium again, although we have talked a lot about
vancomycin-resistant E. faecium, is 0.9 percent down here. Again, this isn't saying that these organisms
aren't important, we are just trying to put this on a relative scale compared
to some of the other things that we are seeing.
So,
the organisms for which we are seeing drug development, like Enterococcus
faecium and Staph aureus really the question is how do they fit in compared to
these gram-negatives where we are not seeing a whole lot of drug development.
Some
of the other things we see down here, Acinetobacter, stenotrophomonas, and then
we get to Streptococcus pneumoniae, viridan strep, group A and B streptococci,
Haemophilus influenzae, and anaerobes at the bottom.
[Slide.]
There
are some limitations to this data, as I said, as it is limited to what
clinicians actually order tests for. One
can make a case that penicillinase-producing and quinolone-resistant Neisseria
gonorrhea is an organism of public health importance, and yet when we went to
look for this, over this five-year span, we could only find 1,500 isolates of
Neisseria gonorrhea in this database.
Again,
I am not saying that this is unimportant, it just shows that unfortunately,
that we can't obtain much information and there are other mechanisms and I
believe the CDC has an active surveillance for looking for resistance in
Neisseria gonorrhea.
[Slide.]
So,
one of the other things that we can do with this database is to try to track
the proportions of infections over time to try to see which are increasing, as
well. So, what we have here is the
percent of all patients with bacteremias, and this goes from 1998 to 2002.
You
can see that there is a slight increase in all Staph aureus and plateaus out
from 1999 to 2002, but what you can see, at least from the data that we have
obtained, is that the number of methicillin-resistant Staph aureus bacteremias
is going up, and there has been a slight decline in methicillin-susceptible
Staph aureus bacteremias, so again this is just one way of trying to look at
the burden of disease.
[Slide.]
One
of the other things that bears discussing here is something that we talked
about yesterday, about trying to put into the label information on helping
clinicians to make treatment decisions.
One
of the things that still clinicians will need to look is what their individual
patterns of susceptibility are in their particular institution or their
particular community because when you look at the spread of
methicillin-resistant Staph aureus across 111 institutions in this database, it
is enormous, so if you practice over here on the far left, you have a less than
10 percent incidence of methicillin-resistant Staph aureus and perhaps you
don't need to worry about that when you are making treatment decisions.
If
you practice over here, you have got a big problem. You need to consider Staph aureus probably
every time you see a person who is infected with a gram-positive.
So,
looking at this information on drug-resistant pathogens isn't going to obviate
clinicians still needing to know what the resistance pattern is in their own
community.
[Slide.]
So,
let's move on to the second criteria. Do
the organisms cause serious and severe disease?
This is really information that we can just garner from the clinical
literature and what we know about the natural history of disease caused by
these pathogens.
Again,
resistance claims are usually linked to the disease under study. For instance, we have up to date granted
penicillin-resistant Streptococcus pneumoniae indications for
community-acquired pneumonia, but not acute bacterial sinusitis or acute
exacerbations of chronic bronchitis.
It
is also important about the range of organisms that cause various disease. If one were to grant an indication that said
for all resistant Streptococcus pneumoniae infections, that may not be very
informative to clinicians, and it also doesn't impact on things like Strep
pneumo causes respiratory tract infections, but it's an uncommon cause of
something like urinary tract infections.
Again,
these diseases range from fatal to self-resolving diseases, and it may be that
the impact of resistance is most likely to be important and relevant to public
health in the diseases which are not as likely to resolve spontaneously.
This
gets to an issue of making public health decisions versus decisions in
individual patients, so when we are approving a drug, we are looking at is this
drug going to be used in millions and millions of people to treat that
particular infection. That doesn't mean
we are telling a clinician that if they see a patient that has been treated
over and over again and has failed numerous antibiotics that they can't make a
treatment decision based on what they are seeing in front of them.
[Slide.]
So,
when we look at some of the stuff of splitting it up by source, this database
gives us the ability to actually try to look at where are these organisms most
commonly occurring. In this graph, what
you will see is splitting up the data on Staph aureus infections by source.
In
here, we will see the yellow bars are all Staph aureus, the pink bars are
methicillin-susceptible, and the orange bars are methicillin-resistant Staph
aureus. What you can see is that from
all sources, that we still see that MSSA outnumbers MRSA, but you can see that
there is big differences across these.
When
you look at bloodstream infections, they are pretty much getting equal to each
other. Upper respiratory tract infections,
it seems that methicillin-susceptible outnumbers methicillin-resistant, and in
UTI, actually, surprisingly, methicillin-resistant actually outnumbers
methicillin-susceptible although the overall numbers are quite small.
[Slide.]
So,
the third criteria is that the drug to which the organism is resistant is
commonly used in the disease under study, and this really speaks to the
clinical relevance of drug resistance.
Again, I gave this example yesterday.
One
could argue that trimethoprim sulfa resistance is a problem when one goes to
treat an uncomplicated urinary tract infection because that drug is very
commonly used. On the other hand, if
someone gave you the information that this young woman had an E. coli resistant
to Streptomycin, causing her UTI, that information is not very clinically
relevant since people don't use that drug to treat uncomplicated urinary tract
infections.
We
are attempting to gather information on drug usage for various diseases from a
number of sources, and actually it is quite difficult to split this up when you
try to look at what clinicians are using for a particular disease.
There
are a number of databases, like the IMS database, which look at overall drug
usage, but it is a lot more difficult when you want to piece it down to what
people are actually using it for. So, we
are trying to look at the IMS database, medical literature, and we are also
trying to contract with some other folks to actually obtain sources of
information from their practices about what folks are using for various
diseases, and this is because variations in medical practice and resistance
patterns in various geographic areas and patient populations may differ.
It
is interesting, when I was listening to the discussion yesterday, I think one
of the committee members said I don't think cefuroxime should even be on here,
it is not a problem, and the person sitting next to me said gee, that is the
drug of choice we use at our hospital for community-acquired pneumonia. So, I think there is differences across the
practices that may impact on this, as well.
[Slide.]
The
fourth issue is limited available therapies due to multidrug resistance. This is what we have tried to get a lot of
information on. So, we have tried to use
surveillance data to examine the relationships of cross resistance within a
given bacterial taxa.
I
showed you this data yesterday for Streptococcus pneumoniae, that the way we
are trying to look at this is if an organism is resistant to one drug class, is
it resistant to the other and vice versa, looking at it in both directions.
We
also plan to do similar analyses for other organisms, as well for fungi, and
what I am going to show you is some
preliminary analyses today that we have done for some of these organisms that
we are by no means complete yet.
We
assume that organisms which are resistant to multiple drugs are more likely to
have fewer available drugs for treatment, as well, which would seen to place
them higher on the list.
[Slide.]
So,
like I did yesterday, I want to show you a blank graph, so that we will have an
idea of what we are looking at. What we
have done is we have placed on the X axis the number of agents to which the
isolates are resistant.
On
the Y axis is the number of agents to which the isolates were susceptible, so
if you are right here, it means that these particular isolates that you will
see, and we put a number of dots across this here, each dot representing one
isolate usually, and so if an organism falls right here, it means that it is
resistant to nothing and susceptible to six different drugs.
If
an organism falls right here, it means it is resistant to one drug and
susceptible to five drugs, and then you will see these dots that kind of trail
off down here. What that means is that
an organism that falls right here is susceptible to four drugs, resistant to
one, and intermediate to one, just so you understand what you are looking at
when we do this, and then we will trail down here to the point when you get to
see these dots down here, these particular isolates are resistant to seven
different antimicrobials and susceptible to nothing.
So,
obviously, what we are really interested in is the organisms that are falling
down on this end. If we see
cross-resistance in these organisms, what we will then look for is clustering
of organisms here and clustering of organisms somewhere down here, as well.
[Slide.]
Let
me give you two examples of an organism that appears to be multidrug resistant
with linked cross-resistance pattern and one that does not.
Here,
we did the same analyses in almost 8,000 isolates of Acinetobacter
baumannii. The antimicrobials tested
across these seven things here are gentamicin, ceftazidime, imipenem,
ciprofloxacin, cefepime, ampicillin- sulbactam, and piperacillin. So, that is the seven isolates that run
across both of these isolates.
What
you can see is that the organisms either cluster right here where there are the
darkest dots, and that means that the organism is either susceptible to all
seven drugs and resistant to none, but right here is where we see the other
clustering of the organisms.
So,
if you have a resistant Acinetobacter, it is most likely to be resistant to
five or six other drugs and susceptible to only one or two at that particular
point. So, this way, we are looking at
it in both directions of not just starting out with, say, gentamicin resistance
and seeing how many are resistant to gentamicin, we are looking at it in two
directions.
[Slide.]
Let's
look at an organism that doesn't fit this pattern. This is Streptococcus pyogenes group A
beta-hemolytic streptococci. Here, we
looked at penicillin, vancomycin, erythromycin, clindamycin, ceftriaxone, and
levofloxacin.
What
you see here is that multidrug resistance is not a problem with group A strep. So, you will see that these organisms are,
for the most part, susceptible to all six of these antimicrobials, and there is
very few of them that are resistant.
Again, this trailing down here is a few of them will end up being
intermediate, as well, but when you look out here, there is almost none that
are multidrug resistant or very few when we get out to this point.
So,
if we are looking at this criteria at least of multidrug resistant,
Acinetobacter is clearly an issue here, but group A strep is not, and that
there are a number of other drugs that may be effective.
[Slide.]
Then,
we can actually take this information and do more detailed analysis on the
resistance patterns by taking these particular cells and actually looking at
the seven different drugs and trying to see whether they are resistant or not.
If
you just take this group right here where we are talking about organisms that
are resistant to six different drugs and only susceptible to one, that is
across this line here. The beauty of this
is you can actually look as we increase, you can see when you start to lose
particular drugs. I will show you this
for Streptococcus pneumoniae where it is a little easier because there are not
so many drugs across the bottom here.
But
what you can see is that once you get to this point with an Acinetobacter, that
you are talking about 98 percent resistance to aminoglycosides, 91 percent to
ceftazidime, 99 percent to quinolones, 97 percent to cefepime, 86 percent to
ampicillin-sulbactam, and 99 percent to piperacillin, and all you are left with
is imipenem, and even there, a third of the organisms are resistant.
So,
this is the kind of information we are trying to look at to say would an
organism go on such a list of public health importance because of the lack of
available therapies here.
If
you did the same thing with group A streptococci, you would see that 100
percent are still susceptible to penicillin, and a few of them are macrolide
resistant, but that most of them are still susceptible to all those other drug
classes.
Let's
do the same kind of analyses with Streptococcus pneumoniae, and I just want to
show you this to complete the thought that we did yesterday because I didn't
show you these when we were talking about multidrug resistance, but the
question came up yesterday of, well, most of these organisms probably aren't
resistant to two or three things.
Well,
at this point, it looks like they are, and you can see that if we split this
up, and we split this up just because if you overlay these two graphs on top of
each other, you can't see anything, so we split them up into
penicillin-susceptible isolates on the left and penicillin-resistant on the
right.
If
you susceptible to penicillin, most of these organisms still cluster right
here, meaning they are susceptible to erythromycin, third generation
cephalosporins, clindamycin, levofloxacin, and trimethoprim- sulfamethoxazole.
On
the other hand, if you start out with the penicillin-resistant isolate, you can
see most of these organisms cluster out here meaning they are resistant to at
least two other drugs in addition to penicillin, so it is not that if you are
resistant to penicillin, well, some of them are macrolide resistant and some of
them are just resistant to trimethoprim-sulfa, they are resistant to at least
three things.
[Slide.]
So,
again, we can do the same kind of information where we take this and look down
at this, and actually, we did it right here just to show the extreme case of
what's out here, but if we took this right here, you can do this for any of the
lines, so if you look at the two drug resistance line, you can see that 94
percent are resistant to erythromycin, 95 percent to trimethoprim-sulfa.
Again,
if you look down this list, you can see when you start to lose things, and you
can see that the first drug to go is trimethoprim-sulfa, the second class to go
looks like macrolides, and then the third class to go looks like clindamycin
here, but yet we maintain susceptibility of third generation cephalosporins
until we get way out here, and then you see that even there is 100 percent
resistance to this, as well.
The
reason I am showing you this is that what we would like to do is get your input
today on what kind of organisms we should run through this kind of analysis to try
to look at.
We
plan on doing this for the 27 different taxa that I showed you in the
beginning, but are there some other organisms that the committee would consider
important to try to do this analyses, as well.
[Slide.]
The
fifth criteria was that the drug is used to control the spread of the disease
in the population, and this is important for things like sexually transmitted
diseases like gonorrhea and tuberculosis where we don't have good vaccines
available, and really the means of limiting that spread of the organism in the
population is the drug therapy itself as opposed to, say, things like vaccines.
[Slide.]
The
last criteria is perhaps the trickiest one, and that is trying to draw a
clinical correlation between in vitro resistance with poor clinical outcomes,
and this really raises the question of is resistance in the test tube
clinically relevant.
The
reason why we also feel this is important is there are recent examples where in
vitro resistance does not correlate with poor outcomes in the majority of
cases, and there are other methodological issues when we expand this beyond
just bacteria, such as things with like tuberculosis where we know that
clinical outcomes don't correlate with some of the in vitro testing for some of
the anti-TB drugs.
But,
for instance, we know that some of the data we are seeing now on penicillin
resistance in Streptococcus pneumoniae at least in community-acquired pneumonia
shows that until we get up to MICs of at least four for Streptococcus
pneumoniae against penicillin, that there doesn't appear to be an impact.
Again,
this is the issue of the disease in question because for meningitis, there
appears to be that this may be more of an issue than for community-acquired
pneumonia.
On
the other hand, there is also some information in macrolide resistance in
Streptococcus pyogenes pharyngitis that perhaps that doesn't make a whole lot
of difference either.
So,
the clinical impact of resistance may be more important, as I said before, and
more apparent in more serious diseases which are less likely to resolve
spontaneously.
[Slide.]
It
is difficult to get information on clinical treatment outcomes. First of all, as Dr. Tally said, the organism
must be prevalent enough to even study and it takes time to accumulate that
data.
The
Pallares study that was published in the New England Journal of Medicine was 10
years' worth of data from Spain. Also,
some drugs are not used to treat a severe disease where the difference between
susceptible and resistant isolates are more likely to occur, and Dr. Tally
showed that slide about the attributable mortality between these things.
So,
for instance, in hospital-acquired pneumonia, it may be more apparent that
susceptible, and the data that Dr. Tally showed from the Ibrahim article in
Chest is about hospital-acquired pneumonia where you this big difference
between susceptible and resistant isolates.
On
the flip side of that, though, the cure rate for hospital-acquired pneumonia is
about 50 percent, so the overall cure rate is going to be lower although the
difference between susceptible and resistant isolates may be bigger.
On
the other hand, suppose you look at a study of community-acquired pneumonia in
PORT Class 1 patients, who are the least severely ill patients. The mortality in those people is about 0.1
percent. How are going to be able to
show a difference between susceptible and resistant isolates when a number of
the--now, obviously, that is treated patients, so we are not saying that
everybody would get better if they didn't get treated--but it is difficult to
show a difference in that.
We
can extend this to even other diseases like acute bacterial sinusitis where the
spontaneous cure rate is higher, it is a lot more difficult to show this.
The
other issue is where is your drug used, and we had this discussion back in
January about macrolide- resistant Streptococcus pneumoniae. Again, macrolides are usually used in these
people for things like community-acquired pneumonia in the outpatient setting
who are likely to do well anyway.
What
is the impact of macrolide resistance on that disease, it may be very difficult
to tell. The flip side of that is that
macrolides are very rarely used as sole therapy in the treatment of someone
with severe community-acquired pneumonia.
They are usually part of a combination regimen, so again it becomes very
difficult to determine what the impact of macrolide resistance is in that
organism.
[Slide.]
The
other issue is when we see increasing case reports, can we really call this mounting
clinical evidence, and there is a couple of issues that make that difficult to
evaluate.
The
first is that there is a publication bias, people are less like to publish the
fact that they put the person on a macrolide and they got better.
The
second thing is the natural history of the disease, such as community-acquired
pneumonia, where severe disease carries a mortality of approximately 30 percent
regardless of therapy. So, if you see
somebody who has severe community-acquired pneumonia and they were given a
macrolide and they didn't do well and they had a resistant organism, is it
because they had the resistant organism or is it because they were going to die
anyway from their underlying disease?
The
third thing is there are some data showing no effect of antimicrobial therapy
on mortality in the first five days of bacteremic pneumococcal pneumonia, and
this is data that Dr. Astrian did at Penn back in the 1960s, and there is no
reason to believe that that would be different. In fact, that is the reason why
the Feikin article in the American Journal of Public Health excluded patients
in the first four days of treatment because they wanted to take this into
account, as well.
The
problem with all these case reports is they lack comparative data showing a
higher rate of failure in resistant isolates versus susceptible isolates. So, for instance, when we looked at the data
for tolithromycin, we showed at that advisory committee that three of the five
patients who received clarithromycin, who had macrolide-resistant organisms,
one of whom was bacteremic, got better.
So,
when we look at this in a comparative way, the question is can we show that
these resistant isolates have a worse outcome, and this data, like I said, is
very hard to obtain.
[Slide.]
Some
people have done it, though, and I would like to show you some examples. This committee is pretty familiar with the
discussions about Streptococcus pneumoniae, so I wanted to use a different
example here of group A streptococcal pharyngitis.
This
was a study that was done in Italy in a four-month span in 1997. In Italy, their macrolide resistance is
actually quite high, it is almost about 50 percent of group A strep are
resistant to macrolides.
So,
they did throat swabs prior to treatment at the end of therapy in these
children all under the age of 14, and they looked at both the clinical
resolution and the bacteriologic eradication rate in these children.
Out
of those 3,000 kids who got cultured, 1,048 or about a third of them had a
positive test for group A beta-hemolytic streptococci. 934 of them were tested for susceptibility,
and all of those kids got looked at for clinical cure.
Only
668 out of the 934 came back for follow-up and that were able to be assessed
for bacteriologic cure by a second culture.
The macrolide resistance in their isolates at baseline was 46.3 percent
of the isolates, and one of the phenomenon I find very interesting is that
penicillin resistant was zero percent.
So,
I constantly ask myself this question - penicillin is used all the time for
various infections, why hasn't this bug become resistant to penicillin, and I
think that is a very interesting, if unanswered question.
[Slide.]
What
they showed was that the macrolide-susceptible organisms, which comprised 57 percent
of them, the bacteriologic cure rate which was done at the end of treatment, at
10 days, was about 80 percent of those people. Even though 42 percent of the
organisms were macrolide-resistant, almost 60 percent of them had a
bacteriologic cure anyway. So, there is
a big discrepancy, 20 percent more kids who had a resistant isolate still
eradicated the organism from their throat.
Now,
this goes to two different points here.
Is this because this is pharyngitis, which is a self-limited,
self-resolving disease in a lot of people anyway, or does it say that we are
defining these breakpoints in some wrong way and that the drug is still having
efficacy?
If
you look at the penicillin-susceptible isolates, 100 percent of these were
susceptible, and yet the penicillin only eradicated the organism in 84 percent
of the cases, so it shows that even in all susceptible isolates, that the drug
isn't completely effective all the time, and there is a whole body of
literature on this, too, that some people argue that perhaps other organisms in
the mouth secrete beta-lactamases which inactivate penicillin when you are
trying to treat group A strep, et cetera.
When
they looked at the clinical cure rates, it was low no matter which way you
sliced it, and, in fact, the failure rate with all these drugs was less than 2
percent at day 3 to 5 no matter which drugs you looked at, and they looked at
penicillins, cephalosporins, and macrolides in this disease.
[Slide.]
So,
what are some of the organisms that we have previously granted resistance
claims for that would seemingly be easy to put on this list? Well, we have talked at length today about
methicillin-resistant Staph aureus, vancomycin-resistant Enterococcus faecium.
In
the past, we have granted claims for penicillinase-producing staphylococci, but
one could argue that at this point in time, that doesn't really represent an
organism of public health importance, and it is probably subsumed under MRSA
anyway.
We
have granted indications in the past for beta-lactamase-producing Haemophilus
influenza and Maraxella, and most recently, for penicillin-resistant
Streptococcus pneumoniae, and we had the discussions yesterday of should we
now, knowing what we know, be calling this multidrug-resistant Streptococcus
pneumoniae.
Just
to reiterate some of the things we brought up
yesterday, some of the committee members talked about why don't we just
turn back the clock and remove this and just say community-acquired pneumonia
due to susceptible pathogens and forget about putting these resistance things
in there.
Two
of the points I brought up yesterday I think we need reiterating today. The one is not everybody who reads this label
is an infectious disease specialist, so we want to convey this information to
clinicians, and what do we want to convey, because somebody else said
yesterday, well, the label shouldn't be an educational tool.
It
says in the Code of Federal Regulations that the label is actually supposed to
show how the drug is supposed to be used for its intended use. The intended use is not for a bacteria, it is
for a disease, and those diseases for the most part are treated empirically
especially when we talk about Streptococcus pneumoniae, so what we are writing
this label for is not so just infectious disease physicians know how to use it,
but so how general practitioners and family practitioners and other people also
are aware of this cross resistance pattern between these organisms and what
they should be doing when they are going to treat people especially in an empiric
setting.
[Slide.]
So,
our future plans then will be to try to look at some of this information we
have gathered, examine the epidemiology of organisms and causing these various
diseases, obtain data on drug usage for some of these various indications to
see what folks are actually using for these, look at the cross-resistance
patterns in various organisms, and as I said, we would like some guidance from
the committee of--we will show that slide again of the 27 different taxa and
are there things you think should be excluded from that, that aren't important,
are there things you think should be added to that list.
Finally,
to try to obtain some data on clinical correlations with clinical outcomes and
resistance wherever possible.
[Slide.]
So,
what we would like to do is based on today's discussions, to at some point in
the future, and today we are not expecting to come up with a list coming out of
this meeting, what we are trying to do is to have the committee comment on
these six criteria for us that would make up such a list and see if there is
anything that we should add or subtract to that list, and then try to go back
and populate the list based on those criteria.
This
afternoon's discussions are actually going to talk about some other aspects of
drug development for resistant pathogens, which actually dovetail into this.
Then, we talked about yesterday this idea of multidrug-resistant organism
claims, which I hope we can expound on again today, and finally, all of this in
the end what we are trying to do is use it to formulate a guidance for drug
development for resistant pathogens.
DR.
LEGGETT: Thank you very much.
It
is now a little bit later, but we still have at least an hour or so of
discussion. So, go ahead. We have some questions first. Alan.
Questions from Committee
DR.
CROSS: John, that was a very elegant
presentation of the multi-resistance. I
wonder if you actually wrote down any of those organisms, for example, the
Acinetobacter, by site of isolation, and, if so, is there any difference in
terms of the likelihood of resistance at a specific site for a specific
organism.
DR.
POWERS: We are going to try to do
that. For some of the organisms, we are
going to try to split it up by inpatient and outpatient basis. We are going to try to actually look at it by
bed size of the hospitals. We are going
to try to look at it by geographic area, by census tract within the United
States to see if it varies across the country.
So,
we have got all of these planned analyses, and I was just trying to sort of
give you the tip of the iceberg today to see what it looks like.
DR.
CROSS: Certainly, in terms of the
organism by site, it may dictate the pharmacokinetics of the desirable drug
that you want.
DR.
POWERS: Right, and the other thing is
that when I put up some of those sites, like CNS, central nervous system
includes shunts, cerebral spinal fluid, so I just sort of gave you the broadest
brush approach today because some of those things may be more important than
others.
You
may complete ignore a coagulase-negative staph coming out of CSF, but not out
of a shunt.
DR.
LEGGETT: David.
DR.
BELL: The FDA, I believe is to be
commended for its continuing efforts to facilitate the process of new
antimicrobial drug development.
I
think I can understand the potential usefulness of developing a list of
criteria for drug-resistant pathogens of public health importance. I have some comments, that I am going to
defer until later, the most important of which is I think that the currently
proposed criteria need to be amended to include trend information.
I,
however, have serious reservations about the Federal Government actually
developing a specific list of pathogens stamped with FDA or Public Health
Service approval, and I wonder if it might be acceptable just to list criteria
that then could be evaluated as the drugs or brought forth.
Let
me outline my reservations about the specific list. One of them is that, of course, the list is
going to change over time or should change over time. Who would develop the list and how would it
be changed in a timely manner?
What
would be the impact on the industry and on efforts at new drug development if
the list changes over time particularly if a pathogen were to come off the list
because let's just say there were some wonderful new drugs developed or a new
vaccine that eliminated transmission to zero, or something like that?
Would
pathogens ever come off the list or would the list basically only grow and
become so long as to become meaningless?
My biggest
concern, however, is what about the pathogens not on the list? One issue is could work on these pathogens
not yield insights to help contribute to pathogens that are on the list. But my biggest concern about pathogens not on
the list is that the fact that they are not on the list might compromise
essential control measures to deal with drug resistance that, as we all know,
require approaches in addition to new drug development.
Let
me give you an example. Currently, the
FDA Center for Veterinary Medicine is engaged in a legal proceeding to try to
withdraw approval for fluoroquinolone use in poultry. We fortunately don't have much
fluoroquinolone-resistant salmonella in this country, unlike other parts of the
world, but we have considerable fluoroquinolone-resistant Campylobacter that is
linked to fluoroquinolone use in poultry, and it is the Campylobacter that is
serving as the basis for the FDA's legal proceeding to withdraw the
fluoroquinolones.
Now,
the FDA's legal proceeding is being fought tooth and nail by industry, tooth
and nail, and my question is suppose Campylobacter didn't turn up on this list
of priority pathogens for public health importance. I think it is virtually certain that the
industry would use that in contesting efforts to withdrawn fluoroquinolones
from poultry, and they would say, I think it likely, this is burdensome
regulation, see, it is not even an important pathogen, it is not even, et
cetera, et cetera, and I think has to be considered.
There
are other approaches to drug resistance in addition to new drug development,
and what would be the implications of a pathogen not being on the list?
So,
I wonder, in closing, if it's possible to develop criteria, perhaps even with
some examples, but stopping short of actually enshrining some sort of specific
list.
Thanks.
DR.
LEGGETT: Ellen.
DR.
WALD: Just to make two comments. One is that although antimicrobials may not
be on the list of drugs that you generated for overall, certainly as you look
at hospital formularies, they are usually right there on top. Now, I suspect that the hospital-based
dollars is relatively small compared to all dollars, but nonetheless, I think
important.
Secondly,
I would just like us to not exaggerate the nonsignificance of drug resistance because
I think that in reality, it is probably almost all significant and that the
fact that some infections do okay on drugs to which they are reported to be
resistant, really reflects the relevance of the breakpoints for the particular
sites of infection, and that, you know, when you get to central nervous system
disease or you get to an empyema or you get to middle ear disease where you
have a significant stepdown of antibiotic concentration from blood to site of
infection, then, in fact, you see very clearly that these drug-resistant
organisms are important and pathogenic.
DR.
LEGGETT: Barth.
DR.
RELLER: I like the criteria that John
condensed for the developing list and I wonder a couple of things, whether the
caveats that Dr. Bell has articulated could not be encompassed by a wording
"including but not limited to" on this list, and with specific
examples.
One
could argue, for example, for Campylobacter, that it is important to clearly
certain antimicrobials curtail resistance, issues of day care, public health
interest in containing infection.
But
in addition, I wonder, John, on the scattergrams that you did, and given the
utility of the TSN database as being one of the better, perhaps the best
currently available, that monitors, is a good sampling because of the diversity
of hospitals involved, so that one doesn't get biases of the high concentration
of resistant organisms in tertiary care hospital, but doesn't ignore their
importance because of the past trends of what appears first in these centers
eventually wends its way to communities.
It is just a matter of how quickly.
And
the complexity of dissecting out all of those shadows and dots is to develop
subset data, and I am thinking about Item No. 2 on the list, organisms that
cause serious and severe disease, of using the bacteremia isolates in that
database as a first cut for rank ordering of pathogens with multidrug
resistance.
The
utility of that I think is more than what is immediately obvious. In complicated urinary tract infections, resistance
may not be important or uncomplicated or not as important, but if one has
bacteremia, I mean by definition, one has upper tract disease and a complicated
infection.
So,
you pick up those pathogens that in different sites may be important, and you also
deal with the issue of an organism means different things in different places.
Similarly, most coagulase-negative staphylococci that are isolated and in the
database, many are rubbish, whereas, the ones out of blood, particularly if one
follows the newer guidelines in hospital-acquired infections,
catheter-associated infections where there is a reproducible isolate of
coagulase-negative, given how frequent they are, even though 80 percent may be
contaminants, the 20 percent that aren't can cause serious disease including
the occasional community-acquired endocarditis with coagulase-negative
staphylococci, so that you have a natural selecter, if you will, that everyone
would accept as serious and severe disease.
There
is also some additional regulatory support for that approach in that some of
the surrogates, with the emergence of resistance, for example, in VRE, one of
the things that was important in the consideration when
quinupristin-dalfopristin came before the committee was the use of cessation of
bacteremia, and I think of Dr. Jorgensen's portrayal of the persistence of
bacteremia from the Acar publication with third generation cephalosporins and
methicillin-resistant staphylococci of the early data of where despite aberrant
or inappropriate testing, that now doesn't happen in any good laboratory, one
could have been misled by in vitro susceptibility, but clinical failure.
So,
I think mining the data that gives a cross-section of the country would be
perhaps much more valuable than all of those numbers and all of those points
that may obscure the central issue of these or by definition important
organisms associated with serious disease.
You
can actually cover, not only one, but some components of more than one of the
six points in doing that.
DR. LEGGETT: John, what do we do about the not prevalent
pathogens that we can't study that are of immense public health interest? For instance, anthrax, or viruses.
DR.
POWERS: Some of the things we have done
with anthrax, there has also been a recent animal rule where we are trying to
get information in things that cannot be studied at all, to try to get that
information.
The
original anthrax approval was based on a study done in Rhesus monkeys, that
looked at the efficacy of ciprofloxacin, doxycycline, or penicillin versus
placebo.
DR.
LEGGETT: Yes, Mark.
DR.
GOLDBERGER: I think that brings up, you
know, sort of the broader issue, which is related to some of the things we are
going to also talk about this afternoon, but in terms of thinking about how to
study organisms that are hard to study.
An
example that came to mind, I was just looking, you know, at the Acinetobacter
data, to actually do a study to really determine if a new antimicrobial worked
against the Acinetobacter would be a major undertaking.
So,
the question comes up how does one go about making inferences, what are the
other components of information you can use to get a feeling of whether a new
antimicrobial is going to perform.
As a
starting point, obviously, that includes looking at in vitro data, perhaps
commonality of resistance mechanisms, the use of animal data, the study of the
drug in perhaps serious indications analogous to where you would find the
pathogen you are concerned about with other serious gram-negative organisms including
those that have similar resistance mechanisms, but it may be worth, at some
point, whether we do it now or in part in the afternoon or at a subsequent
meeting, talking about this concept of how one draws inferences from a variety
of types of data to allow one to be reasonably comfortable that even if the
number of actual isolates is not that high of the organism in question, the
totality of the data that you have collected makes it reasonable to presume
that this drug is likely to perform.
I
think that that is an important issue because even beyond the Acinetobacter, I
mean we have had concerns about resistant gram-negatives in a variety of
settings, to ask companies to come up with enough of each of the types of
gram-negatives to get that clearly put in the label is no small undertaking,
and the question is at what point, when you have looked at serious infections
due to a couple of, say, major gram-negatives, say, a klebsiella, an
anaerobacter, a pseudomonas, and you have shown the drug performs well, do you
begin to get enough confidence to be able to say you will label this for, say,
this type of a disease, due to gram-negative organisms more broadly.
But
I think at some point we are going to need to have a type of discussion about
how one draws inferences because there will be many examples of these
hard-to-study, very resistant organisms that we need to collect useful
information in some organized fashion about.
DR.
LEGGETT: John, one follow-up question,
can I play devil's advocate for a second.
Since we first saw penicillin resistance and sulfa resistance, hasn't
all drug discovery been driven by resistance?
In other words, criteria No. 4, isn't that self-evident?
That
sort of gets a little bit back to David's question, but in a different way.
DR.
POWERS: My answer would be sort of in
that we are actually in the process now of working--one of the things that came
out of that November workshop was this idea that some of this has to be changes
in the law.
The
IDSA is actually trying to go to Congress to actually lobby to do some of these
changes, and we are working in cooperation with them to try to look at what are
companies actually submitting to us, not by drug name, but just sort of broad
categories.
What
we are seeing, and this has not been completed yet, though, is that the number
of new molecular entities is actually quite small, yet, the number of changes
in formulations, such as extended releases or increasing the dosage of a
particular drug, is what we are seeing a lot of.
So,
when you say isn't all drug development driven by resistance, partly, yet, it
is changing your dosage formulation from the tid drug to a q.day drug, is that
driven by resistance or something else?
DR.
LEGGETT: Money.
Alan.
DR.
CROSS: I was just going to re-emphasize
Dr. Goldberger's point that we are not simply talking about organisms like
Acinetobacter that are hard to study.
Over the last 15 years, we have been involved in the preparation of
hyperimmune globulins and vaccines for things like Pseudomonas and Klebsiella,
which were high on John's list, and it is a major undertaking to find enough
centers that have enough of this disease to actually do a study.
So,
it is not just the Acinetobacters and stenotrophomonas, that is of concern, and
perhaps looking at common resistance mechanisms and being able to perhaps pool
that data may be of some use.
DR.
LEGGETT: Celia.
DR.
MAXWELL: Yes. As I was looking at the six criteria for
developing the list, I was a little bit concerned that I didn't know where I
would fit an organism like falciparum malaria.
That is not prevalent in this country, but certainly it is deadly, it is
prevalent worldwide in areas of the world, and we have an increasing risk of,
let's say, sending troops or something like that, that are going to have an
immediate exposure.
Where
would we fit something like that?
DR.
POWERS: I don't think we put the moniker
in this country on the end of prevalent, so certainly you could argue that
might be the prevalence of the disease in study. Falciparum malaria within the disease malaria
is very common and very prevalent. I
don't think in any way we meant to say just in the United States.
DR.
LEGGETT: Jan.
DR.
PATTERSON: I think the idea of a list is
helpful. I think that would be helpful to
industry to have some specifics, and it could be reviewed periodically to keep
it up to date.
I
have a little bit of reservation about prioritizing just the bloodstream
isolates because, for instance, a lot of the catheter-related infections,
taking the catheter out is the major therapeutic maneuver particularly for
things like coag-negative staph, and for an infection, say, like Pseudomonas
pneumonia, I mean a lot of times that is a lot more severe infection, but you
don't have a bacteremia from it.
One
way we have kind of gotten around, you know, giving us an out for just certain
organisms on a list per se, for instance, at our hospitals, for the use of
contact precautions, we say it's for multidrug-resistant and epidemiologically
significant organisms, so that kind of gives us an out.
Like,
for instance, Clostridium difficile, which we don't really think of as
multidrug resistant, it epidemiologically significant and has some of the same
implications, and maybe some of the bioterrorism organisms could fit in the
same way.
I
don't know if Salmonella and Campylobacter were on your list, but I think that
probably fluoroquinolone resistant, foodborne pathogens like that should be
included.
DR.
LEGGETT: Did you want to say something,
John?
DR.
POWERS: I just wanted to answer Jan's
question. That's the kind of thing we
are actually looking for, because when you realize most people don't culture
when they have foodborne disease, so that is not going to show up on our list,
but clearly you can make a case that that should be on there, as well.
There
is a list of bioterrorism things, and sort of get this idea of making a list
and the Federal Government making a list, the Federal Government has made a
list. This is a list for
bioterrorism-related agents. So, it is
not as if we are doing something that is completely out of the realm of
possibility here.
DR.
LEGGETT: Mike.
DR.
PROSCHAN: I am taking a risk here
because I am just a country statistician.
I am from Heart, Lung, and Blood, but I am trying to understand why the
drug resistance doesn't correspond to poor outcomes necessarily. Actually, I don't even know the exact
definition of drug resistance, but I am assuming that that is entirely in
vitro. Is that right, the definition?
DR.
LEGGETT: Yes.
DR.
PROSCHAN: So, is it possible that the
body, you know, is able to handle a certain amount of infection, so that even
if the drug kills half the bacteria instead of all of it, now your own body is
able to fight the rest. Is that a
possible?
DR.
LEGGETT: That has been the major problem
of trying to compare antibiotics to other drugs, because there is three parts
of the equation instead of just two, so, it is not drug and us, it's drug, us,
and bug.
David.
DR.
BELL: I had a few comments on Table 1,
the criteria that I just wanted to mention.
The title, I would suggest that the title encompass the concept of drug
resistance as opposed to just saying criteria for pathogens of public health
importance, because, you know, there is influenza and there is anthrax, there
is all kinds of things, and this is really about drug resistance, something in
the title to that effect.
Point
No. 1, I wonder if it should be "or" in the disease under study
rather than "and."
Point
No. 4, a few alternatives to treat the pathogen, I wonder if there should be
some concept of ease of treatment, oral therapy, empiric therapy--
DR.
LEGGETT: Dave, could I interrupt a
second?
DR.
BELL: Yes.
DR.
LEGGETT: Are there any more questions
for John's talk before we jump over, because, John, were you going to lead the
discussion? No? Okay.
So, we can jump on over. Finish
what you were going to say, and then we have this page here of Points of
Discussion.
DR.
BELL: Okay.
DR.
LEGGETT: It's not that I want to shut
you up.
DR.
BELL: The agenda kind of looked like it
all went together, and I apologize, I didn't see that.
DR.
LEGGETT: I know. That's a trouble we are all having.
DR.
BELL: Do you want me to just--
DR.
LEGGETT: Go ahead, jump in.
DR.
BELL: Well, I will just finish. I mean ease of treatment, oral, empiric. No. 5, there is no vaccine for that
pathogen. I would suggest delete that
parenthetical phrase because even when there is a vaccine, there is still going
to be people getting sick and they are going to need to be treated, and the
vaccine won't be offered for everybody or efficacious for everybody.
But
the most important thing, something about trend information. We have run into this situation a lot where
criteria for regulatory action, preventive action, whatever, tend to focus on
rates rather than the trend.
Thanks. Sorry.
DR.
LEGGETT: No, no, if you look at the
bottom the page, that is exactly where we want to start, so that was fine. I just thought John was going to lead.
DR.
POWERS: The slide I showed about the
Staph aureus bacteremias that we were intending to look at trend information
over time, as well, but we could certainly add that in, be a part of criteria
No. 1.
DR.
LEGGETT: Go ahead, Jim.
DR.
JORGENSEN: I would like to suggest adding
to these criteria. So far, we have
talked about resistant organisms and the need for new agents, but I am also
concerned about infections in which very effective agents may no longer be
available or may cease to be available.
Specifically,
I am thinking about gonorrhea in which the four recommended agents currently,
two fluoroquinolones in which resistance is common in some parts of the world
and becoming more so in this country, and where the only other oral agent is no
longer going to be available, so it may leave only one injectable drug that is
predictably active against gonorrhea.
DR.
LEGGETT: You mean by the pharmaceutical
agents.
DR.
JORGENSEN: Yes.
DR.
LEGGETT: John.
DR.
BRADLEY: Just a concept that
unfortunately adds to the problem, not solving it, and it's in response in part
to Dr. Frank Tally's presentation earlier this morning.
It
takes several years once you identify a problem to actually bring a drug to the
clinicians, so that they can use it. So,
in putting together these criteria, and I think you have done a really nice
job, I suggest that we cast a wide net because you don't know which of these
resistances 10 years down the road is going to be giving us lots of problems,
and if you restrict your criteria, then, someone will say 10 years from now,
gee, you were shortsighted and only look at the most prevalent likely
pathogens.
As
our ability to determine molecular mechanisms of resistance improves, it
complicates things further. When I was
in my fellowship, there is resistant Pseudomonas to ceftazidime and now it can
be beta-lactamase, PORN [ph] deficiency, efflux pumps, and God knows what else
is going to come up, and now we know these mex pumps can pump out not only
beta-lactams but fluoroquinolones and probably a lot of other agents.
So,
it becomes more difficult predicting which of these mechanisms of resistance is
actually going to be a problem, and the time to development of agents is huge.
Secondly,
and in addressing one of the points for discussion regarding not having enough
patients with a particular organism, I think with the animal models that have
been developed, that you were involved with, with Dr. Craig, with neutropenic
mouse, Rhesus monkey models where you can actually model drug exposure for a
pathogen in a particular issue and get an idea of the Cmax to MIC or AUC to MIC
that is required in the animal model.
I
believe a lot of that information can be extracted into the clinical situation,
so you don't need nearly as many patients to prove that a drug at a certain
dose will work if you have laid all your groundwork with the animal model and
then just a very few patients to confirm that the animal model is predictive
will net you more information on fewer patients for these very resistant
organisms which may be very rare.
DR.
LEGGETT: John.
DR.
POWERS: Could I ask you a question about
animal models because, Jim, you asked this now, and, John, you brought it up a
second time.
I
want to refer to something we saw yesterday.
One of the thing Mark was talking about was sort of building this body
of information to show that the drug may be effective for a resistant organism.
What
we saw yesterday was a drug which claimed to be effective for
quinolone-resistant organism, and Pete Dionne, our microbiologist, showed an
animal study where even though the dose was doubled, that it still did not
eradicate the organism from the mouse's lungs.
I
was interested to hear, then, as we went around and talked, several of the
committee members said, well, this is a drug effective against
quinolone-resistant organisms, so it gets to be the point of how does one
interpret that animal data when you see it and extrapolate that to what might
happen in people.
DR.
LEGGETT: That is the point of contention
that one of the speakers at the open session is probably going to address.
Mimi.
DR.
GLODE: I have two comments. I just wanted to reinforce what Dr. Reller
brought up and then comment on Dr. Patterson's comment on that. I do believe that some patients--and also
referring to Dr. George McCracken at an earlier meeting--some patients are more
informative than others, so bacteremic isolates, CNS isolates, and therapy for
those patients is more informative to me than many sputum cultures with the
resistant organism.
But
then I certainly took your point that perhaps more in adults than pediatric
patients, catheters are removed when there is a catheter-associated
bacteremia. In most of our oncology
patients, the first issue, if one is not desperately ill, is to treat through.
So,
the catheters are left in place, repeat cultures are obtained, and antibiotics
are provided, and this is a real challenge at the neutropenic host, et cetera,
but that would be the standard in our hospital for pediatric oncology patients,
so one has the opportunity then to say can this drug eradicate this organism in
this setting, which is a significant challenge.
One could then argue that that is a pretty informative situation.
My
second comment goes back to the Wall Street Journal and anti-ulcer medications,
but I just have to say this. I haven't
read the labeling for any of these anti-ulcer medications, but with regard to
physician education and perhaps patient education if you can get your hands on
the PDR, I mean I hope they all say that the patient should be evaluated for
the infectious organism that causes ulcers and then treat it appropriately with
the antibiotics to eradicate it and be cured.
DR.
LEGGETT: They are all getting them
anyway for their viral upper respiratory tract infections.
Jan.
DR.
PATTERSON: Well, I just wanted to
clarify. I was thinking more about
short-term catheters and ICU patients.
We also treat through in adults for the long-term catheters.
DR.
LEGGETT: Barth.
DR.
RELLER: Fusing the amplification of this
information about the catheters, to me, a critical issue here is separating out
the ones that, by definitions that have come up at the FDA having to do with
what documentation would be required for studies and indication for
catheter-associated bacteremia, because if one had an agent that actually was
effective in clearing the bacteremia with the catheter in place by whatever
mechanism, the new agent, given the frequency and the increasing importance of
this organism and the increasing importance of these catheters as lifelines for
the kinds of patients that are growing exponentially in healthcare in this
country, and with home I.V. therapy, et cetera, a really rigorous definition of
catheter-associated bacteremia and something that would work with or without,
and clearly the discussions of guidelines for that include whether or not the
catheter is removed would be very helpful.
I
didn't mean in any way to imply that only bacteremia would be a way to get at
this, but rather that it would be perhaps the most efficient first cut at what
everyone would accept as important, plus recognition that in, for example, CNS
infections, a very high proportion of those patients, if they were done, would
have concurrent bacteremia, perhaps a higher association than with any other
entity apart from infective endocarditis in terms of the proportion who would
have a positive blood culture to deal with, Listeria or, in the old days,
Haemophilus influenza type B or the pneumococcus.
DR.
LEGGETT: What I would like to do is talk
a little bit more these criteria until people have discussed it under 10
minutes, and then go on for 10 minutes and talk about sort of the second point
about the 27 taxa and the other sort of analyses before 12:30.
Before
we go off the criteria portion of this, I would like to ask, where do you fit
in, say, in drug development, something that alters things, so, for instance,
we know P-glycoprotein, that we never even thought much about in terms of HIV
is now probably more important than what we used to think of as the cytochrome
p450 in terms of making drugs ineffective.
Where
do you tie in, and then sort of the whole efflux pumps in bugs are sort of
equivalent to the MDR in cancer sort of chemotherapy, and I am sure, I can
envisage a new drug development not at a particular pathogen, but at something
that would enable the drug to work much better in the body.
Where
is that subsumed in this or is that just sort of in a parallel universe in
terms of deciding that something is important, because theoretically, I could
think of a process by which a drug that inhibits P-glycoprotein would be of
immense importance for a bunch of drugs.
DR.
POWERS: I think what you are getting at
is the bigger issue that we always talk about, and that is what we are really
trying to treat here is a disease. It
just so happens that in anti-infectives, that that disease is associated with
an infecting pathogen.
Since
a lot of these diseases are treated empirically, we usually ask that that drug
show efficacy against the most common organisms that are likely to be
encountered.
So,
for instance, if you were developing a drug for meningitis and it had
absolutely no activity against the pneumococcus, but was a great Neisseria
drug, what do you do with that, because, you know, the people are going to
apply it empirically.
I
guess if somebody came in with a drug like that, that had some kind of effects,
it would depend how the drug works, but I would assume it would have to have
some effect on the bacteria, or if it doesn't, they would have to show that
leaving the bacteria alone still somehow cures the disease.
DR.
LEGGETT: Ellen.
DR.
WALD: I just wanted to make one comment
about group A strep and which I think is an organism in which looking at
antibiotic resistance is particularly difficult especially, currently, you
know, in part, because it is definitely a self-limited disease, so from the
clinical perspective, you might never notice that there was antibiotic
resistance, we are in an era now where almost no one is collecting isolates
certainly from patients with pharyngitis because they are doing so many rapid
diagnostic tests.
Again,
even the availability of organisms and testing them, you know, has
diminished. So, I think that we might
not notice that as a problem unless there was an increase either in invasive
disease or acute rheumatic fever, so that might be something that we need to
keep our eye on even though it might be harder to do and harder to interpret
what's happening clinically.
DR.
POWERS: I think what that gets at,
though, what I was trying to draw there in that, was the link between
resistance and a self-limiting disease, and how it is to show that resistance
has an impact.
Again,
getting back to this issue we talked about yesterday of the drug label actually
trying to convey some important information to clinicians, I guess you could
sort of use the other upper respiratory tract issues that we have, are the
diseases like acute bacterial sinusitis and acute exacerbations of chronic
bronchitis where we are dealing with again a self-resolving disease, and yet
drug sponsors have asked us several times for resistance labeling claims for
those diseases, but pharyngitis is the example of where there is data available
to show that, gee, perhaps the resistance doesn't impact on that disease.
That
is not to say that for something like community-acquired pneumonia that it
would.
DR.
LEGGETT: Ken.
DR.
BROWN: I have no idea what the topic
under discussion is right now, so I thought I would raise a couple of points of
my own.
I
would like to focus on something Frank Tally said because I think it goes far
beyond the scope of most of our comments, and that is, that several things
which have occurred and the state of things as they are, there is little to no
hope that the drug companies are going to be able to develop adequate answers
to these problems.
I
think if you look at the fact that most of the available antibiotics, and I
think all of the antituberculous drugs were discovered by or before 1975, and
since that time we have had almost no new classes of compounds discovered.
That
is frightening if you knew the numbers, and I wish we would give them to the
statisticians, the numbers of soil samples that have been screened in the last
45 or 50 years by the pharmaceutical companies.
I
think it is fair to say that there is essentially no chance that the
pharmaceutical industry by itself can come up with the answer to this
problem. I wish I could say Frank were
the first person to suggest this kind of a consortium, but actually, the president
of the IDSA, in 1978 or so, in his closing remarks, suggested that the very
formation of such an institute which would be responsible for the discovery and
development of new anti-infectives.
I
think all this is complicated by something you just mentioned, Jim, which a lot
of us haven't come to fully appreciate, and that is the role of P-glycoprotein,
and some of us don't even know what it is, and MDR, and the interesting problem
that some of us want the protection of P-glycoprotein to keep drugs like
ivermectin out of the CNS, and others of us who treat cancer want to get rid of
P-glycoprotein, so we can get the drugs into the CNS.
When
you then combine that with the multiple drug that the patients who are being
treated for HIV and have an effect or are affected by p450 or have an effect on
P-glycoprotein, this geometric increase in the need for knowledge is
horrendous, and I think that to say that we are going to have a productive
result from this small part of the discussion is a little bit scary, especially
when, as Mark points out, we can't expect to really get even a list today and
the slow rate at which we function as organizations contributes to this, and I
don't know that there is an adequate way to get around the speed of our ability
to do things, but I don't think it is going to be within the purview of the
industry to do this, period.
DR.
LEGGETT: Barth. Didn't you have your hand raised? You are too depressed after that.
[Laughter.]
DR.
RELLER: I was trying to digest it. Just a follow-up to Dr. Wald's comment, and I
realize why virulence was taken out of this and embodied in the serious, and
how one could minimize the importance possibly in those places where it is a
self-limited disease, but if one had to pick among the common bacteria, one
that intrinsically is virulent, I would choose a group A streptococcus because
of how quickly and how devastating it can be in certain clinical pictures.
If
we were to have resistance in group A streptococcus, we would have a real
pathogen on our hands, and I think that one should be on the list because of
what Dr. Bradley mentioned earlier of this timeline of how long it takes. I think it is second to none in its intrinsic
virulence.
DR.
LEGGETT: I would like to expound a
little on that if I can, bringing it back to the point of trying to get back to
the Campylobacter issue and my sort of pet peeve is Neisseria gonorrhea.
I
think if you are dealing with a pathogen that only has a human reservoir, that
has immense potential pathogens we want to be preventive and that might have to
be either another criteria or folded into the ones that are in that list, to
talk about what if type things.
We
have sort of done it with Staph aureus because we now we are all nervous about
being in the pre-antibiotic era again, but what happens, the same thing could
be applied to group A strep or to the Neisseria or bring those things into this
discussion.
Alan.
DR.
CROSS: I wanted to ask the FDA or
perhaps John, what types of contacts do you have with other organizations, not
just here, but around the world, the globalization issue. Part of that is we have talked about not
having enough glue-based strep, but in the military, they have really some
serious outbreaks every few years even recently.
I
don't know if there is any sharing of those isolates with the nonmilitary
organizations. Similarly, we heard about
the resistant pneumococci in Hong Kong.
Is there any type of surveillance program for bacteria that we have for
influenza in terms of sampling around the world and trying to find out what's
on the horizon, perhaps getting access to those organisms?
Then,
there is the other issue in terms of trends, what David talked about, is that
MRSA actually started in Europe and was there for a number of years before it
occurred here. It was rather benign
there when it first started, and then once we had MRSA here, it was a more
significant clinical problem.
My
understanding is it is less of a problem in Europe now. So, the point is that there are some global
trends associated with these organisms that may be instructive in terms of how
we deal with things.
Is
there any actual sharing of either data or specimens, for example, comparing
your data under contract with perhaps what is going on elsewhere?
DR.
POWERS: We are also part of an
interagency task force on drug resistance that had a meeting prior to ICAAC
last October or September, and where this issue was discussed--David, you set
that up--about trying to get--and there is a whole section on surveillance, in fact,
David is probably better equipped to answer this than me because he was the
chair of that section.
But
we are trying to get that kind of information. Focus Technologies tells me that
we have the ability to get some information from outside the United States, as
well, although we haven't tapped into that as yet to try to see, but that is
one thing we could do would be to try to compare.
DR.
LEGGETT: To follow up on Alan's
question, is this sort of a project that is also undergoing discussion in Europe
and abroad, sort of like along with the harmonization sort of globalization and
that sort of thing, or is this just solely a U.S. initiative?
DR.
POWERS: David Bell is probably better to
answer this because we were talking about all of this stuff.
DR.
BELL: Is what in particular under
discussion?
DR.
LEGGETT: This project to try to come up
with a list, in other words, the fact the United States prioritizes it or
somehow allows industry to do what they want.
DR.
BELL: You know, this is a particularly
opportune discussion because I am actually about to go for a three-month detail
to WHO to help them identify ways to implement their global strategic plan on
containment of antimicrobial resistance.
Of
course, surveillance is a major issue.
There are a lot of major obstacles to good surveillance. We have had discussions both a CDC and I know
elsewhere, for example, the EU, their surveillance system.
They
phrase it in terms of marker pathogens, and we have looked at this concept also
to try and get away from this idea that some are more important than others for
the reasons I mentioned, but just marker pathogens, and it would be Staph
aureus and pneumococci.
The
EU has a very nice sentinel surveillance system in their countries, and they
have I guess it's pneumococci, VRE, I believe it's Staph aureus, and I think
they just added E. coli, something like that.
Again,
they are not trying to say these are the targets for drug development, they are
trying to harmonize surveillance efforts in different countries in their
jurisdiction and use these as, quote "important," unquote, marker
pathogens, and I suspect we will see more of that around the world, but this is
actually a very interesting discussion to me because WHO is kind of looking for
what to do next.
DR.
LEGGETT: Ken, it sounds as it you are
pretty pessimistic even if there was this production of a list and there were
incentives, as Frank talked about, in terms of providing money or those sort of
things, you are basically saying even if there were much more incentives to
come up with drugs with new mechanisms rather than me-too's or extensions of
patents by, you know, increasing the milligram dosage, you are pretty
pessimistic that that is even possible, is that the gist of what you were
saying?
DR.
BROWN: If you try to count the number of
rational drugs which have been put together, trimethoprim sulfa, that makes
one. That was really based on
permesamine [ph] and sulfa, which preceded it.
That is actually the only one I can think of--
DR.
CROSS: Influenza drugs.
DR.
BROWN: And then if I look at the number
of isolates which people look at, it is not that people have stopped looking at
isolates, but 25 years ago, in a screen of 3,000 soil samples a month, 99.9
percent of the compounds which were isolated were already known.
So,
what I am saying is the discovery of perhaps ivermectin from a soil sample next
to a sludge sewer in a Japanese golf course grew Streptomyces, but we haven't
had a lot of additional new compounds since that class.
So, all
I am saying is statistically, we need to do several things better, and I don't
think that just depending on companies that have to try to make money to keep
themselves in business is going to be an adequate situation knowing what we
know and the increasing demands of the scientific community, which are
appropriate, and the additional information.
When
I think about the use of the macrocyclic lactones in combination of HIV drugs
in Africa, where the CYP450 is not the same for people who live in Ethiopia and
the southern tip of the Arabian peninsula versus the rest of the world.
It
seems to me the complexity is frightening, and we need an institution bigger
than any pharmaceutical group that I know of to participate and probably to
lead it.
DR.
LEGGETT: John.
DR.
BRADLEY: I think the pessimism about
industry not developing new drugs is certainly in part based on the fact that
the financial incentives, the disincentives to develop a drug and lose money
are huge, and there are both pharmaceutical company funded and NIH funded
studies in looking at mechanism of resistance, so on the one hand, we are
moving forward quickly in developing information on why the drugs are
resistant, but the other side of the coin, moving forward quickly in developing
drugs to meet the resistance has been the problem.
I
think there are several ways that were brought up in November, brought up again
today on how to get rid of the financial disincentive. I am sure that PhRMA has incredible resources
to be able to approach these problems if given the right incentives, so I don't
share the pessimism of Dr. Brown that it can't be done, I just think that the
equation of how progress is put together needs to change.
In
addition, there as we get more involved in mechanisms of resistance, perhaps on
this list somewhere, knowing that many of these mechanisms of resistance cross
between organisms by cassettes or plasmids, that as a mechanism of resistance
of public importance goes on this particular list, like efflux pumps, that that
can be a target for facilitating pharmaceutical industry development of drugs,
as well.
DR.
LEGGETT: Barth.
DR.
RELLER: Dr. Brown, the pessimism, I
wonder, as a provocative question, the problem that the home runs of the past,
what is found in sewage, that the problem is a repetition of a failed or
nonproductive model as opposed to an entirely different approach, in other
words, the success of the past may be an inhibitor for the future.
In
other areas, non-antimicrobials, I mean the advances have come by an
understanding of receptors and blockers, et cetera, so that maybe the approach
is not looking in sewage or natural compounds, but rather an investment, and it
may require, as Dr. Tally pointed out, a leap forward in terms of an institute
that looks at basic science, that these cassettes, for examples, that Dr.
Jorgensen, to actually understand the components, what turns them on and off,
et cetera, and that the model for new drugs would be at that level as opposed
to finding the needle in the immense haystack that has been part of the past
discovery approach.
What
do you think?
DR.
LEGGETT: And then can we then come from
a firmament and then go right to the very concrete before we go to lunch.
DR.
BROWN: I think it is important for me to
reflect that I didn't believe that diesels would replace steam engines with
which I grew up. I was working in
Ethiopia at the time of the smallpox eradication program, and I didn't think it
would work.
So,
while I had great hopes for the new information we have about genetics, I have
to look realistically and say we thought we would have great advances in sickle
cell disease from what we have known about the genetics of that disease or
those 29 changes, and not a whole lot has come out of that, so I don't have as
great hope for the wonders that we were going to get from the knowledge of the
human genome yet, and it may take a while and I may be hopefully shown to be
very wrong.
The
final example I would give, we were told maybe seven or eight years ago, boy,
once we get combinatorial chemistry going, it is just going to revolutionize
things and we will have so many new things that you don't know what to do with
them.
Of
course, there is always a bottleneck after that, so I hope that I am wrong,
however, I would love to see better ideas, and I think Frank's is a great one,
that we need to pull together and get our heads together, and I agree with
Barth that we should probably stop looking at just sewage sludge.
DR.
LEGGETT: David.
DR.
BELL: I have one other question. It might still be in the firmament, but
recently, there have become enormous amounts of new resources available for
issues related to the bioterrorism agents, diagnosis, treatment, and so on, I
mean really enormous, and I am wondering if somebody from the pharmaceutical
industry might comment on how they see, if they do, attention to the
bioterrorism agents, which are microorganisms, after all, how some of that
research might be leveraged into antimicrobial drugs for more common pathogens,
I think the mechanisms have to be, you know, if we are talking basic research
in drug development.
DR.
LEGGETT: Do you want to say something,
Frank?
DR.
TALLY: There are a couple of
points. It is in the firmament, this
could go on for four or five hours talking about it. What we have to do is think out of the
box. What Ken is saying is the old
methods have wringed all the water out, and that is you still wring the thing,
you are just not going to get any more, so you have to think of a new way to do
it, and I think that is what we have to do with the genetic information we
have, and the next round is the financing, and it is look not just for drugs,
but for vaccines for stimulating the immune system, and that type of thought
has to start going in.
For
the bioterrorism, people are working on that area, and there is now being
grants coming into companies to try and look at new targets, and you can use
anthrax as one of the ways to do that, a lot of common genes between anthrax
and other gram-positives, the same as with gram-negatives.
DR.
LEGGETT: What I took away from your talk
was one of the basic things is that the science of antimicrobial drug discovery
has to go back in a sense and be validated by the NIH, which kept telling us
for years, oh, there is already a way to do that, we are not going to fund it,
so in terms of getting back to the government and pharmaceutical agencies.
DR.
PORETZ: Could I just ask one quick
question about the surveillance network?
Your contract to Focus Technologies, what was it, 317 labs, are those
all in-hospital labs?
DR.
POWERS: They are in-hospital labs, but
they are hospital labs that also function as central labs for communities, as
well.
DR.
PORETZ: So, you get outpatient cultures
in addition?
DR.
POWERS: Yes.
DR.
PORETZ: And you have been doing that for
a period of time? Is that recent or
what?
DR.
POWERS: Is our contract recent or has
Focus been doing this for a while?
DR.
PORETZ: I mean that information, who is
getting the information, is it just going to the FDA or is it being
disseminated to anyone else?
DR.
POWERS: Well, if you want to go pay
Focus to get it, I guess you can get it for anyone else.
DR.
PORETZ: No, but you get it.
DR.
POWERS: Yes, the information that we get
from them, we contracted from them to obtain.
DR.
PORETZ: And what do you do with that
information, just keep it internally?
DR.
POWERS: One of the things we are doing
here is trying to use it to make this list.
The other thing is once we get your input, we actually plan on publishing
some of this information in cooperation with them, as well.
DR.
GOLDBERGER: But it is important, just to
mention, this is a contract that became effective only this past October, so
some of the data you have seen is data we have only just started to get within
the last month or two.
DR.
LEGGETT: Speaking to that point, has
anybody been able to come up with other bugs they would like to have the sort
of analyses we were shown done with in, for instance, group A strep was
mentioned, and I see that is on the list of beta-hemolytic strep.
DR.
POWERS: I heard Salmonella and
Campylobacter as two other organisms.
DR.
LEGGETT: Salmonella and Campylobacter,
which I did not see there.
DR.
POWERS: No, they are not on there. Neisseria gonorrhea is not on there, which
was one of the questions, I wanted to see if people thought that that was
important to put on there.
DR.
LEGGETT: Go ahead, John.
DR.
BRADLEY: That's a pretty long list. Did you want to prioritize them the way the
government did with bioterrorism agents, like A, B, C?
DR.
POWERS: If you would like to. I mean one of things I didn't want to come
across is saying I didn't think group A strep was important, that wasn't what I
was trying to say. One of the points I
tried to make about the list is what do we see in the pipeline for development
for E. coli, which is way at the top of the list? Almost nothing.
So,
I guess the idea would be prioritization.
I look at group A strep and I think, gee, that's a really severe
disease, but then I look at the cross-resistance pattern and I see six other
drugs to which that organism is susceptible including penicillin and
clindamycin, which are the recommended drugs for severe group A strep
necrotizing fasciitis. So, not to
minimize its importance, but how does that compare to a Pseudomonas that's
resistant to seven drugs, and I guess, John, that's your question about
prioritization.
DR.
LEGGETT: The logical first step in going
through that is to take your criteria number--whichever one is that there is
few options available and go that way, so you work your way back from zero
drugs to one drug, to two drugs.
DR.
POWERS: I guess one of the things we
might address then, rather than putting the bugs in first, is go back to the
criteria and say which of those criteria should we rank in such a way as to be
more important.
DR.
LEGGETT: Go ahead.
DR.
GESSER: Richard Gesser from Merck
Research.
I
would like to suggest along the lines that John is thinking, ESBL, Klebsiella,
E. Coli, to start the conversation perhaps.
DR.
LEGGETT: Good.
Anybody
have any other suggestions? Go ahead.
DR.
PORETZ: I couldn't see that list very
well. We Mycobacteria and tuberculosis on that list?
DR.
LEGGETT: No, I think this is just
typical bacteria.
DR.
POWERS: That is actually a good
point. This is all typical
bacteria. We didn't try to branch out
yet into those other things. Like I
said, we are going to probably do this kind of analysis for fungi and other
things, but this was our first pass. As
Mark said, we just got a lot of this information.
DR.
LEGGETT: Go ahead, Jan.
DR.
PATTERSON: I guess with regard to
prioritizing the criteria, I might see No. 4 as one of the higher priority
criteria, limited available therapies due to multidrug resistance, and that is
kind of what has driven a lot of our concerns in recent years.
DR.
LEGGETT: I think in terms of
prioritizing the list, where you could get your most bang for your buck is
similar to the ESBL thing, where you could take care of both klebs and E. coli
sort of at the same time, you know, sort of a common resistance mechanism, and
then go from there.
I
think, in general, another of the reasons to have this is I think it is going
to give us lots of information about the cross-reaction of resistance mechanisms
that we don't appreciate. We may think
we know them in the abstract, but we don't really see how interwoven they are.
Go
ahead, John.
DR.
BRADLEY: I think the fact that Jan
pointed out that multidrug resistance is a priority amplifies the fact that if
it's multidrug resistant, there are likely multiple mechanisms of drug
resistance including PORN changes, ESBLs, other beta-lactamases, efflux pumps,
the whole nine yards.
DR.
LEGGETT: Alan.
DR.
CROSS: Just to re-emphasize the point
that is made, we have had a whole series of, quote "new" antibiotics
based on combining inhibitors of a resistance mechanism with existing drug, so
perhaps something aimed at at least a few identified mechanisms mixed with the
existing good agents we have, would also start a new class of drugs.
DR.
BRADLEY: How do you exactly want us to
do this right now?
DR.
LEGGETT: I don't know. The first I saw what we were supposed to be
doing--
DR.
BRADLEY: Is someone supposed to be
putting a list up here?
DR.
LEGGETT: I don't know that this morning
we want to come up necessarily with the dominant list unless you guys tell us,
I mean I didn't think that was the purpose.
DR.
POWERS: I think the things we would like
to know are - we have six criteria up there, Dave Bell, you commented on some
of the things we should add into this or subtract out, and that is the kind of
comments we were looking for, are there some changes that we should make to
this criteria, and then one of the clear things I am hearing is No. 4 should be
No. 1.
Is
there any other way that we should prioritize
those? What I thought I heard was
it sounds like No. 2 ought to stay No. 2 from what I heard from Drs. Wald and
Reller about group A strep. Any other
ranking of those things, should we change that?
DR.
LEGGETT: No. 1 should be No. 6.
DR.
PATTERSON: I would probably put the
clinical correlation, I would probably put that higher up, like 3 or 4.
DR.
BRADLEY: I think we should assume for
purposes of the discussion that if it's resistant in vitro, that you will have
a poor clinical outcome. In terms of
linking the two, I think that's a completely different discussion how closely
they are linked, but I think as we prioritize, to make it simpler, if it's in
vitro resistance, in making the list, we should assume that you can't treat
them with standard doses of drugs in the clinical arena, and then this
afternoon talk about that other issue perhaps.
I
would take it off the list.
DR.
LEGGETT: I think I sort of would, too,
because whether it's not the case now, it may be. I am not sure how that really helps us cull
out things that we are not going to look for even though you have got some of
the examples.
DR.
POWERS: Maybe I should clarify a little
bit, and this has to do with the discussion we had yesterday. When we come down to it, what end up doing
with this is putting a bug-drug combination in the label, and that ends up
being for a specific disease.
The
reason why No. 6 is really there is this idea about suppose somebody comes in
with a new drug, say, for instance, for macrolide-resistant group A strep, and
they say, look, we are great for pharyngitis, does that really help the public
health?
So,
I guess what is missing from this list or I didn't make clear enough was the
idea that this resistance claim that we are going to the label is an organism
linked to a specific disease, much like we were talking about yesterday,
multidrug-resistant Streptococcus pneumoniae for community-acquired pneumonia.
So,
that is why No. 6 is there, to try to lean it towards the diseases where
resistance is more likely to be apparent instead of telling a drug company to
spend all their money studying pharyngitis.
DR.
LEGGETT: Okay. Barth.
DR.
RELLER: I would be interested in Dr.
Jorgensen's comments on Item No. 6, but thinking about that, one could consider
6 an NCCLS issue and indeed the committee is constantly trying to make sure
that the detection of resistance is clinically important.
I
think as an excellent example, Dr. Bell's comment earlier about resistance to
fluoroquinolones among Salmonella is not that big of an issue here in the
United States. Actually, I wonder about
that, by what criteria. Most of the resistance, if not all of the resistance to
fluoroquinolones, which is a major problem in typhoid fever, at least as drugs
are currently used in some parts of the world, and as reviewed by Dr. Perry in
his New England Journal review a couple of weeks ago, and under discussion and
a working group in NCCLS is that the organisms look susceptible, but relative
to yesterday's discussion, when there is a single mutation, they are nalidixic
acid resistant, and the discussion of whether the criteria are appropriate or
even the breakpoint criteria for Enterobacteriaceae with ESBLs, if we had the
breakpoint criteria that the Europeans have, whether or not they are ESBLs in
the phenotypic strict sense, organisms would look resistant based on dropping
the MICs that constitute susceptibility.
The
prevalence of single mutations in typhae strains in the United States, many of
which are acquired abroad, about 80 percent, but also in foodborne salmonella,
the single mutations that are nalidixic acid resistant as presented at the IDSA
this autumn, are actually substantial.
What
does that mean clinically? Well, perhaps
the most important thing it means is that you have got one hit, and when you
get that second hit, they are probably not going to work, and it's easier to
get maybe the second hit if you have already got the first hit.
So,
I think it is an event waiting to happen, and that may be where you can get the
mileage on this whole business about the quinolones in poultry and the feeds is
that first hit although it is silent by NCCLS criteria currently, and maybe
silent clinically with appropriate duration and dosage of fluoroquinolone in
the therapy of typhoid fever.
It
is a failure waiting to occur with an additional hit. So, I think the main importance of No. 6 in
my mind is reinforcing the importance of keeping the clinical laboratory on
which all surveillance is based, be it bioterrorism or hospital infection
control practices, or therapy of the individual patients, or the database on
which the targets for future drug development are prioritized, to keep the
scientific integrity including being linked, not only with phenotypic
characterization, but as Dr. Jorgensen so eloquently presented, keeping that
matched with the basic science underlying the mechanism of resistance is a
fusion that is critical to maintain and to recognize that in some infections
with some organisms, you can get clinical success because of the nature of the
disease itself despite resistant other organisms, but in some infections like
meningitis, you get autolysis-deficient pneumococcus.
We
want to make sure that the in vitro recognition of that keeps in sync with the
clinical reality of it. So, I think
actually this is a very important issue to keep the clinical and laboratory
things, getting the same answer, so to speak.
Jim,
what do you think?
DR.
JORGENSEN: Well, I think while it is
very complicated to do so, it is important or we are finding it more important
to index the interpretive breakpoints with the site of infection or the type of
infection.
Clearly,
that is the case with penicillin and the cephalosporins with pneumococcus. But I think there are other resistance
mechanisms that we have debated. For
example, it has been debated whether macrolide efflux-resistant Strep pneumos
are really significant in community-acquired pneumonia.
The
argument has been made that those drugs achieve very high levels in the
epithelial lining fluid. The MICs for
those strains are not unreasonably high, they are maybe in the range of 4 to
32.
So,
the argument has been made that this is an in vitro phenomenon, it is not
significant. I would cite to the
contrary, the four patients that were reported from the University of North
Carolina, who were treated as outpatients for community-acquired pneumonia with
oral macrolides and who came back to the hospital bacteremic and had failed
that therapy, and all four of those had efflux-resistant strains.
Moreover,
the CDC has had an ongoing study of persistent positive blood cultures in
patients who have bacteremic pneumococcal pneumonia, and if you look at the
agents they are treated with, most of them are macrolides, most of them have
efflux mechanism.
So,
I think one thing that is clear is not everybody that has a strain we would
define as resistant is going to die or is even going to fail in a dramatic
sense, but there will be a percentage of patients who do not do well, and I
think that percentage is worth paying attention to.
DR.
LEGGETT: Alan.
DR.
CROSS: I think in Item 6, it is
important, but there has to be a huge caveat there, and I would like to talk on
behalf of the host. The point has been
made about informative patients, and I think that is really critical, and I
would like to just remind everyone that we were unable to show that
antibiotics, that appropriate antibiotics were effective in gram-negative
bacteremia, which ought to be fairly straightforward, until the McCabe-Jackson
criteria tossed out the uninformative patients who were destined to die anyway.
So,
what happens is how we define the informative patient in Item 6 is really
critical. It has to be done in a very
careful way if Item 6 will have any futility at all.
DR.
LEGGETT: Do you think focusing a study
on neutropenic sepsis, getting back to the positive blood cultures, that is the
only two things you have got, is the bug and the drug.
DR.
CROSS: Well, I mean when Dr. McCracken
was here last time talking about meningitis, I think that also is an idea
situation. We have the experience which
we discussed yesterday of levofloxacin in bacteremia with penicillin-resistant
Strep pneumo. We had 15 cases of that.
So, those were highly informative, good patients, and it does not have to be a
huge study, but it is a lot easier to evaluate.
This
becomes particularly relevant for the ESBLs because the patients that tend to
have serious infections with those organisms are very complicated patients,
many of whom, even under the best of antimicrobial care, will not have a good
clinical outcome, and those have to be really separated out carefully.
DR.
LEGGETT: We can continue to talk over
lunch, but those comments take us perfectly into the discussion we are going to
have this afternoon about one study versus the other and the quality of the
data.
Since
we are running a little behind time, why don't we just break for lunch, and we
are scheduled to be back here at 1:30 for the open public hearing. At 2 o'clock, John Bradley is going to talk
to us about how clinicians use data for clinical decisionmaking.
[Whereupon,
at 12:45 p.m., the proceedings were recessed, to be resumed at 1:30 p.m.]
A F T E
R N O O N P R O C E E D I N G S
[1:40
p.m.]
Open Public Hearing
DR.
LEGGETT: The first speaker is Jerry
Schentag. I hope you can introduce yourself and give us your two cents worth.
DR.
SCHENTAG: I will introduce myself. There may be someone in this committee I
haven't spoke in front of yet.
Jerry
Schentag from the University of Buffalo.
I have working relationships with most of the pharmaceutical companies
in the area of PK/PD and I will declare that upfront. If I missed anybody, you know where to find
me.
But
I think I would like to just make one or two small points, some of which is to
answer things that are already talked about this morning and a couple of
questions that have been asked that I think I have some information to help
with.
Then,
in another more central point, which perhaps I will state first, and that is,
that with AUIC or any other index of pharmacokinetics and pharmacodynamics, we
have had a pretty good run here working with clinical correlations and also
explaining I think one of the most important things which we have talked about
today, which is bacterial killing rate and also bacterial resistance.
The
point I want to make about that is that it is the same number that describes
the threshold of killing and the prediction pretty reliably of resistance. So, whatever you think of the absolute value,
whether you agree with me that it should be pretty much 100 for everything or
whether you think it should be different by different drug class doesn't matter
in this statement.
The
point is, it is always a predictor of resistance if you set your drug dose
against an MIC of an organism right where you see the threshold at the
beginning of your good effect.
Now,
why is that important? Well, it answers
the most fundamental question of all, which is that PK/PD actually predicts the
effect of the drug on the organism. It
may not have much to do in some clinical scenarios with what happens to the
patient, but it has a lot to do with the organism, so that is the territory
that we wish to stay in, and your pathogen list can actually be resorted
against the drug classes and predict which ones are going to develop resistance
based on their current therapies, because this is selection pressure you are
talking about.
So,
for instance, John earlier asked why group A strep is not a problem for
pharyngitis while the macrolides do have a problem. It is very simple. You are always over 1,000 for your AUIC even
with the lowest dose of Pen-V K against strep group A.
With
the macrolides, you are never much above 20 or 30, numbers which we normally
associate with resistance or at least a prediction of it fairly soon. Vancomycin, which Frank talked about, he
talked about it in the context of why it took so long it develop resistance.
Well,
there are actually two scenarios of vancomycin resistance that are worth
talking about. One is, of course, VREF,
which happened first, and then MRSA.
Well, with staphylococcus, vanco always had values of 4- to 500 because the
MICs were down around 0.5 or lower, and the blood levels were always high enough
on the AUC side, so that 0.5 into 250 or so would give you 400 to 500.
Now,
why did E. faecium go first? Very
simple. Sensitive E. faecium run around with MICs of 4. Well, if you divide that into 250, that is
approximately 62, it drops below 100, and quite a few years ago already, we did
a small analysis of our patient population and sure enough, all the E. faeciums
that start out 4 and sensitive were selected to develop resistance by
vancomycin treatment.
Then,
if you do that in a hospital population
with just about any drug, you should see the same thing, so it's
predictable.
This
is perhaps a bit more pertinent, and this is my last point today, because
yesterday, we went after the question of the quinolones finally targeting Strep
pneumo with a high number. That's the
first time we have actually formally targeted a PK/PD value around 250 or
higher for the pneumococcus.
Up
until now, we have been working on a situation where the dosing gives us 40
most of the time against Streptococcus pneumonia, so I mean we will see whether
that is soon enough to help, but my view is, is that all of this is
predictable, and the pathogen list ought to be set with some thought in mind
for the drug and the dose and how that interacts with the MIC of the organism
population.
So,
you sort your organism population in such a say that you see the easy-to-kill
bacteria where you are over 1,000 like the quinolones against Haemophilus, for
instance, and the hard-to-kill ones, like Streptococcus pneumonia and
pseudomonas, and then is you set your dose in the range where you are always
low or just at the threshold for animal models that suggest bacteria static
activity, which is, what, 30 years for most quinolones against gram-negatives
and gram-positives, your resistance can be predicted from there.
I
mean technology is available I think to make these decisions from the
perspective of both pharmacokinetics and pharmacodynamics integrated.
That
is what I have to say.
DR.
LEGGETT: Thank you very much.
Richard
Gesser is here, who I believe was part of the PhRMA task force with the
November meeting.
DR.
GESSER: Thanks very much. Jim, I guess invited me to speak. I am not speaking for the PhRMA group per se,
but I was part of the PhRMA group at the meeting in November, and IDSA, as
well, participated in that meeting.
First,
I just want to echo some of the points that Frank Tally made. I think the points that he made were really
pertinent to Big Pharma, as well as to Little Pharma, and the main issues, what
we face.
I am
in the Division of Antibacterial Clinical Research at Merck Research Lab, and
we are competing for resources within the company as Frank competes for
resources in the outside world. Those
resources are all used. They are used
for one purpose or another as the company decides.
I
just want to focus on the purpose of the meetings today, and the meeting in
November, I think it was Dave Cachetto [ph] from the PhRMA group who brought up
the issue of the list, and there was some debate back and forth of the value of
a list and people weren't prepared to make a list, and the list was brought up
really in the context of just sort of general guidance, acknowledging that we
are competing for resources, that drug development takes a long time, and what
we were asking for as pharmaceutical research group was more guidance and
clarity earlier on as to what was considered important in the field of
bacterial resistance.
I
think that the members of the group, I think IDSA supported this, as well, but
I don't want to speak for them here, but a lot of people felt that a targeted
list of pathogens acknowledging all the caveats associated with that list,
particularly the concept of trends over time, the limitations of the list, the
meaning of the list of people outside the purview of this group, all things
considered, that type of a list and the guidance around that list, and what
could be achieved with that list, I think part of the discussions this
afternoon, how you would, for lack of a better term, streamline or use information,
such as Dr. Schentag mentioned, PK/PD information, in vitro testing
information, to go after uncommon pathogens, and again a focused list that was
never presumed to be comprehensive entirely and always was presumed to be a
working document, something to reflect the current environment was perceived as
something that was very important in allowing us to devise development
resources, to use those development resources, and to really campaign for
resources either within our company or outside of our company if the clear
importance of developing new drugs for these pathogens was stated, I think it
would go a long way to moving this along.
One
last point. At that meeting, it was
expressed with some concern that less resources were being able to apply in
this area, and so that we were facing situations of increasing bacterial
resistance and concern in an environment where it takes a long time to develop
new products, and resources, at least new resources weren't easily being
relegated to that area of development.
DR.
LEGGETT: Thank you very much.
Is
there anyone else who would like to take advantage of the open portion?
[No
response.]
DR.
LEGGETT: Thank you.
I
think we will move on and have John Bradley address us on how clinicians use
data for clinical decisionmaking.
How Clinicians Use Data for Clinical
Decision Making - John Bradley, M.D.
DR.
BRADLEY: Thanks very much, Jim.
I
received a call from Dr. Powers earlier this week that there was another
clinician who was supposed to be giving this lecture about how clinicians use
data for clinical decision making, and since I was one of the clinicians on the
committee, he decided to ask me if I could perhaps put together my thoughts on
clinical decision making.
It
is certainly nothing unique that I do, and any clinician on this committee
could certainly give exactly the same talk, but the purpose of what I am trying
to do is to demonstrate publicly all the sources of information that we use in
actually taking care of patients, and how we take all of this data and use the
data in order to cure the patients, which is, of course, our most important
goal.
[Slide.]
We
certainly use clinical information about the patient being treated, what are
the characteristics of the patient, what are the characteristics of the
infection that we are treating. We get
organism information from the cultures including identification and
susceptibility data, so we depend on our hospitals' microbiology lab giving us
an NCCLS guidelines approved ID and susceptibility piece of information, so
that we can select from those antibiotics to which the organism is susceptible
which ones to choose for the patient.
Obviously,
the list of antibiotics that are tested by the micro lab happen to be those
that are FDA-approved and available to us.
We can certainly go to some research labs and get unapproved
investigational antibiotics tested against the organism, but the vast majority
of what we do has to do with FDA-approved therapies.
We
take into account information on pharmacokinetics and pharmacodynamics now, as
Dr. Schentag had mentioned, the toxicity characteristics of these FDA-approved
agents which are active in vitro.
[Slide.]
So,
we do clearly use the information that the FDA reviews and publishes in the
package insert and on their web site.
They certainly look at data on safety and efficacy, but they have approvals only for the
particular indications that are submitted by the sponsor, and they have gone on
record as saying that if there is an indication for which they have not been
given data, that they are not saying yes or no, they just haven't been given
data on which to make a recommendation.
So,
it is unlikely that we will get new indications for ampicillin because it is
unlikely that a group will put all the financial resources requires into a sort
of package labeling submission to go to the FDA and have them actually review
it and approve ampicillin for something, and this certainly goes for virtually
any other drug that is generic.
We
also use the medical literature for the preferred antibiotic therapy, and
certainly when the FDA approves a drug, they approve it with all the
information they have, the best information at the time of the approval, but
then a year or two or three later, unless there is more information that comes
back to them, they don't keep annually updating all of the package inserts for
every drug that they have approved.
That
is something that we find from the medical literature. We have guidelines that clinical societies
put together, like the IDSA, which is very involved in trying to tell
physicians which is the preferred therapy for which particular infections and
organisms.
In
pediatrics, the American Academy of Pediatric's Red Book Committee, the
Infectious disease Committee comes out with recommendations on preferred
therapies. There is the Sanford Guide,
which is put together by a number of very prominent infectious disease
clinicians who are internists, published clinical trials, some of which are excellent,
some of which are not so good, some of which are downright misleading, but we
are taught to evaluates these clinical trials in the literature and take the
information from these trials that is valuable and extrapolate it to each
individual patient, each individual infection that we are treating.
[Slide.]
Back
to the patient. This situation was
raised a number of times earlier today.
The immune competence of the patient is very important in whether that
patient can clear the infection. The
extremes of age, the newborn and the elderly don't have the same immunologic
capabilities as people in the middle.
The
are comorbidities, associated illnesses, sickle cell disease was raised earlier
in childhood, chronic bronchitis from the smokers in adult life, diabetes,
there is a whole host of comorbidities which impact the progression of the
infection and the ability of the host to clear this infection. These are just a few of the things. In the
time allotted, there is no way we can go into all of them.
Of
course, we like to have an examination of the patient. That sometimes gives you clues on to where
the infection is and what other problems that you may have facing you. We look at the laboratory information from
the patient which includes organ dysfunction information, which impact antibiotic
toxicity decisions.
So,
if I have two antibiotics that are equally effective, one has renal toxicity,
and I have a patient who has got pre-existing renal toxicity, I am not going to
want to use that, I will want to use the one with less renal toxicity. Then, of course, we use imaging studies, as
well.
[Slide.]
Now,
trying to put together how we take all of this information to make the
decision, I have tried to put together this Ven diagram, which includes circles
from the FDA, the NCCLS, the CDC, and the IDSA, and other clinical
organizations.
The
FDA is certainly expert at evaluating the safety and efficacy of submitted
data. That is their job. They tell me
where the drug will work and where it will not work, where to be cautious in
the group of patients for which data have been submitted to them. They also caution me on where to look out for
safety considerations, and I take their advice very seriously.
The
NCCLS looks at the organism identification, that is their job, and
interpretations of susceptibility, and they use those interpretations based on
both in vitro testing and, of three years ago, pharmacodynamic considerations.
Now,
the FDA is also historically involved in looking at breakpoints and what is
susceptible in vitro, and there are FDA microbiologists who are certainly
present at the NCCLS meetings, and it is an open forum for discussion, but the
NCCLS puts together the guidelines which virtually every hospital in the U.S.
and many in the world use in order to determine what is susceptible and what is
not.
Things
can change. The fact that third
generation cephalosporins are now considered a bit more active against
pen-resistant pneumococci.
Beta-lactam-resistant pneumococci is one example of that. Their guidelines keep getting updated, so if
there is new information on resistance that impacts my being able to use a
drug, it shows up in their documents.
The
CDC is involved in epidemiologic evaluation of pathogens, particularly
resistant ones, ones which are of public health concern, and I know the FDA and
the CDC have some interconnection. There
is probably a dotted line that goes between these two, but the CDC certainly
feeds information on organisms to the NCCLS and feeds information on epidemiology
to the IDSA and other clinical organizations.
So,
everyone is involved in this decision making process, no one can do it by
themselves. The IDSA and the other
clinical organizations that I mentioned are responsible for recommendations for
clinicians for actually treating patients for all infections with all
antibiotics, so if there is an organism
that the FDA has approved for a certain drug and a certain indication, then, if
there is another infection that that organism causes, and a clinician wants to
know if there is any data to treat this other infection, then, they will go to
these societies to get some advice on extrapolating information from what the
FDA has, again hopefully based on clinical studies which give us good, useful,
evidence-based information.
[Slide.]
Just
to give you a couple of examples briefly, if there is a 12-year-old with
leukemia and neutropenia, who has x-ray defined pneumonia, and grows a
Pseudomonas aeruginosa that is ceftazidime resistant, but meropenem and
ciprofloxacin susceptible from the bronch wash, we are supposed to decide what
is the appropriate therapy for this particular child.
So,
based on the susceptibility data, I will treat with meropenem based on the
safety and efficacy data of meropenem in pediatric meningitis. So, I take the data from just as serious an
infection, although perhaps a more immune competent host, and extrapolate with
a high dose of drug, tissue penetration, killing of organisms that I will
hopefully get a success using this drug to treat pneumonia in an
immune-compromised host.
So,
again, the FDA hasn't approved of meropenem for Pseudomonas pneumonia in
neutropenic children, I am sure, but that doesn't stop me from using the drug
in that scenario.
Now,
if it's meropenem resistant, then, I would go to ciprofloxacin, and there are
clearly even less data in pediatric populations on quinolone therapy of
Pseudomonas pneumonia, but I also use data that is published in the adult
literature to help guide me on efficacy in these certain populations, but in
kids perhaps I have to worry more about safety rather than efficacy for
fluoroquinolones, so all of these things are going around all at the same time,
and hopefully I come up with a reasonable recommendation for therapy.
[Slide.]
Another
example, and this is something that we talked about earlier with respect to
serious infections versus non-serious infections. Dr. Reller brought up meningitis, Dr. Glode
brought up meningitis where if you don't treat it with an effective antibiotic,
you don't cure the infection, in contrast to otitis media where there is a
fairly high spontaneous resolution rate even without antibiotic treatment.
This
is a real case which occurred in the pre-Haemophilus type B vaccine era, an
18-month-old with periorbital cellulitis and bacteremia, who was being treated
with ceftriaxone, and I am asked by the resident why I don't use I.V.
trimethoprim sulfa, which was available at the time, because he frequently used
the drug PO for treatment of H. flu and otitis, and the susceptibilities of
type B H. flu and non-typeable H. flu are very, very similar.
Because
no published series existed on bacteremic infections with H. flu treated with
I.V. trimethoprim sulfa, I felt very uncomfortable extrapolating from otitis
efficacy to sepsis and cellulitis efficacy, so I would not use otitis data to
convince me that I can treat bacteremic disease, whereas, I would probably go
the other direction if there were previous data on I.V. therapy of Haemophilus
in bacteremia and cellulitis, would I feel comfortable using that drug in
otitis, probably more comfortable, but I would also like to see data in otitis.
[Slide.]
So,
when can you extrapolate efficacy? If
you can successfully treat a difficult infection, you should be able to treat a
simple infection.
[Slide.]
Certainly
some infections are harder to treat based on penetration of antibiotic to the
site of infection, intra-abdominal abscesses is one case, meningitis is
another, versus infections in which there is excellent penetration like urinary
tract infections, you have huge concentrations of antibiotic in the urine, or
pneumonia where you have got excellent blood flow to the lung.
The
seriousness of the infection and spontaneous resolution of the infection, as I
just mentioned, meningitis, or a pneumonia Fine Class 5 versus acute
exacerbation of chronic bronchitis or acute otitis media where there is
controversy in the clinical community as to how important treatment is in the
first place. And then comorbidities, I
have already mentioned, healthy young adults versus neutropenia states or old
age or neonates in which you need to ask the antibiotic to do more in curing
the infection.
[Slide.]
When
can you extrapolate safety? Well, If I
have a tough infection in a patient who is not responding, and the in vitro
susceptibilities are sort of borderline, I will push the dose, and most of my
colleagues would, as well.
We
watch for toxicity certainly because there may not be as much data in the
literature on toxicity at a higher dose, but in pediatrics, where we have the
luxury of having meningitis studies where almost double the dose has been used
for a number of infections, and we have plenty of safety data, I feel
comfortable then increasing the dose in other non-CNS difficult-to-treat
infections feeling that the safety data for meningitis can be extrapolated to
the safety data in a bad pneumonia empyema or a bad pyelonephritis with a
perinephric abscess.
So,
that's one situation again where I can extrapolate safety from a severe serious
infection to treating less severe infections.
[Slide.]
So,
to summarize, we use published data from the FDA and clinical trials on safety
and efficacy for infections caused by a certain pathogen, considering the host
and location of the infection, the antibiotic toxicities, and the in vitro
susceptibilities, as well as the risk of failure, to extrapolate efficacy in
using an antibiotic which has not been previously studied for the type of
infection or the patient population that we are treating. I should have broken that sentence up into two
or three, I apologize, but all the stuff is in there.
So,
that is basically a nutshell of clinical approach that I take.
DR.
LEGGETT: Thank you, John.
Moving
right along, Ed, could you please tell us about relating clinical data from one
disease state to another.
Relating Clinical Data from One Disease
State to Another
Edward Cox, M.D.
DR.
COX: Good afternoon. It is a pleasure to follow Dr. Bradley. A lot of the principles that he has been
discussing will be parallel with some of the items that I will be discussing as
I discuss data from studies in one indication supporting studies in a different
indication.
[Slide.]
Just
to start out, and I know a number of the folks that have been present at these
meetings, but there have been a number of FDA meetings on resistance, both
meetings discussing the general topic of drug development for
antimicrobial-resistant pathogens, and then also we have had discussions with
regards to resistant pathogens in the setting of product-specific meetings that
have occurred over the last couple of years.
[Slide.]
The
topic that I am talking about today stems from one of these meetings, the
February 20th meeting, where we discussed drug development for resistant
pathogens. One of the suggestions that
came out of that meeting was to consider the degree to which a study performed
in one indication could be used to support safety and efficacy in another
indication, so that multiple studies would not be required within a
multi-indication new drug application.
[Slide.]
Just
to mention the Public Health Service Action Plan and some of the items in there
with regards to product development.
This overall approach of streamlining the regulatory process and
identifying ways to promote the development of antimicrobial-resistant drug
products is consistent with some of the action items that are within the PHS
Action Plan.
[Slide.]
I
also turn and just give a brief excerpt from our labeling regulations as to
what guidance or what information or requirements, I should actually say that
our regulations provide us with regards to the types of data that we need in
order an indication in the label.
The
regulations say that, "All indications shall be supported by substantial
evidence of effectiveness based on adequate and well-controlled studies,"
and then goes on to define these studies.
[Slide.]
You
will notice that is adequate and well-controlled studies in the plural form,
and I think the word choice here in part reflects some of the considerations
with regards to clinical trials, the reproducibility of observations that are
made in clinical trials, there are inherent variabilities that can occur in
clinical trials. There is the potential for bias both recognized and
unrecognized that may occur in clinical trials.
Chance findings can also lead to results in clinical studies.
So,
by performing more than one clinical study, essentially looking for
reproducibility, you may be able to, with a greater degree of certainty,
determine what it is that you are see in the clinical studies that you are
conducting.
[Slide.]
Today,
we have been talking mostly about bacterial infections, and we also recognize
the importance of resistance in non-bacterial infections, but we will, in fact,
focus on some of the indications here for bacterial infections.
You
will notice there is essentially a number of different indications that I put
up here. I won't go through the
abbreviations, but there is a wide variety of indications that one can study.
In
looking across these indications, you will notice that some are more related to
each other than others, as are the microbes that cause these infections.
[Slide.]
I
think really what we hope to do here today--and Dr. Bradley has helped us
tremendously I think in already elucidating some of the criterion and
principles that he uses in his practice--is really to explore the science
behind the practice of considering data that comes from outside of a specific
target indication within a multi-indication NDA.
We
have heard from Dr. Bradley some of the principles and practices that he uses,
and that serves as a very good starting point for understanding how we might
approach this problem, but we also have to recognize, too, that as we move from
the individual patient to a broader public health decision, one that would have
regulatory impact, there is certainly a higher degree of rigor that one would
be inclined to use as opposed to what one would use with a single individual
patient.
The
issue of using data from related indications is not something that is brand
new. It is actually something that is
recognized and has been in some of the prior guidances and draft guidance
documents with regards to developing antimicrobial agents.
Our
goal here is if we can clearly describe the rationale for the use of the evidence
from studies in other indications, that raises the question can we develop
criteria as to how such information may be used to support clinical studies in
other indications for the purpose of drug development.
[Slide.]
Just
to review some of the guidance documents that have provided some information
with regards to the issue of using data from other indications. The 1992 Points to Consider guidance document
discussed circumstances within a multi-indication NDA where one trial within an
indication, that is part of an overall drug development program that includes
multiple indications, might be used.
It
describes relationships between uncomplicated UTI and complicated UTI, acute
prostatitis relying upon complicated UTI, uncomplicated intra-abdominal infections,
such as mild diverticulitis, relying upon data from a complicated
intra-abdominal infection study, and then also an intra-relatedness between
complicated intra-abdominal infections and also GYN infections.
[Slide.]
Around
the same time, the IDSA/FDA guidelines that came out in 1992 and published in
CID, have some further comment on this issue that I found quite informative, so
I will just briefly mention that here.
That
is, the IDSA/FDA guidelines state that whenever possible, there should be more
than one comparative randomized study for a proposed indication. They do go on to note that, however, in
certain circumstances, a single, well-controlled study may suffice.
The
single trial may be sufficient for additional indications when a new agent has
been shown to be effective in more than one trial for a major indication
existing within the same anatomic location or organ system and caused by
similar microorganisms.
So,
I think these are, in part, some of the principles that John has been talking
about and that also are part of the criteria that I will get to.
They
do also provide some examples that are informative as to their thought
processes back then. They talk about CAP
trials and if you have a CAP trial that shows efficacy for Strep pneumo and H.
flu, then, in that circumstance, perhaps a single trial for otitis media,
bronchitis, or sinusitis would be a reasonable approach.
Then,
they go on to provide sort of a contrasting example where they talk about
uncomplicated urinary tract infections being cause by E. coli and noting that
this would not really provide much assurances to the drug's efficacy and the
treatment of bacteremia caused by E. coli.
[Slide.]
The
draft guidances 1998 describe some relationships between complicated UTI and
prostatitis are similar to what we have seen before. They also talk about concordant microbiology
data being derived from CAP or HAP studies being able to support AECB, and also
note a relationship between CAP and HAP.
[Slide.]
This
list just mentions a couple of NDAs where, in fact, these principles are
relying upon data from one indication to support another, and this is not meant
to be an exhaustive list. Certainly, a
more extensive search could probably turn up more examples, but Sporanox
injection, oral solution was improve for empiric antifungal therapy for febrile
neutropenia based upon one trial and supportive data from treatment trials of
fungal infections including treatment of aspergillosis and also esophageal
candidiasis.
Other
examples include the studies for prevention indications for Pneumocystis
carinii pneumonia and Mycobacterium avium, which were supported by data from
treatment studies of illness caused by these same pathogens.
[Slide.]
Just
to get people thinking about this a little bit, the rhetorical questions of the
relationship between CAP and HAP, same tissue site or same anatomic location,
and then a contrasting example of uncomplicated urinary tract infection support
CAP, and then complicated skin supporting HAP, and these are really just meant
to be provocative examples and really not to ask the question of yes or no, but
more to say why are people saying yes, why are people saying no, what is going
through people's minds that is leading them to say that either one can support
or one cannot.
[Slide.]
I
think the factors that people are probably considering are the things that John
has mentioned and also that we have here on this slide with microbial
etiologies, tissue penetration, severity of disease, and host in which the infection
occurs.
[Slide.]
So,
this really leads us to the proposed criteria for when data from one indication
might be able to support another indication within a multi-indication NDA. I will read through this because they are the
subject of what we would like folks to discuss, and we will talk about more
with regards to the questions.
1. The natural history of the disease under
study--and that is the first criteria--what is the spontaneous resolution rate
and what is the morbidity/mortality without treatment?
So,
this issue gets to the degree to which you can understand the treatment effect
within a particular indication.
No.
2. Factors other than the antimicrobial
which may affect outcome in a given indication, for example, in complicated
intra-abdominal infection, part of the therapy would be the surgical
debridement, and another example, ABECB, where there therapy is not only the
antimicrobial agent, but also can be corticosteroids, can be beta agonists, and
other interventions that may influence the outcomes.
No.
3. The characteristics of the study
drug. Here, for example, we are talking about the pharmacokinetics of the drug,
does it reach the site of the infection, what are the levels within those
tissues, and are there any other effects that need to be considered, such as
the pH at the site of action of the antimicrobial agent.
[Slide.]
No.
4. Then, other criteria that may
influence the data that can be inferred from a particular indication is whether
the infection is a monomicrobial or a polymicrobial infection. An example here would be enterococci in the
setting of a polymicrobial intra-abdominal infection where surgical attention
would usually be needed, and then also antimicrobial therapy directed at the
spectrum of microbials infecting, and not necessarily including enterococci
would probably affect effective therapy.
No.
5. Similar sites of infection, for
example, the lung where both community-acquired pneumonia and hospital-acquired
pneumonia would occur, so another consideration as whether one can use data
from one indication to support another.
No.
6. As Dr. Bradley has already mentioned,
too, the host effects. Certainly, there
are host differences as we move from one indication to another. For example, the patient who gets community-acquired
pneumonia may have different host factors than those patients who get
hospital-acquired pneumonia.
No.
7. Then, importantly, the seventh
criteria, the similarity in spectrum of organisms causing disease, and while
there may be some overlap with the organisms causing community-acquired
pneumonia and hospital-acquired pneumonia, there are significant differences as
one moves from CAP and HAP and gets more to gram-negative pathogens and also
more Staph aureus.
So,
these are the factors that we have come up with, that we are proposing, that we
would like the committee to discuss with regards to using these criteria to
determine when it might be appropriate to use data from one indication to
support another indication.
[Slide.]
Some
of the other considerations, and Dr. Bradley has also mentioned these, is
almost sort of a directionality of support, can a severe disease support a less
severe disease? How about vice versa?
Some
examples here would be an I.V. CAP study in relationship to I.V. HAP, and then
to contrast that oral CAP versus I.V. HAP.
Other
considerations might be the similarity of dose, duration and the
formulation. If one study uses a
different dosing regimen, how does that help us in inferring efficacy with
regards to another indication.
And
then an underlying question here, too, is also if data from one indication is
to be used to support another indication, what is the weight of evidence that
that supporting data can provide.
[Slide.]
Some
practical issues that I think deserve mention are if there is a greater
dependence on a single study in a subject indication, reliance upon other
supporting data, with regards to that single study, it is important that that
be a high-quality study, have a rigorous study design, and that it be well
performed and have very well done clinical and microbiologic endpoints since
there is a greater reliance upon that data from a single study within the
overall multi-indication NDA.
Some
other practical considerations are that within a highly interdependent program,
such a program may have less resiliency if unexpected findings are encountered
within the program. That can be either
in a supporting clinical study, for instance, if efficacy is not demonstrated
in the supporting study or that would certainly create some difficult questions
that would need to be answered about the overall indication.
Then,
it is also important that the more streamlined approach also still provide
sufficient quantity of data to adequately characterize safety, and then we
really sort of already mentioned this, and that is, in situations where there
is a more streamlined program, if an unexpected safety finding does come up, it
may be more difficult to address that within the more limited clinical program.
Then,
I have got as the last bullet, other issues here just because as we discuss
this, there may be other things that become apparent in the discussions today
for other practical issues that need to be considered within a multi-indication
NDA that is planning to use a single study within a particular indication.
[Slide.]
Then,
just to put out a hypothetical example of a dependent development program for a
drug that was being developed for more serious infections, just a hypothetical
example of two studies in community-acquired pneumonia, one study in
hospital-acquired pneumonia, and one study in complicated skin and skin
structure infections along with supportive data.
Important
to remember is that this data would provide both the efficacy data and then
should also be able to provide the necessary safety data for the drug
development program.
[Slide.]
Because
there are numerous indications, as we showed on an earlier slide, I put this up
really just to get people thinking about this question, and have sort of put down
some of the thoughts so far.
This
is not meant to limit the discussions and all, but maybe just sort of focus the
discussions initially by providing some indications where there appears to be a
relationship by organ system, and you will notice that some of the arrows are
one directional and others are bidirectional, and then also other relationships
that might be used in relating indications, and these are a little more based
on the microbiology than they are the anatomic location.
[Slide.]
What
I will do just to give folks an impression of where we are headed to is just to
run through the questions and then I will sit down and take questions if folks
have questions, and then we can move from there on into the discussion.
[Slide.]
So,
the first question and just so people know where we are headed is to please
discuss the concept of data from studies in one indication supporting studies
in a different indication.
It
would be helpful to have a conceptual discussion about this use of data from
one study supporting studies in a different indication within a
multi-indication NDA. It would also be
helpful in your discussions if you could please also discuss the proposed
criteria that are intended to identify factors which should be evaluated when
considering the evidence from studies in one indication supporting studies in a
different indication, and from the list of factors, are there factors that
should be added, modified, or removed.
Question
2. Please discuss which indications may
provide supportive evidence for a single clinical study in another indication.
Question
3. Please discuss whether data for a
more serious indication can support safety and efficacy in a less serious
indication, and are there situations where the converse could be considered,
that is, a less serious disease supporting a more serious disease.
As
we get to the questions, we can put up some other slides just to remind people
what those criteria were, but at this point, I will take my seat and be happy
to take questions.
DR.
LEGGETT: Are there any questions for Dr.
Cox?
[No
response.]
DR.
LEGGETT: Obviously, an entirely lucid
presentation. Let's hope our discussion
can come someplace close.
Committee Discussion
It
is now about 2:30, so we have a couple hours at least to come to these proposed
criteria and discuss this.
So,
why don't we just jump off with Point No. 1, and I would like to hear some
people's ideas about the concept of using data from one indication to support
studies in a different indication.
I
think that the points that were brought up in the final page, looking at the
relating indications on that final page that Ed talked about. Why don't we use those as sort of specific
example to try to flesh out what we like, don't like, or other thoughts we
have.
Since
a lot of yesterday's meeting was devoted to community-acquired pneumonia, why
don't we start with can we use community-acquired pneumonia data into the
hospital, or can we go the other way around?
Go
ahead, Barth.
DR.
RELLER: To help get the discussion
started, there was a reason that we have community-acquired pneumonia and
hospital-acquired pneumonia. Earlier, it
was lower respiratory tract infections and upper respiratory tract infections,
and I think the reason for the delineation and the arduous discussion of the
past, that to lump everything in lower respiratory tract infections did not
give sufficient delineation about severity of disease, about differences in
pathogens and that one might take easy ones and inappropriately extrapolate to
the more difficult ones led to these basic splits.
I
think the natural spectrum of organisms in community-acquired and
hospital-acquired infections, and the added complications in many of the
hospital-acquired infections also being associated with ventilatory assistance,
makes these sufficiently disparate that there is very little that one can
extrapolate in one direction or the other, not because if you had a
hospital-acquired pneumococcus, it wouldn't act like both of them bacteremic
with a community-acquired pneumococcal pneumonia, but just that the frequency
with which that happens is insufficient to put much effort into the
extrapolations with these two entities.
There
was a reason why they were split into this, and not lumped into lower
respiratory tract infection.
DR.
LEGGETT: Michael.
DR.
PROSCHAN: But what you are talking about
is not--I mean you are talking about just requiring one study rather than two,
and then using information from other similar diseases, right? You are not talking about relying entirely on
the other diseases, but on not requiring quite as strong evidence for the
particular one.
DR.
LEGGETT: That was my understanding, that
it would not be two community-acquired pneumonias studies, but one required
community-acquired pneumonia, but then if you wanted to get a hospital-acquired
pneumonia, what would you have to do, what kind of data could be transferred or
could it be transferred at all.
I
don't think we are talking so much of safety at this point although there is
some degree of that. I think at least
right now we should focus on the efficacy part of it. What sort of that sort of data can we
transfer?
Ellen.
DR.
WALD: Well, it seemed like in general
that you could feel comfortable going from the more complicated infections to
the less complicated, so if you are talking about urinary tract infection or
soft tissue skin infections, then, you established efficacy in the more
complicated, that you could feel I think assured that the uncomplicated would
do as well.
DR.
LEGGETT: By that, do you mean that if,
for instance, taking this hospital-acquired pneumonia that is more complicated,
the patient is more complicated, and it's Staph aureus, could you the
extrapolate to pneumococcus in the community?
DR.
WALD: I would make my remarks confined
to the two things I suggested, that is specifically soft tissue and skin, as
well as urinary tract infection.
DR.
LEGGETT: Go ahead, John.
DR.
BRADLEY: In look at getting a good study
for both CAP and HAP, Dr. Powers and I talked about this a little bit
yesterday. In setting up a clinical
study for, say, community-acquired pneumonia, there are certain criteria that
we have in order to enroll a patient in the study, and we are looking for a
certain percentage of bacteremic pneumonias, and certainly if there is a very
motivated investigator to get sick bacteremic consolidated pneumonias and the
number of enrollments is actually fairly small, to target that group.
If,
on the other hand, the investigators are just there to enroll every child with
abnormalities on chest film, knowing, as Dr. Wald had said yesterday, the viral
pneumonias are far more common, then the number of children enrolled in that
CAP study with viral disease, not true bacterial disease, will be excessive and
the quality of the study won't be sufficient for us to feel good, so if there
is a community-acquired pneumonia study where 10 percent of the children, 20
percent have bacteremic pneumonias, I will feel really good that that high
quality study in community-acquired pneumonia with one study in
hospital-acquired pneumonia would make me comfortable with not doing a second
community-acquired pneumonia study.
My
point in all of that is to say it's not just how many studies you do, but it is
the quality of the study.
DR. LEGGETT: I have a caveat to that. I agree that the harder your target, the
small the N you need, but on the other hand, if you are only going to use a
single study, the more comprehensive your analysis and correct your analysis
has to be as was allowed with the animal data.
It
is not the animal model, it's how your good your analysis is of that animal
model. For instance, while we were
talking about numbers of 15 or 25, that is good to know that for that
particular bug, say, pneumococcus, that we can sterilize 25 out of 25
bacteremic sick hospital patients, but unless you have got some data that will
extrapolate those 25 cases to 5,000 people that you have done Monte Carlo
simulation on, so that you know the kinetics are going to be the same in the
70-year-old liver failure, ICU patient as my 18-year-old pneumococcal
bacteremia, I am not going to buy that.
In other words, we can't extrapolate too far.
Mike.
DR.
PROSCHAN: Part of this business about
two studies is really sort of artificial.
I mean if you took one huge study and then you just broke it into two
and said, oh, here, here are two studies, I mean that shouldn't be regarded as
any stronger evidence than the one study.
It
doesn't make sense from a statistical point of view to just break it into
two. So, part of the reason it's more
convincing to add two studies is that they were done in perhaps slightly
different patient groups and maybe there are other factors that were somewhat
different. Otherwise, it wouldn't make
sense to require two.
DR.
LEGGETT: What would you say about the N
in each of those two studies? If it's
one big study, should it have the same N as the two smaller studies or, quote,
"two separate studies?"
DR.
PROSCHAN: Well, what I was saying is
like suppose you had one study and you used the number of people such that if
you cut it in half, each one of those would have high power, 90 percent power,
say.
Then,
in that situation, it is certainly not more convincing to break the study into
two and run two separate tests and say yes, look what happened than it is to
just put all the data together and compute the test statistic on the full
data. I mean it just wouldn't make sense
to do it any other way.
That
is what I am saying, that one of the reasons why it is a good idea to require
two different studies is because they are usually in different patients or, you
know, somewhat different anyway, and there are other things that are slightly
different. That makes it more
convincing.
DR.
LEGGETT: What is you required a priori
that you had to have a certain percentage of folks that would give you those
two populations, could you then have one study, you have to analyze it knowing
that your population was heterogeneous.
Does that make it stronger or weaker?
DR.
PROSCHAN: I am sorry, if you did what?
DR.
LEGGETT: You said you have two studies,
you have got one of old folks in the nursing home and one of adolescents on the
street. If you put both of those into
one study and analyzed them as one group, is that stronger or weaker?
DR.
PROSCHAN: No, that's weaker. I mean in that situation, to me, that
situation is different because I want to know separately whether it is working
in both groups. You put them all
together, you could increase the variance to such an extent that you may not
see anything.
DR.
LEGGETT: And if we use one study in a
hospitalized pneumonia with a larger study in community, and then try to go
across it, aren't we doing the same thing?
DR.
PROSCHAN: If you go across?
DR.
LEGGETT: If you try to use your data
from your community-acquired pneumonia to then tell you something about
hospital-acquired pneumonia, isn't that doing the same thing?
DR.
PROSCHAN: What I would do, to me it
seems like a reasonable approach is you already have some results on community-acquired
pneumonia, and I would still require a study in hospital-acquired pneumonia,
but then if I had that study that was positive, then, I would also try and use
the information from the community-acquired, as well.
So,
I think you still, you know, you have got to have a study that shows it in the
particular one that you are interested in, but perhaps not two. I mean you could borrow the evidence from the
other one to help corroborate the results.
DR.
LEGGETT: Dave, you look like you want to
say something.
DR.
BELL: I just wanted to add that I am not
in disagreement with the general tone of this, but I think there is value in
two studies that goes beyond just different population groups studied. I mean the investigators are different, the institutions
are different, geographic region of the country, of the world is different. It
adds a certain robustness in terms of whether there might be biases.
DR.
LEGGETT: You knew that was a surrogate
for all variability.
DR.
BELL: Okay.
DR.
PROSCHAN: I agree with that. I just was struck, one time I reviewed
something where they said yes, we have done these two different protocols and,
you know, they were done exactly alike, they had the same investigators, and to
me, they did what I said you probably shouldn't do, you know, they basically
just cut one study in two, and that is not more convincing. But I agree with you that all those things
are important, the fact that, you know, there other differences, as well.
DR.
LEGGETT: Alan, you looked like you
wanted to say something.
DR.
CROSS: We saw yesterday, I think that
there were four control studies presented off of the same indication, and one
of the four was markedly at odds with the other, so I do think what everyone
else has been saying.
First
of all, that no studies are done exactly alike and that there is a greater
confidence when we see that there is at least more than one study going in the
same direction, and also in terms of comparability, I agree with Barth that it
is very hard to extrapolate hospital-acquired to community-acquired because of
the obvious multiple differences between the two syndromes.
DR.
LEGGETT: Could you elaborate on what
kind of differences you are talking about, differences in the host, not just
different pathogens?
DR.
CROSS: First of all, the organisms and
comorbidities, and therefore perhaps how the drug has to be delivered.
DR.
LEGGETT: Orally rather than I.V., you
mean.
DR.
CROSS: Yes.
DR.
LEGGETT: In terms of the analogy that
Ellen made about going from complicated to uncomplicated, wouldn't you think
that that same analogy could be from complicated to hospitalized sick patients
to folks with less, quote, "complicated"?
DR.
CROSS: If they have the same organisms,
but I don't think what we are talking about are two completely different
organisms, but, in general, if one were to have a more severe hospital-acquired
pneumonia and extrapolated to perhaps lesser severity, that is obviously
acceptable.
DR.
LEGGETT: Go ahead, John.
DR.
POWERS: Alan, let me ask you for a more
specific example here, because clearly, there are different pathogens between
community- and hospital-acquired pneumonia, but suppose the drug sponsor came
in with, say, a carbapenem type drug, which looked like it had, in the test tube,
activity against Pseudomonas, Acinetobacter, and Strep pneumo, H. flu,
Moraxella, and the common ones, and they did first a community-acquired
pneumonia trial, and they got, unlike what we saw yesterday, a whole lot of
Fine Class V people in there, severely ill people.
This
is probably assuming this is going to be I.V. drug. Then, you get, as John pointed out, a
high-quality, hospital-acquired pneumonia trial, one of them, and assuming it
works, because that's the other issue, what we saw yesterday. If your one trial was that one gemifloxacin
trial that didn't work, you have got a problem.
But
suppose that that trial actually shows it works, are you convinced by that one
hospital-acquired pneumonia trial, based on what you saw in a community-acquired
pneumonia trial?
DR.
CROSS: Well, I think a real wildcard is
certainly in hospital-acquired pneumonia, one of the variables you don't have
in community onset is the appliance, the endotracheal tube, and the situation
is, first of all, that it is much more difficult to clear organisms in the
presence of a trach tube.
But
the other aspect of it is that, as I see it, there is a lot of disagreement in
terms of just defining the bacteriology of ventilator-associated pneumonia, for
example, is Staph epi truly a pathogen, and if so, do we have to evaluate a
drug efficacy there, which you would never do for community onset.
DR.
POWERS: I guess what we are
getting--maybe if I can make it clear--we are not saying that you do no trials
for hospital-acquired pneumonia, that is not even on the table, so let me
phrase the question another way.
Somebody
does a CAP trial for this carbapenem type drug or let's say they do two of
them, like Ed used in his example, and
then they have one hospital-acquired pneumonia trial, and it works, and the
drugs works, and it is a well done trial.
What
is the second hospital-acquired pneumonia trial going to tell you?
DR.
CROSS: You mean aside from the
reproducibility of that.
DR.
POWERS: Exactly, because that is the
question we are asking. So, you have got
two CAP trials with a drug and it works, and now you have got one
hospital-acquired pneumonia trial, and what we are asking is assuming all those
things, that is a well-done trial, and that the end results show the drug is actually
effective and safe, what does the second trial in that indication actually add
to that?
Now,
there are a lot of ifs in there, that is what I am saying, and, of course, the risk there, too, if your
one HAP trial and the drug fails, you have got a problem.
DR.
CROSS: If what you are saying is on the
community onset one, that you have sufficient number Klebsiellas, Pseudomonas,
et cetera, then, I might not have as much difficulty, but it seems that most of
the drugs which we have evaluated for CAP are really looking at the atypicals
plus Strep pneumonia, so I think it depends how much emphasis you wish to place
on, let's say, gram-negatives, in that situation.
DR.
POWERS: So, I guess what I am hearing,
then, to sort of summarize that, would be that perhaps in a single
hospital-acquired pneumonia trial, you would still need an adequate number of
organisms more commonly seen in HAP than community-acquired pneumonia to give
you some confidence of what was going on.
So,
that would go to sort of the size of the HAP trial and again the quality of the
data that you are getting.
DR.
CROSS: Well, again, it might be size,
but I think also what we have been discussing is, is there an intrinsic value
to having a study done under one protocol by certain investigators reproduced
at least a second time, and I should say it does not have to be a huge trial if
the patients included are, as we say, informative.
DR.
LEGGETT: Keith.
DR.
RODVOLD: Actually, your comment in the
beginning is what I actually observe out in the field, is that most of the
pharmaceutical companies, no matter what kind of compound it is, go two CAPs
and come to one HAP, and despite the
compound, it is probably better for HAP than it is for CAP, because when they
get through and get their numbers for safety, as well as build up a database
off the CAP and then make the flip to HAP, and kind of come through smaller.
When
you look at those pathogens, and I think the message came up pretty strong this
morning, and I agree, that there is nothing in the pipeline for gram-negatives,
and really nothing, that if it was in the pipeline, has really been developed
for serious gram-negative infection indications.
If
it has got enough gram-positive coverage, which they almost slip in on the
compound today, so they can get into the community indications first, that is
where they go, and here is no incentive for them to kind of come the other way.
My
point is that I think you need to think, I agree with everything, that the
diseases are different, the patients are different, that there is no doubt that
the bugs are different, but if you really want to be serious about getting
people to develop drugs and gram-negatives, and get nosocomial type infections
on board, you have got to do something to make them come that way, because they
are not coming that way, and they are not going to come that way at the price
of drug development and delays they could face.
So,
that is where you are going to have to get the caveat or carrots out there to
get them to come and to hopefully develop drugs that give us that, because I
don't think there is any incentive for them to do it, and that's just what I am
constantly seeing, and I think the example you put is one that is out there
already, a big carbapenem, but it doesn't have nosocomial, and they are teasing
now with how to get it in CAP guidelines.
I am like going really.
DR.
COX: It sounds like what I am hearing is
that people are thinking really in terms of the criteria and essence, but it seems that efficacy within the lungs
is not enough, there is reservations about using that information derived from
a CAP study with regards to HAP, and it sounds like the point there is
actually, really to the microbiology and the host factors.
So,
those are a couple of the criteria that we have there, but it sounds like there
is some reservation with regards to that use of supporting information from,
say, two CAP studies to a HAP study.
Do I
characterize that correctly?
DR.
LEGGETT: Especially the lack of
bacteriologic data that seem to be coming of CAP studies.
John.
DR.
BRADLEY: I am still supportive of one
CAP and one HAP, and there is an example that I can give you right now. We are in Phase III trials of ertapenem with
CAP, and ertapenem is a very potent antibiotic, and I don't know if I am going
to use ertapenem for CAP for the routine, run-of-the-mill well child that comes
into the hospital with pneumonia, assuming the drug is approved.
So,
I don't want to do two CAP studies with ertapenem when I see the value of the
drug being one for hospital infections and outpatient infections. So, I don't you to ask the company to do
extra studies in an area where, at least in pediatrics, it may not have its
strength.
So,
a CAP study, which is one, well-done, well-powered with high-quality study,
where the HAP study, I think will help me.
Now,
the gram-negatives that we are talking about, that cause HAP, if there are
other supportive data in treatment of those gram-negatives in other tissues,
such as complicated urinary tract infections, I will feel better about using
the drug for those gram-negatives when they appear in the lung for HAP,
especially if I have CAP data to show that I have got good drug penetration,
and we are actually doing a complicated UTI study, as well, with the same drug.
So,
I use drugs, the studies, to help complement my confidence in using the drug
for pathogens in the lung when they come from another tissue site.
DR.
LEGGETT: Mark.
DR.
GOLDBERGER: Just to follow up what Drs.
Rodvold and Bradley said. I think we
would agree that in the perfect world, we would want, for each indication,
multiple studies. I think everybody
would feel most comfortable about that.
But
we live in a world, of course, that has various constraints. One of the constraints is that it takes a
certain amount of resources in order to perform all these studies. So, the question really we are sort of asking
is, in part, in order to encourage and facilitate the development of new
antimicrobials, you know, recognizing the fact that companies have to make
decisions about how to apply their resources, what are the things that we can
do to sort of expedite the development program, and the big clinical trials are
ultimately fairly expensive to perform.
So,
we are sort of asking this question, not in the perfect world, but also in the
constrained world in which we live, to try to understand what things might
conceivably be reasonable.
We
acknowledge, of course, this issue that was raised, that the microbiology in
HAP is different than the microbiology in CAP, and how much overlap there is
depends on a lot of factors, but clearly it is different as well as the
patients themselves.
Now,
we have, for instance, the opportunity in a multi-indication development
program to also, for instance, explore complicated intra-abdominal infection,
which gives us the opportunity to look at fairly sick patients over a wide
variety of ages, who will have significant gram-negative infections.
Now,
arguably, surgical intervention is a component there, and that is an issue, as
well. We also have the opportunity to
look at complicated skin including diabetic infections, again where there are
issues of significant gram-negatives.
Now,
are these perfect surrogates, for instance, what goes on in the lung? No, it depends in part on how much
information you have acquired about comparative tissue levels as part of your
development plan, but we are faced with dealing at one level with a somewhat
constrained environment, and the question is what can we do with that
environment recognizing that this is less than what we would normally do
perhaps in the perfect world, and in those circumstances, what is our level of
comfort and what is the things we really want to sort of look at and think
about in order to make reasonable accommodations.
DR.
LEGGETT: Mike.
DR.
PROSCHAN: We have been making it kind of
simple here by considering only HAP and CAP, but there might be several related
bugs, and the question is should you take into account information on the other
ones. I think definitely, you would have
to say yes.
I
mean if you found one clinical trial that showed efficacy for HAP, but all the
other things that you think ought to be similar, the drug doesn't work for,
then, you would probably want to see another study. On the other hand, if it is consistent, all
four are showing the same thing, then, that might be a situation where you
would be happy with just the one.
DR.
LEGGETT: Again, I come back to my point
of how good the study is. My view of
studies of complicated skin and soft tissue infections close up is it looks
pretty bad. You can swab somebody's open
foot ulcer and its complicated skin and soft tissue, but that is not at all
what I would worry about if I was treating somebody with nosocomial pneumonia
who had the same pathogen in their lung.
Then,
the question I get to is can we redefine the criteria of how many people or
what kind of person you have got, and how much has to be bacteriologic hard
data in your CAP trial.
DR.
POWERS: Let me switch out of indications
where this might even be more relevant, because this committee has discussed
this only a few months ago.
If
you take a look at one of the things we have on the bottom there, of sinusitis
compared to otitis media, now, those are two infections where the organisms are
almost identical for those things, but we could make the case of what kind of
quality data do we see for those kind of indications.
As
you are saying, Jim, when one is going to use those to support the other, does
the kind of clinical-only trials that we saw in the past, with no microbiology,
or a microbiology trial with no clinical information along with it that is open
and non-controlled, what does the committee think about that if we are then
going to use that to relate one disease to the other?
DR.
LEGGETT: I don't like it.
DR.
RELLER: No numbers can make a lousy
study a good one. I have no problems
whatever extrapolating from otitis media to sinusitis and vice versa if we have
got sinus taps and tympanocenteses with microbiology and eradication of the
organism.
Coming
back to CAP and HAP, it is not that they could never be extrapolated one to the
other. It is just that the probability
of having comparable organisms is so small, and even if one had a drug that was
active against Enterobacter in HAP, and it was active against the Pneumococcus
in CAP, I am not willing to extrapolate drug X's data for the Pneumococcus to
the Enterobacter in HAP even though they are both susceptible organisms to this
putative compound that you mention.
When
we come to two studies/one study, I am actually much more interested in the
numbers that I know that they have the entity, the bacteremic pneumococcal
pneumonias in CAP, the ones that had an expectorated sputum where the organism
was seen on Gram stain, and it was grew and it was devoid of epithelial
studies, the HAP studies that have quantitative cultures obtained by endoscopy
and bronchial brush.
I
mean those where you have got the best possible chance to be sure of what you
have got, and then those, of course, accompanied by bacteremia, to me, mean a
lot more, and these clinical studies that we have had in the past with otitis
and sinusitis, they don't tell us very much, and they certainly don't tell us
very much with the kinds of organisms that Dr. Jorgensen described earlier.
DR.
LEGGETT: Keith.
DR.
RODVOLD: I agree with Barth in the type
of patients, and I think the agency themself has used this as an example. It's the levofloxacin data, when that came
through to us. I was on the committee,
Barth was there, and what was convincing was the story, the whole story. I mean they had a reasonable number of
patients, the quality of the patients, and what they had recovered, but they
also had the kinetics, the dynamics, the in vitro models with it, and the story
was very consistent to get into a smaller group of numbers of quality people,
and it rolled along.
What
I would throw on top of that these days would be what Jim brought up, was doing
some simulations on top of that information to kind of project out of the worse
scenarios, the people that have a very fast clearance to a slow clearance, to
someone with a high MICs to low MICs, to again give people comfortability
levels, just like what they have been doing at NCCLS more recently of 80
percent of the time, you are going to hit the target even if it's someone that
is a poor eliminator or a fast eliminator.
I
think that building that whole story around one good study that has good
quality patients that are really sick, that have the real pathogens, is more
convincing that two trials that have kind of some numbers, and I think that is
still the best example you have to share with people.
DR.
LEGGETT: Mimi.
DR.
GLODE: I just wanted to comment on the
issue of trying to establish safety and efficacy in the same study, so sort of
torn between we want to enroll a lot of people, so we have some safety data,
but then really, often inadvertently, if you will, contaminating the population
and sacrificing quality of the study.
So,
particularly, I know it is very hard for everybody, whether in pediatrics or
internal medicine, but community-acquired pneumonia, trying to figure out who
has got a viral respiratory disease that is going to get better no matter what
you give them, who has got mycoplasma that is going to get better no matter
what you give them, and who actually has bacterial pneumonia that presumably
will definitely get better faster and needs an antibiotic, you know, means the
best microbiology, it means pneumococcal urinary antigen, as Barth mentioned
yesterday, potentially, I mean quantitative CRPs, I think there are better ways
to narrow that population and then study that population, because if you
inadvertently contaminate them, you create this effect of making the drug look
fabulous in this population, and that is not the critical information you
really want.
So,
as long as you are inadvertently contaminating them, it is elevating the
efficacy of the drug inappropriately and misleading everybody.
DR.
LEGGETT: Ellen.
DR.
WALD: I think the infections in which
you would have the greatest ability to extrapolate one to the other are the
ones in which the microbiology is the same, and so, you know, acute sinusitis
and acute otitis media are identical for all intents and purposes.
Some
have made the observation that the middle ear is a paranasal sinus, and I think
there is truth to that when you think about the eustachian tube as a sinus
ostea.
I
think a question that you could ask from there is how similar is that
bacteriology to the microbiology of acute exacerbations of chronic bronchitis,
and then at least in children, for the bacteriology of a community-acquired
pneumonia, which, of course, is something we don't exactly know what the
bacteriology of community-acquired pneumonia is in children short of the
pneumococcus, because that is the only thing that we grow from blood cultures
in pleural effusions, although it may not be the only cause of bacterial
pneumonia.
So,
I think where you have similar microbiology, you have the greatest ability to
extrapolate, and I think, though, it puts a tremendous burden on the quality of
the first study that you do for any of those for it to be really high quality,
and to have as much microbiology as possible.
DR.
POWERS: Could I ask a follow-up question
about that, because you named three respiratory diseases and two of them are a
little different, and that for otitis media and sinusitis, they are both
normally sterile body sites where we can get that microbiology by
tympanocentesis or sinus puncture.
On
the other hand, acute exacerbations of chronic bronchitis is a disease where,
if you culture those people when they are not having exacerbations, you are
going to find those bacteria there, as well.
So,
does the certainty of diagnosis of what that microbiology means also play into
part of this?
DR.
WALD: Well, I think if we are willing to
suspend certainty for a moment, since we really talked yesterday and I think
everybody was sincere about the need to do an antibiotic versus placebo study,
but if for the moment, we accept that it is a real entity that is caused by
bacteria at least in some proportion of the cases, then, microbiology is really
very similar to the others. Maybe there
is a little shift in proportion of the organisms, but they are really pretty
much the same organisms.
DR.
LEGGETT: Would you be willing, assuming
that acute exacerbation of chronic bronchitis or bronchitis, assuming
antibiotics help, would you be wiling to go from community-acquired pneumonia
to that indication with the one study?
DR.
WALD: Yes, I would, because again, I
think going from the more complicated to the less complicated is a direction
that has an ease associated with it. So,
in a more stringently, better defined infection, i.e., CAP, a drug proves to be
effective, then, I think that one could comfortably conclude that in a lesser
infection, acute exacerbations of bronchitis, that it would perform equally
well.
Again,
if we have bacteriology that includes non-typeable Haemophilus and Streptococcus
pneumoniae as being probably the major players in both of those infections.
DR.
POWERS: Let me extend that a little bit,
asking about the directionality question.
So, if you had otitis or sinusitis, that might be supportive of acute
bacterial exacerbations of chronic bronchitis.
I am
assuming that these trials are doing at different times because a lot of what
we see is they are done simultaneously and we can use them to support each
other, but suppose the ABECB trials gets done first, how supportive do you
think that is in the other direction of, say, sinusitis or otitis media?
DR.
LEGGETT: None.
DR.
POWERS: Because that is the stuff we are
dealing with is, you know, is there a directionality to this, and the CAP one
is clearer, better, ABECB is a little different.
DR.
LEGGETT: Jan.
DR.
PATTERSON: I was going to say I agree
with Ellen, and that I think you can go from CAP to ABECB, but not the other
way around, and also from acute bacterial sinusitis to acute otitis. In adults, I have a little reservation about
going from otitis media to acute bacterial sinusitis because I think adults
have staph sinusitis sometimes, but if you had an acute otitis media study and
you knew that the compound had good staphylococcal activity, then, I might go for
that.
That
kind of gets to the point of, you know, with some of these resistant organisms,
they have had sort of pathogen-directed indications like VRE, bacteremia, and
that kind of thing, and I think if you had an antibiotic that was successful in
treating bacteremia, that it would most probably be successful in treating UTI
and lesser sorts of things, but I don't know how much you want to go for
pathogen directed indications.
DR.
LEGGETT: People are trying to get
multiple indications. If they are only
trying to get one, is it still two studies and supporting data?
DR.
POWERS: Yes.
DR.
LEGGETT: I just wanted to make that
clear.
Could
the two studies, one is controlled, and could the other be one of these
enriched pneumococcal antigen, or do they have to be controlled, blinded, the
variability problem?
DR.
POWERS: That goes to the reproducibility
of the information. Whether one could
then do two studies and then some other kind of open-label trial trying to
accrue more resistant pathogens might be one way to go.
DR.
LEGGETT: Barth.
DR.
RELLER: One example of this question
about one study/two studies, if you had a good efficacy demonstrated for the
pneumococcus Moraxella catarrhalis, I mean the respiratory pathogens with the
community-acquired pneumonia study, and one had a single acute exacerbations of
chronic bronchitis that was placebo-controlled, I don't think anybody would
have any trouble extrapolating.
I
mean that would be one nice example of a single study would be all you would
need if it was a good one, on the one side, and it was a good one on the other,
and then the transfer of the information.
I would like to see more of those.
DR.
POWERS: I think one of the issues we are
trying to get at is what I think I heard yesterday a couple of times was what
is the incentive for anyone in industry to go out and do a placebo-controlled
study of acute bacterial exacerbations of chronic bronchitis, so in this way,
it sounds like this might be some incentive if it streamlines the drug development
process in some way.
The
other issue I think that we didn't talk about much yesterday is a
placebo-controlled ABECB trial has fewer patients in it than a non-inferiority
trial of ABECB does, therefore, there is two benefits to a company doing this. Do I think we are going to see this? I am a little skeptical from what I have
heard, but at least we can at least hold out that there is some benefit to
industry to actually do things this way.
If
there is not, why should anybody do this?
DR.
RELLER: Yesterday, I would have to pull
out the books, but, what, 2- to 300 in three different trials with acute
exacerbation, or were there four? There
were three or four trials for acute exacerbations of chronic bronchitis.
DR.
COX: You mean in yesterday's discussion?
DR.
RELLER: Yes, yesterday. I mean at least three, three, four or
five. Let's take four trials, 250, 300
patient apiece, I mean one good trial would have I think given us more useful
information than all of the material that we wrestled with yesterday with acute
exacerbations of chronic bronchitis.
DR.
POWERS: You are hitting on my pet topic
here, so I have another question for the committee related to this. So, if it's okay to expose 800 people to a
non-inferiority trial in ABECB, one of the things we hear is it is unethical to
do a placebo-controlled trial.
Well,
how ethical is it to expose all those people if we don't even know if the drugs
have any efficacy in that disease?
DR.
LEGGETT: Correct, but they are not going
to die. I think that people draw the
line at when you are going to die.
DR.
POWERS: I am trying to address the
question of why is it unethical to do a placebo-controlled trial in ABECB.
DR.
WALD: Who says that it is unethical?
DR.
POWERS: Ever since we had this discussion
in November, we have tried to ask drug sponsors saying based on what we heard,
that we think that these trials should be placebo-controlled. No one has expressed a willingness to do so,
and one of the reasons we hear is that IRBs have a problem with this and that
it is not ethical or supposedly not ethical to do a placebo-controlled trial in
this disease.
DR.
LEGGETT: Barth.
DR.
RELLER: What a wonderful opportunity for
a sponsor. We have got the Infectious
Disease Society of America participating in the meeting saying that
placebo-controlled trials are necessary, and even the Institute of Medicine
saying this is something that should be brought up to the NIH for funding
because this is important.
I
mean I would think that there are sufficient published consensus bodies
experts, I mean it should be a slam dunk within IRB. I mean we have emphasized here the
tympanocentesis study with the demonstrations, the taps, that it can't be done,
the amount of useful information in what the potential benefit of knowing what
somebody actually has as opposed to the pitfalls of empiricism in a world of
unexpected resistance, I think the time has never been better to tighten the
science and thereby achieve also economies of having more useful information
involving smaller numbers.
DR.
PROSCHAN: Would you expect the drug
companies to say we don't want to do that because our drug might not be any
better than the placebo? Of course,
there is an incentive to say it is unethical.
DR.
LEGGETT: Ellen.
DR
WALD: I think it may help. You know, there are certainly some published
statements from recommending agencies suggesting that these things are ripe for
investigations, and I think the timing is right, but I have to say that the
IRBs now are particularly skittish.
I
think that they are feeling a lot of pressure because of the kinds of things
that have recently been reported in the press about mistakes of protocol
implementation, whatever, and we just had an experience at Pittsburgh where, in
fact, our IRB has declined approving a placebo-controlled trial of acute otitis
media, and we are going to be sending it to the FDA to get their ruling on
that.
I
think that is despite the fact that, you know, there is a lot of media now
looking at watchful waiting as a strategy.
So, I think that maybe in the minutes of this meeting, if we can make a
formal statement about how important these studies are, that it will create a
sense of equipoise, which I think is what is necessary to engage in any of
these kinds of investigations.
I
think that we can, in fact, state that equipoise, because I think we don't know
the answer.
DR.
LEGGETT: Keith.
DR.
RODVOLD: I agree, that, you know, being
a past IRB member plus dealing with the IRB constantly, that every IRB is its
own animal basically, and the only way you get through it, especially where a
lot of people do trials, they go through IRBs that are way different than the
ones that I think most of the people sitting around this table go through as an
IRB, and you would need to not only gather the literature, but I think you
probably would have to make a statement that would go right in the packet.
That
does lend credence, a lot of credence, in areas of untouched territories or
uncomfortable territories, and I can tell you one of our IRBs, when you bring
up placebo-controlled, are just like what Pittsburgh is running into, it's
almost a no go until you can just really show them with convincing data and
convincing endorsement from the Federal Government that this is a possibility.
DR.
LEGGETT: Go ahead, John.
DR.
POWERS: Having been on an IRB myself, I
agree that it is the quality of the data that gets presented to the IRB that
sways them, and one of the things that always comes to my mind now when we talk
about levels of evidence is the trial that was done on hormone replacement
therapy in women that was published just last year.
Loads
of observational data saying that that therapy actually prevented
cardiovascular disease, one very well-done placebo-controlled trial shows it
does not, and those are the kinds of things that I think are convincing to
IRBs, look, we have all these trials done in the past that prove absolutely
nothing to us, we want to do a kind of trial like the hormone replacement trial
to answer this question definitively.
Jim,
could we maybe look at some of those criteria?
DR.
LEGGETT: Sure. Don wanted to say something and we will do
it.
DR.
PORETZ: In certain areas like
cardiovascular disease, you look at endpoints with events like how many
myocardial infarctions you are going to have or how many deaths you are going
to have if a person does or does not take a certain drug.
In
infectious diseases, when you are doing drug studies, antimicrobic studies, who
determines the total number of patients for validity of a study, is the
pharmaceutical company and their statisticians, is it the FDA and their
statisticians, who determines?
DR.
POWERS: That is something we usually
work on together and it usually depends upon what the endpoint is and how
effective you estimate that your drug is going to be, and then it gets into the
dreaded delta issue of how effective you want your drug to be relative to
whatever control that you are happening to use, but that is usually something
we talk about, that the FDA and the pharmaceutical sponsor, we talk about
together.
DR.
LEGGETT: So, what we are saying
basically is if we are going to be able to change things and improve the single
trials, that you guys are going to have to require more stringent criteria on
your part.
Ken.
DR.
BROWN: If I understand the discussion, I
am a little uncomfortable with the idea of CAP to HAP or reverse, unless we are
absolutely stringent on the organism, be a case-by-case by organism. The pathology of Pseudomonas pneumonia is so
dramatically different from the pathology of Pneumococcal pneumonia that I
can't conceive that we could let anybody get a claim for both regardless of
where they came from.
I
think a parallel exists in my discomfort with otitis media and sinusitis. After the first or second bout of sinusitis,
I believe that you no longer have acute sinusitis, you have acute exacerbations
of chronic sinusitis.
Joe
Fredericks showed in around 1964 that if you do cultures for obligate
anaerobes, and not just facultative anaerobes, you always get anaerobes in
those sinuses, which means to me that the drainage procedure may be more
important than the antibiotic in those cases, but certainly we shouldn't be
using antibiotics which don't have anaerobic coverage for those people.
DR.
LEGGETT: I think one would have to
specify there are big differences between adult and pediatric populations in
terms of sinusitis.
Here
are the proposed criteria. No. 1, the
natural history of the disease under study - what is the spontaneous resolution
rate and what is the morbidity/mortality without treatment? This is where we have been talking about
acute exacerbation of chronic bronchitis.
Are
there some others in terms of we are talking about various different models
where that might apply other than the otitis that we have just mentioned?
Go
ahead, Ed.
DR.
COX: One of the things that might be
helpful would be this morning, some of the criteria were actually ranked as far
as level of importance, and I think that might help us get a better feel. I think we had some discussions about where
there are criteria that are more important than others at least from the
discussions we had going on here.
That
would actually be helpful to us, I think, if we had some discussion of the
criteria, which of these are of the most importance and which ones are of
lesser importance.
DR.
LEGGETT: The diseases that we get the
most irrelevant data on are the ones that have the fewest hard endpoints, and
that is the upper respiratory tract type problems. That, to me, is probably the strongest
argument for a placebo-controlled trial in a disease of that nature.
Don.
DR.
PORETZ: Another example of 1 would be
chronic bacteriuria, chronic urinary tract infection in elderly women where
most people now would not treat asymptomatic bacteria. I mean you can put them on an antimicrobic,
get rid of the organism, just like chronic bronchitis, it means nothing.
DR.
LEGGETT: What about something like skin
and soft tissue infections, whether it's complicated or uncomplicated, we are going
to let clinical data go where we can't get bacteria? That is another example of two things that I
can think of where we don't really get reliable data, but we know from antibody
studies that 90 percent of them are group A strep, at least in uncomplicated.
What
kind of numbers do we need for that? Are
those going to resolve by themselves, does anybody think?
Go
ahead, Alan.
DR.
CROSS: Not with group A strep or Staph
aureus.
DR.
LEGGETT: Or Staph aureus.
DR.
CROSS: But perhaps I can take this opportunity
to ask a question, and that is, we heard from the pharmacokineticists and
dynamics folks that if we had an AUC of greater than 100, it is highly
predictive of efficacy, so I am just wondering, in the case of like a skin
infection, if we actually were able to measure the antibiotics in the skin and
actually calculate how much of a dose actually gets in the skin.
Can
that type of data be extrapolated to other organisms?
DR.
LEGGETT: So, in other words, the
question is sort of will you guys allow in vitro or in vivo model
extrapolations.
DR.
POWERS: That is actually No. 3, the
characteristics that is up there about looking at the pharmacokinetics of the
drug. How to use pharmacodynamics is
something that we have been discussing internally and that got brought up in
November, and the FDA has an internal exposure response working group, which is
actually trying to look at this information of how can we actually apply some
of that data.
DR.
COX: I think, too, I mean we are
focusing here today on clinical data and really the reliance and inference that
can be drawn from other indications, so I think it is more clinical that we are
talking about here today.
DR.
LEGGETT: To finish up with the natural
history stuff, does anybody here believe that prostatitis or urinary tract
infection is going to go away by itself, and what are we going to do? Uncomplicated urinary tract infection, you
know, post-coital cystitis, do we need placebo control is what I am saying or
do we have to have controlled data? I am
just making sure that we flesh this whole thing out before we go. No.
The
only thing I can think of unless somebody tells me otherwise that we are going
to have placebo control is that upper respiratory tract.
DR.
POWERS: But our real question is how
they would be supportive of another disease.
So, I guess what I was hearing was acute bacterial exacerbations of
chronic bronchitis trials wouldn't be supportive of anything else unless you
did a placebo-controlled trial.
DR.
LEGGETT: Right. That is the lowest on the totem pole,
everything is above that.
A
question that sort of jumps back in terms of what do you propose. If you have a very good, tight puncture of
the ear trial with data, and you have one puncture trial of the sinus data in
kids, can you use them back and forth, or do you need two in the ear and then
one in the sinus?
If
we have just made the argument that they are the same, why do you need two in
one and in the other except for the best possible world validation?
DR.
COX: I think it gets to the issue of
level of evidence, and having the one indication or anchoring the initial
indication in a couple of studies, and then moving on to use that information
to support other studies, so it is all level of evidence question, and we have
had some discussion about the number of studies, one big study versus smaller
studies.
John
mentions another good point, too, and that is, you know, accruing sufficient
numbers of patients in order to be able to adequately characterize the safety
of the drug, too.
DR.
LEGGETT: Right, the same globalization.
Jan.
DR.
PATTERSON: Just in terms of priorities,
you were asking about priorities. I
think one of the things that have spent a lot of time talking about is that No.
7, similarity in spectrum of organisms causing disease. I think I would put that pretty high, like
towards No. 1.
Then,
No. 5, similar site of infection, you know, respiratory versus urinary versus
skin and soft tissue, complicated versus uncomplicated, we have been talking
about that, too, so I think that would also be pretty high up, maybe No. 2.
I
would see those two as being a couple of the more high-priority ones.
DR.
LEGGETT: So, what you are saying, for
No. 5, was we don't really seem to like the CAP/HAP thing. You are saying that urinary,
complicated/uncomplicated, skin, complicated/uncomplicated, and how about urine
and prostate?
DR.
PATTERSON: Complicated UTI.
DR.
LEGGETT: Yes, complicated UTI.
DR.
PATTERSON: Complicated UTI, then, I
would go for prostatitis, yes.
Go
ahead, John.
DR.
BRADLEY: In extrapolating between the
same site of infection, but different scenarios, like HAP and CAP, knowing that
they are different types of organisms, in my suggesting that all you would need
is one study of each, the implication was that you would need to study a
certain number of Pseudomonas infections either in that HAP trial, so that you
would know that it would work in Pseudomonas, hospital-acquired pneumonia, or
have just a few in hospital-acquired pneumonia and then Pseudomonas in another
complicated tissue site that you would not expect any spontaneous resolution,
so some sort of complicated urinary tract infection, hospital-acquired urinary
tract infection, or deep surgical wound infection, a mediastinitis.
There
are certainly situations where you can collect information on the drug's effect
on the organism, so what I am trying to build is taking a certain amount of
information on efficacy at a tissue site, but requiring a certain amount of
microbiology that is either from that site or a comparable site.
So,
if you can treat Pseudomonas or Enterobacter or Klebsiella in a complicated
intra-abdominal infection, because even though you require surgery, the
antibiotics are part of the whole treatment process, if I can get efficacy data
in those pathogens in another tissue site, I will feel comfortable
extrapolating into a pneumonia site and requiring fewer of those cases in a
pneumonia.
You
had in the other slide complicated intra-abdominal infection towards
complicated skin and skin structure.
Well, you don't get Staph aureus very often in a ruptured appendix, but
it's a deep tissue space where there is a low pH, lots of white cells that
requires drainage, so the same thing would be true of a cervical adenitis that
requires drainage caused by staph in terms of the environment, but the
organisms would be different.
So,
I wouldn't go from intra-abdominal into complicated skin and skin structure
unless I had data on Staph aureus supporting skin and skin structure, and where
you would get that other data, I don't know, certainly not in intra-abdominal
infections.
Then,
you have got complicated skin and skin structure supporting complicated
intra-abdominal, and again the same concept is there. The organisms are completely different even
though the types of tissue environment would be similar, both deep tissue, both
requiring drainage.
DR.
LEGGETT: To follow up on that, what
about monomicrobial and polymicrobial, so staph is one of your polymicrobial in
your intra-abdominal, whatever process, and then your skin and soft tissue is
staph, do you think you can extrapolate?
DR.
BRADLEY: I think it would be difficult
to extrapolate polymicrobial to a single drug simply because in the abdomen and
in deep head and neck space infections where you have got so many different
organisms, the quality of pathogenesis and rapidity of spread seems to be a
function of the multiple organisms rather than the single, and it may be easier
to treat a single organism than once you get them all together, and their
separate pathogenicities add or are synergistic with each other.
DR.
LEGGETT: To face the other issue, what
about an enterococcus in a polymicrobial versus an enterococcus someplace
else? I am not sure I would buy that
either. So, I am not sure we can use
this polymicrobial/monomicrobial in terms of going from one to the other, if
that is what you guys were trying to get at.
DR.
POWERS: I guess what we are asking is
suppose you had some complicated intra-abdominal cases, and some of those were,
say, abscesses that grew pure enterococcus versus you had another drug that
studies the same thing, and then you get enterococcus and a whole bunch of
other stuff.
DR.
LEGGETT: Nope.
DR.
POWERS: But would the pure cases of
enterococcus be more convincing to you?
DR.
LEGGETT: Yes, to me, yes. I will defer to everybody else. Go ahead, Alan.
DR.
CROSS: If you had a pure case of
enterococcal abscess in the belly, I would be impressed. I just recall early on when the coverage for
intra-abdominal sepsis used to be Keflin and kanamycin and, you know,
absolutely no enterococcal coverage.
People have studied it, including Dr. Tally in his earlier days, it just
hasn't been a problem in patients or animal models, so I would be hard pressed.
DR.
LEGGETT: The same applies to
clinda/gent.
DR.
PATTERSON: I guess one comment about
enterococcus is kind of getting back to the pathogen-specific issue. If I knew something worked in enterococcal
bacteremia, then, I would use it for an abscess or skin and soft tissue, and I
think there are times you see significant intra-abdominal infections, for
instance, in liver transplant patients, so I mean I think you do see them
sometimes.
DR.
POWERS: And that is the point. I have seen pure enterococcal abscesses, but
it is in somebody that is throwing bucketloads of antibiotics, you know, in
their third operation after they get it.
DR.
LEGGETT: Right, where it is in their
liver.
DR.
POWERS: Exactly. I think it can exist, it is just unusual.
Mike.
DR.
PROSCHAN: Could the FDA say, you know,
ordinarily you need two well-controlled clinical trials, but if you think you
can make the case based on related bugs, then, you are welcome to try, and then
the advisory committee sees if they made the case.
DR.
POWERS: What we are trying to do here is
outline the criteria that decides whether you make the case. Rather than have
the company come in and just have to de novo make this up, we are trying to
outline this of the things that would allow them to say we meet these criteria
that the advisory committee outlined, which is what we are asking you guys
today, so that they have some template upon which to build their case.
DR.
LEGGETT: I would think it pertinent in
terms of that, in your No. 1, the natural history of the disease, it is not
only the disease, it is natural history of the bug disease complex. As we were saying, that enterococcus melts
away when you don't treat it in the presence of a bunch of other stuff, but VRE
bacteremia, if it's persistent, you know, if somebody is looking for a VRE
thing, they have got a VRE liver abscess, and then a VRE bloodstream, and then
a VRE someplace else, could they lump those together and say yes, I would think
you could make a case for saying yes.
Barth.
DR.
RELLER: That is basically what was done
with quinupristin-dalfopristin.
DR.
LEGGETT: That is an example, going
forward to drug-resistant pneumococcus, or VRSA, or something like that.
DR.
RELLER: To me, the critical issue is the
rigor of the database, and I would add a little caution in trying to get things
too delineated because then if those things are met, you still may be
uncomfortable.
I
think about yesterday's discussion, well, the company did what they were
supposed to do, but, you know, the
lingering discomfort of the solidity of the science, so that I think maybe 95
percent of the way there, but just checking them off shouldn't be--it should be
defensible, not only there, but also rigorous, and I think some of the attempts
here is to raise the bar, or put another way, you get what you ask for, and it
also applies to the agency what is required.
DR.
LEGGETT: Going back to how hard the sort
of persistence question of the pathogen can be applied, not when you are only
trying to do one bug, but when you are trying to do nosocomial-acquired
pneumonia.
Lots
of the times, MRSA in the sputum, I deliberately don't do anything with in the
ICU with somebody who has got an infiltrate.
That data has to be tightened up.
The not normally sterile site, you know, but the data that I am aware
of, and that we have tried, looking at all the sort of protected specimens in
the quantitative, is if anybody has had a whiff of antibiotics, you don't get
anything.
It
is only in France where they don't give antibiotics to anybody before they do
the bronchoscopy that they get anything, and it is only in those one or two
places that could publish those studies, nobody else can replicate that.
DR.
POWERS: So, it sounds like what I am
hearing is there should be an eighth criteria on here, and that has to do with
the quality and rigor of the trial.
DR.
LEGGETT: Definitely.
John.
DR.
BRADLEY: Looking at 7, thinking of
organisms, in most of the studies that I have done, and in what you said
earlier, John, that the FDA looks to treat infections, when there is a clinical
trial, when a patient comes into the hospital, we are looking for infectious
disease diagnoses, and then we look to see if that patient qualifies in terms
of the types of pathogens that we are interested in treating, but what Dr.
Reller is saying, and you seem to have agreed with, particularly with
dalfopristin-quinupristin, is supplementary data that is organism-specific, not
site-specific.
Am I
hearing you say that if there is a particular indication like pneumonia, and a
company would like Pseudomonas as an indication for pneumonia, that you would
accept my screening from the micro lab and taking Pseudomonas infections other
than pneumonia, so bacteremias, endocarditis, prosthetic joint, you know, all
range of things that are not pneumonia--
DR.
LEGGETT: Except UTI.
DR.
BRADLEY: Except UTI, you know, the
quality of data, serious infections that you need the drug, and provide you
with supplemental data for the organism that is organism-driven, not
infection-driven.
DR.
GOLDBERGER: I think that basically we
recognize, and this is something we have sort of touched on a couple times,
that for some of the more difficult-to-study organisms, including some that
despite the fact that they are difficult to study, in no way means that they
are not important. We talked about an
Acinetobacter, there are other examples.
It
is going to be necessary, I think, to be able to pool data across more than one
indication, and I think you can recognize that much of the discussion that we
have had today about how indications support one another is the kind of
discussion that is necessary as part of thinking conceptually how we can take
organisms across the different sites and pool them, but I think it is
inevitable if we are going to be able to draw some kinds of conclusions about
whether a drug works.
You
can argue, on one hand, the goal from the pharmaceutical company is, of course,
to get this in their product labeling, which is fine because they need to have
an incentive in order to do all this work, but realistically, that is hopefully
intimately tied to the idea that we can actually draw some meaningful
conclusions about whether the drug actually performs.
In
order to do that, it is clear it is going to be necessary to do this, so in
addition to a lot of obviously the traditional indications and listing some
organisms, it is clear in certain circumstances we will need to be able to
grant some sort of organism-specific approval that will utilize data across
more than one indication. I think it is
inevitable.
What
we want to do is to do it as well as we can. I think if you think about what
everybody is saying here, what everybody is saying is and almost irrespective
of whether we were having the discussion we are having, is that there are
issues still in how the clinical trials are performed, and they could be done
better.
We
have talked about it for sinusitis, we have talked about it for otitis, we have
talked about it for pneumonia, we have talked about it for almost every--well, and
that is what we are moving toward.
On
the other hand, what we are also hopefully moving towards is providing an
incentive for industry to be interested in doing it better because instead of
doing a lot of trials that are at best so-so, ultimately, the goal is to move
to a fewer number of trials that are better performed with better endpoints,
with better microbiology, and the link to that is this further incentive of how
organisms can sort of be used across more than one indication.
That
is really what we are trying to do.
DR.
LEGGETT: Could I go back to sort of the
real world situation? I don't know if,
say, piperacillin or piperacillin-tazobactam, or some drug, for instance, that
did not get intra-abdominal and went for pneumonia, or got intra-abdominal and
then did not go for a pneumonia trial, but you knew the MIC and the
susceptibility data in real life, do you not use your pip-whatever it is in the
belly after you have used it before in the pneumonia, and vice versa?
So,
how much higher does the hurdle have to be, which is I think what you are
trying to get at, so we should think about the way we actually treat people
with antibiotics when we are discussing this.
DR.
POWERS: Can I sort of follow up on that
for a second, because one of the things I think that came out of the last
meeting we had in February was a misunderstanding of what we were saying when
we were saying accepting pooled information.
That
would still need to be held down by efficacy data in the disease in which that
resistant pathogen is most likely to be found.
So, in other words, suppose you wanted to go for methicillin-resistant
Staph aureus, the two places you would most likely see that would be
complicated skin and, say, hospital-acquired pneumonia.
So,
if you did a hospital-acquired pneumonia trial and only came up with a few
MRSAs, you could then do this other trial, pooling the information, but if you
just come to us with all that pooled information and no hospital-acquired
pneumonia trial, that is not very helpful.
DR.
LEGGETT: Jan.
DR.
PATTERSON: I was just going to say about
extrapolating from the non-pneumonia infections to pneumonia. I think that is where Criteria No. 3 would
come in as pretty high priority about making sure you had tissue levels,
because not all antibiotics get into the lung equally well, so that would
become important.
Then,
just thinking about Pseudomonas pneumonia, I mean even if you had a complicated
skin and skin structure infection due to Pseudomonas, I think Pseudomonas
pneumonia is harder to treat. For instance, you would definitely use
combination therapy for Pseudomonas pneumonia, whereas, with the other one, if
you combined it with surgery, you might not need combination therapy for as
long at least.
So,
I think for that particular pathogen, you would have to be a little bit careful
going from non-pneumonia to pneumonia.
DR.
LEGGETT: To bring No. 2 back into this,
Pseudomonas, would you accept an intra-abdominal abscess that got drained, that
had the resistant Pseudomonas in it, if you had lung data or vice versa?
In
other words, a good study in pneumonia that cleared the resistant Pseudomonas,
and then you had other supportive data, say, an intra-abdominal abscess drained
or had surgery, would that be acceptable?
Trying to get at No. 2.
DR.
PATTERSON: Going from pneumonia to the
abscess, you mean?
DR.
LEGGETT: Yes.
DR.
PATTERSON: Yes, I would accept that.
DR.
LEGGETT: And is it a directionality,
would you not go the other way?
DR.
PATTERSON: Well, that is what I am saying. I don't know that I would necessarily go the
other way for Pseudomonas, I might for some other pathogens, but I would want
to know about the tissue levels if I was going the other way.
DR.
LEGGETT: Back to No. 3, there are some
significant differences in the surface-to-volume ratio in the abdomen than
there is in the lung, so I would be very hesitant going from the belly to the
lung personally.
Keith,
what is your take on what can be done in terms of No. 3, in terms of helping
with resistance trials and in vitro, in vivo, and stuff?
DR.
RODVOLD: Well, in 3, where you are
looking at basically tissue levels or concentrations of fluids, is that again I
think, as you are putting the whole package together, it lends you support in
that disease state.
The
problem in the area is that tissue samples, I have never been hooked to
efficacy to a significant degree, and someone that does research in the area
that I do, I mean that is the common criticism we get, you know, elegantly
designed study, data is really meaningful, but there is no link to showing that
those samples and those levels of concentrations prove that efficacy is going
to occur.
It
gives people a comfortability level, I think that is what it does, and
supports, as you trying to say I have got 10 Pseudomonas and I have
concentrations in the lung that equivalent or higher in the plasma, and it
works in the plasma, it is going to probably work there, as well.
DR.
POWERS: Let me give you an example of
where we encounter something like this.
Norfloxacin is indicated for urinary tract infections. Do you feel real good about using it for
pneumonia, and if not, why not?
DR.
RODVOLD: Well, in that case, it doesn't
have any systemic levels in the blood, in the first place.
DR.
POWERS: That's what we are talking
about. Maybe we didn't phrase this like tissue levels is not the right
word. I guess maybe we should broadly
say gets to the site of infection at all.
DR.
RODVOLD: I think that most people
believe that it needs to be in the site of infection, but if it's there, it
doesn't necessarily still link you to efficacy.
DR.
POWERS: Right, not relative
concentrations, just the fact that it has to get there at all.
DR.
RODVOLD: But, again, I think it's a
supportive tool, and especially for the industry, from the industry perspective
for them, is that you are trying to make them fast-track to get an approval or
get it in their package, it's another thing if they have it, it allows you to
be a little bit more comfortable, but they still need efficacy data in the
indication.
If
you have 10, 15, or however many pathogens, I think most people feel more
comfortable with it. The whole kicker
with that is, though, I can tell you from the number of phone calls I get and
the conversation with people is that the quality of those studies have got to
be done right, as well.
Most
people call me to ask me how we do the studies, and they are not sure what they
are going to do and how they do them, and there is only a few sites around the
area that really know, in a specific tissue, how to do them.
We
do lung, but I don't do a lot of the other ones, so I am very cautious in
jumping over there until we make sure we have the methodology done right. So, the methodology, again, good data is
going to come to you.
DR.
LEGGETT: Barth.
DR.
RELLER: Maybe a comprehensive way of
putting this is the necessary, but not sufficient concept, the necessity of
having adequate concentrations at the site of infection, and this also
extends--well, there are high concentrations in urine, but it is also the
recognized published quantitative relationships that are necessary.
NCSF,
the 10-fold margin of bactericidal activity, that many drugs get into the
urinary tract, but not all drugs get into the urinary tract, and the ones that
don't get in there are not good agents for urinary tract infections, so without
which, you can't expect efficacy and that alone doesn't necessarily constitute
efficacy of adequate concentration, and adequate has some quantitative
concentrative relationships that are recognized in some sites that are more
important than others.
Coming
back to what we haven't discussed a lot is complicated intra-abdominal
infections. The integrity of the
database and what you can rely on microbiologically, I think there is more
recent published data in this area, as well.
For
example, the microbiology that you can rely on in intra-abdominal collections
of pus, drainage or not, are the initial CT-guided aspirates, not what is
draining out of the pigtail catheter on the fourth, fifth, sixth day, but what
is achieved initially. That is one
point.
Secondly,
if one has multiple, which is frequently the case, collections in the abdomen,
that we know that they need to be drained, you know, over a certain size, but I
mean if there are multiple collections, there are multiple sites that need to
be drained, but they also need to be sampled.
There
are also good published data on the lack of complete correlation between one
collection and another collection in terms of the microbiology, so that
clearly, drainage is necessary, but I think with some of these organisms, it is
not sufficient, and what used to be true is not necessarily, as Jan and others
have pointed out, for example, with the enterococcus that may have been
dismissed 20 years ago in a polymicrobial collection, it is not necessarily
dismissed in a post-liver transplant with a collection of pus.
We
know that it is real when it's associated with bacteremia, but it is probably
real even without always demonstrating the bacteremia when it is got by
CT-guided aspirate. So, I think the
techniques for getting the microbiology are better than they used to be, and we
need to look at first tap and each one drained tap information in the microbiology
and the correlation with efficacy of these agents in complicated
intra-abdominal infection.
And
then having those data and what the response is adds support to the potential,
not the automatic, but the potential in the resistant organisms of some extra
utility in considering the efficacy of the compound against a given resistant
pathogen across body sites.
DR.
LEGGETT: In terms of across body sites,
I was looking there. I don't think I
would allow that resistant pathogen in bronchitis or just a sputum without some
illness at all, ever, unless it was part of a trial that was
placebo-controlled.
What
about the situation in which you have a pathogen that is hard to come up with
like drug-resistant pneumococcus, and you use penicillin-susceptible
pneumococcus with great data, bacteremic pneumonias, and then you do your
animal model trial that tells you that you are going to kill it dead from your
PK/PD modeling, how much more data do you think is reasonable before you are
going to use that in real life, in other words, is this a situation where you
would allow 15 bacteremic pneumonias that are treated with this drug when you
had all that supporting data and PK/PD modeling?
DR.
RELLER: Well, I think if you have the
PK/PD data, the animal model, a relatively small number, but those are golden
cases, you know, accompanied by bacteremia, and you have got the NV drode [?],
legitimate, NCCLS methodology data that the, quote, "resistant"
organisms are susceptible to compound X, and the mechanism of resistance, there
are good data in vitro, that there is no cross-resistance whatsoever, the
resistance mechanism isn't totally different, you know, you don't need 100
cases of resistant when you put all of the components together.
I
think Keith was talking about that earlier.
I mean if you have got a beautiful package that passes muster based on
what is known about mechanisms of resistance, doing everything that you have
done first-class, you don't need the numbers.
DR.
LEGGETT: The reason I brought that up
again is because I want to go back to the one dose azithromycin for the ear.
Suppose
we get into a situation where you have got dueling PK/PD stuff, are we going to
hence forward say you are going to have to show us more data, or what happens
if the company comes up with some clinical points or has a few bugs, but the
PK/PD says it shouldn't work or, as Dr. Schentag said earlier, they aim at 25,
and we know we want 100 if we are not going to see resistance in a couple of
months, I think those things need to be
fleshed out in terms of your criteria for allowing resistant pathogens.
You
were going to say something, John?
DR.
BRADLEY: I was just going to support the
statement that you made when there was that long pause that no one was saying
anything and Barth agreed with you, and I think everything Barth said regarding
the package, the complete package, is absolutely correct.
DR.
POWERS: One of the things that we deal
with is when the package doesn't hold together.
I think this brought this up earlier today. What we saw yesterday was some information on
quinolone-resistant organisms in a drug that had zero anti-pneumococcal
quinolone isolates in its clinical development package, and showed an animal
study that showed lack of eradication when the drug was given twice a day
compared to when it was given once a day in an animal model.
So,
what we do we do when that information package doesn't hold together?
DR.
LEGGETT: I personally, if it comes
across again, I am going to be much harder than I was yesterday. That was a
terrible model. It wasn't a model of
infection, it was a preventive, prophylactic model, and you could see the
dropoff right at 0.25, you know, 0.5 was certainly a dropoff, but I didn't want
to go too far down the NCCLS road because you are going to be doing that later,
but that was really very disturbing to me especially with them trying to say
that they were going to get quinolone-resistant--no way in m view.
Alan.
DR.
CROSS: I think we also have to be
careful when we talk about animal models between the PK/PD models versus infection
models. I think certainly in terms of
the latter, it is very difficult to have a uniformly accepted model that
everyone is comfortable with the data that is collected and how it is
interpreted.
I
just have to always harken back to in the area of sepsis where there really
isn't one uniformly accepted animal model, and I would probably hazard that is
probably the same in terms of the--
DR.
LEGGETT: Yes, in that little package,
that was definitely just an animal model, and not a PK/PD model, which to me
what you take from that is the goal that you are going to use in your clinical
studies, not that it works or not, and that you can then sort of use it as a
surrogate endpoint, no.
DR.
BRADLEY: You said that you have got a
PK/PD working group, and I think when a sponsor comes to you with a request for
an indication, you can share with them the animal model that you think would
best fit the types of indications that they are ultimately looking for.
As I
understand it, you know lots of the information that the sponsor is looking for
ultimately when they come to you, and there is much more dialogue upfront
rather than waiting for a sponsor to just come up with data, dump it in your lap, and say, "and here
is the animal model we used," and have that not be the appropriate one
that you feel is the best and most predictive model.
DR.
POWERS: I think in the future, at some
point we will need to have a more detailed discussion about this issue of
pharmacodynamics, but some of the issues of how these studies are done are
important in that realm, as well, as far as when you actually measure it, how
long you wait, et cetera.
Although
we have heard several times from people at this advisory committee, there are
other folks within that field that feel differently about how those studies
should be done, and we need to probably address that at some point in the
future.
DR.
LEGGETT: Ellen.
DR.
WALD: In the practice of clinical
medicine, one of the things that makes interpretation of microbiologic data
difficult, especially in things like intra-abdominal infections, is that the
patient has often received a few doses of antibiotics before the material is
available for culture.
I am
participating in a pneumonia study now, and it really surprised me, but I
presume that you guys okayed this, which allows me to enroll patients 24 hours
after they have received another antibiotic.
Now, I can't do that in good conscience, and so I am not doing it, but I
suspect that other investigators who are entering patients in this trial are.
What
do you learn from that and what should be the posture?
DR.
POWERS: This goes to something Dr.
Goldberger said earlier. In a perfect
world, one would obviously like to enroll pristine patients that didn't get any
antibiotic. It becomes very difficult, though, to enroll people that way
especially--you know, when I was an infectious disease fellow trotting in at 3
o'clock in the morning to enroll those people in those trials.
The
flip side of that, though, is that would you expect one dose of a different
antibiotic to cure the patient, and in the long run, what we want to look at
is, you know, what was the actual effect.
So, if a person gets one dose of ceftriaxone and then gets nine more
days of drug X, is it the ceftriaxone that cured them or not.
This
goes to a bigger issue, though, and that is, you know, when the perfect becomes
the enemy of the good, where if we require people to do trials that way, and
the companies say forget it, it's too hard to do it, and then we get no data.
DR.
WALD: Well, I would say that
ceftriaxones are a pretty powerful drug, and I would really not know the answer
to the question that you posed, is the clinical outcome a consequence at least
in great part from one very powerful drug and some other not so powerful drug.
DR.
LEGGETT: I think people are going to
have to be a little bit more inventive of trying to enroll people's
pathogens. If you use your pneumococcal
urine antigen after you have received one dose of ceftriaxone, and then you use
your drug X for 10 days, I will buy that, but just allowing clinical data
because, quote, "you had this infiltrate," and you enrolled somebody
on ceftriaxone is a much weaker endpoint.
I think that is what Ellen is getting at.
Whether
this would have a lot of bearing on anything except drug-resistant pneumococcus
is unclear in that example, but I mean I could think of other situations.
I
had a question. In the proposed criteria
for resistant pathogens, No. 6, host effects, what sort of things were you guys
thinking about in terms of the criteria?
DR.
COX: I think what we are talking about
here are if we are looking to take data and use that to support another
indication, if there were significant differences in host factors, say, for
instance, one indication was in the study of immunocompromised patients,
patients who were ventilated or other factors, I mean it would certainly seem
reasonable to have some degree of reservation about extrapolating that data
from a more immunosuppressed host to a less immunosuppressed host.
So,
I think that is sort of what we are trying to get at there and trying to
characterize that, and we are looking for comment on that.
DR.
LEGGETT: Do you want to start, Alan?
DR.
CROSS: I am sorry, I am not sure I
followed your comment. Are you saying or
asking is it possible to extrapolate from a more compromised to a less
compromised patient?
DR.
COX: What we are getting at is the host
factors. If you had a more
immunocompromised patient, it would seem reasonable to have some degree of
hesitancy to extrapolate that data to a less immunocompromised host, so we are
looking at this as sort of criteria that would allow us to assess whether one
indication could support another one, and host factors seem to be important.
So,
yes, I mean I guess we are asking the question of in what situations would host
factors give you hesitation to extrapolate data or not extrapolate, but using
supportive data from one indication to support another indication.
DR.
POWERS: If a drug was indicated for
febrile neutropenia, bacterial drug for febrile neutropenia, how good would
that make you feel about hospital-acquired pneumonia in non-immunocompromised
population?
DR.
CROSS: I will give you a different
example. I see lots of patients who are neutropenic, who have VRE, so they have
host defenses that are compromised, there are a bunch of other
immunosuppressive drugs. If I have an
agent that is effective in clearing the VRE in that patient, I would have no
hesitation going in the other direction.
DR.
POWERS: But remember we are talking
about a different indication. We are not
talking about the same indication in neutropenic versus non-neutropenic. We are trying to extrapolate across different
disease states.
That
is why I used the example of two different diseases all together, of empiric
therapy for bacterial infections in neutropenic patients compared to some other
completely different disease, not empiric--well, you don't give empiric therapy
to non-neutropenic patients.
DR.
LEGGETT: How about you grow Pseudomonas
out of the bloodstream when you are neutropenic, and then you have got a normal
host with a complicated skin and soft tissue infection, would that data, if you
cleared that, would you like to hear that at this meeting?
DR.
CROSS: Yes, I would feel pretty
comfortable with that because I know the importance, let's say, of neutrophils
in Pseudomonas infections, and if it worked in the absence of it, I would think
in someone who had it--
DR.
POWERS: How about the other way around,
complicated skin infections with Pseudomonas, and then referring that to the
neutropenic compromised host?
DR.
CROSS: I wouldn't know what the
contribution of the neutrophils is in that situation.
DR.
POWERS: So, there would be a
directionality to this.
DR.
LEGGETT: What about Pseudomonas
bacteremia from presumed GI tract in your neutropenic with no infiltrate to
Pseudomonas pneumonia in a hospitalized patient who is not immunocompromised?
DR.
CROSS: I think as Jan pointed out, at
least historically, Pseudomonas pneumonia with bacteremia is a horse of a
completely different color.
DR.
LEGGETT: I don't think I would feel
comfortable going from a neutropenic bacteremic patient no matter what--unless
it was the pneumonia, the source, to the lung in a non-compromised person.
Barth.
DR.
RELLER: The issue is the enormous
numbers of organisms and what you are asking the antibiotic to do. Maybe there
is one place, not that this comes up very commonly even though it is
occasionally seen, and that is the sort of stringency required for Pseudomonas
meningitis, so if it worked in Pseudomonas meningitis, maybe you could have
some benefit to the lung.
John
asked earlier, and I want to not miss the opportunity to be a little
provocative on this one, you said what do we do when the data don't hang
together in a package. Well, I would
hope you would exercise your regulatory responsibility and consider the
advisory committee exactly what the name says, advisory, and that you would give
no broader indication than what the substantive scientific data allowed until
additional information was forthcoming that would allow expansion of the
indication as regards organism or site of infection.
DR.
LEGGETT: Are you implying a ruling
committee or advisory committee?
DR.
RELLER: What I am saying is that the
agency is privy to the entire package. I
mean there are limitations to what any advisory committee, no matter what its
composition and how hard they work and how carefully they think, can do in the
course of a few hours relative to the detail that the agency is privy to. That is all I am saying.
DR.
LEGGETT: Beyond that, there is all the
information that is not yet done when we are meeting, that comes up later, for
instance, as well as all the stuff that went on before.
One
thing maybe to consider would be another--well, I don't know if you guys can
even do this--but another venue to then get secondary feedback if more
information comes in, but the package still doesn't look good, you know,
without going through the whole process, is there any way of getting a
"second" look or something like that, or what is the rules?
DR.
POWERS: Usually, we can bring it back
here a second time.
DR.
LEGGETT: Are there any of these other
criteria that you want to run through more at length?
DR.
POWERS: I think we can probably sum this
up. It sounds like what we heard was that these seven criteria are pretty good,
they need to be arranged in a certain way, putting the microbiology of the
disease and the similar site up at the top as No. 1 and 2, and then we need to
add an eighth criteria to this, to say that these studies need to be also of
high quality and rigor.
DR.
LEGGETT: That is close. I will tell you the way I did it.
No.
1 is the similarity in spectrum, which you guys have as 7. No. 2 is the rigor of the trial. No. 3 is the similar site, and then it gets
less. No. 4 is the characteristics,
which you guys have as No. 3. Then, No.
5 is the similar--sorry, I am getting lost because I numbered them again--at
some point, No. 5 or 6, or whatever the next number is, is your guys No. 2, the
factors other than the antimicrobial.
The
final two, the next to the last would be the host effects, and the last one is
the monomicrobial versus polymicrobial.
Jan,
you were the original re-arranger of the list.
DR.
PATTERSON: I think I had put No. 5 as
No. 2, but I think the rigor of the trial is very important, so I think that is
very important to have up there.
Summary
DR.
LEGGETT: Any other comments by
anyone? Okay.
I
think basically, this morning we heard about linkage of resistance determinants
in bacteria and we looked at and basically didn't have much to say about a
draft of criteria of listing pathogens of public health importance, so I think
that means they are probably pretty close, and we heard an industry
perspective.
We
spent lots of time discussing the criteria that was presented, but I think we
came up with a little fundamental change and lots of tweaking that may or may
not be useful. I think the FDA's list is
coming close to being finished and the pathogens of priority further analyzed
to get more data.
This
afternoon we heard about being sure to incorporate PK/PD concepts not only into
the new drug approval process, but also in prioritizing the list of pathogens
for targeting drug development, the complexities of relating clinical data from
one disease state to the other, and then some, and how clinicians eventually
try to make sense of the bug-drug host interactions in treating people after
all the above is said and done and behind us.
I
think that you might want to draw upon your own clinical experiences as you
guys start thinking about the clinical trials things, and thinking more the way
we were talking there in real life, if you know the drug works against the bug
in one situation, would you use it in another, and I think let reality sort of
filter into regulation in terms of trying to come up with what you feel
comfortable with.
In
the few minutes we had today, I don't think we spent enough time thinking about
all the permutations of that.
Anybody
else have anything to say?
[No
response.]
DR.
LEGGETT: Thank you all for putting up
with a long day. Tomorrow, we are going
to start at 8:00. Thank you.
[Whereupon,
the committee was adjourned at 4:05 p.m., to reconvene at 8:00 a.m., Thursday,
March 6, 2003.]
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