Why is CDC launching trials of pre-exposure prophylaxis for HIV prevention?
CDC is sponsoring these trials because safe and effective new
approaches to HIV prevention are urgently needed. More than 7,000
people continue to become infected around the world every day
(approximately 2.7 million per year). Although behavior change
programs have contributed to dramatic reductions in the number of
annual infections in the United States and many other nations, far
too many people remain at high risk.
With an effective vaccine years away, there is mounting evidence that
antiretroviral agents may be able to play an important role in reducing the
risk for transmission. Researchers believe that an HIV drug approved by the
U.S. Food and Drug Administration (FDA)―tenofovir disoproxil fumarate (tenofovir,
brand name Viread) used alone or in combination with emtricitabine
(together, known by the brand name Truvada)―taken daily as an oral
preventive drug, is among the most important new prevention approaches being
investigated today. The approach is called pre-exposure prophylaxis, or PrEP.
If proven safe and effective, PrEP could help address the urgent need for
a female-controlled prevention method for women worldwide who are unable,
because of cultural and other barriers, to negotiate condom use.
Furthermore, if effective, it could provide an additional safety net for all
men and women at risk due to sexual or drug-using behaviors, when combined
with reducing the number of sexual partners, HIV counseling and testing,
condom use, use of sterile syringes, and other prevention measures.
Back to Questions
How would HIV treatment drugs work to protect against HIV infection?
The concept of providing a preventive drug before exposure to an
infectious agent is not new. For example, travelers to an area where
malaria is common are advised to take medication before and during
travel to prevent the disease. The medicine to prevent illness is
then already in their bloodstream if they are exposed to the malaria
parasite.
Researchers believe that the same concept may work to protect people from
HIV infection. Theoretically, if HIV replication can be inhibited from the
moment the virus enters the body, it may not be able to establish a
permanent infection.
Back to Questions
What data suggest that this approach may be safe and effective?
Several sources of data suggest that an antiretroviral drug, taken
regularly, may prove effective in reducing a person’s risk for HIV
infection:
- Providing a single dose of the antiretroviral drug nevirapine to
HIV-infected women during labor and to their newborns immediately after
birth has reduced the risk for mother-to-child transmission of HIV by
about 50 percent.
- In observational studies, the antiretroviral drug zidovudine, taken
soon after exposure and continued for several weeks, has been associated
with an 80 percent reduction in the risk of HIV infection among health
care workers after needlesticks or other accidental exposures.
- Animal studies have shown that tenofovir, administered before and
immediately after a single retroviral exposure, can reduce the
transmission of a virus similar to HIV in monkeys.
- Finally, animal studies have also demonstrated that pre-exposure
administration of tenofovir plus emtricitabine, provided significant
protection to monkeys exposed repeatedly to an HIV-like virus.
The safety and efficacy of tenofovir and a tenofovir-emtricitabine
combination pill for the treatment of HIV infection has been well
established in clinical studies and medical settings. The FDA licensed
tenofovir for use as an HIV treatment in adults in October 2001, and
licensed the tenofovir-emtricitabine combination pill for use as an HIV
treatment in August 2004. More than 200,000 HIV-infected patients around the
world have now used these drugs. Among these patients, tenofovir has
resulted in a relatively low level of side effects, compared to other HIV
treatments. The most common side effects include nausea and vomiting, and
loss of appetite. Tenofovir plus emtricitabine has also been associated with
a relatively low level of side effects, which include diarrhea, nausea,
fatigue, headache, dizziness, and rash.
One of the key objectives of these trials is to determine for certain
whether the study drugs are safe and well tolerated by HIV-negative persons;
and safety will be closely monitored throughout the trials. Researchers
expect side effects to be even less common in the healthy, HIV-negative
volunteers in these HIV prevention trials.
Why study two different drugs?
Globally, almost 7,000 new HIV infections occur daily, and additional
prevention approaches are urgently needed. A combination of studies – of
both tenofovir alone and tenofovir plus emtricitabine – will allow us to
move forward as quickly and effectively as possible in the search for new
solutions.
There are significant data suggesting the promise of both of these HIV
treatment drugs. Because we don’t yet know for sure how the animal data will
correlate to human protection, we believe it is essential to move forward as
quickly as possible to evaluate both of these promising interventions.
Back to Questions
|