Drug Development and Drug Interactions: Table of Substrates, Inhibitors and Inducers

• CYP Enzymes
• In vitro
• In vivo
• Examples of in Vivo Substrate, Inhibitor, and Inducer for Specific CYP Enzymes for Study (oral administration)
• Classification of Inhibitors
• Classification of Substrates

• P-gp Transporters
• Major Human Transporters
• Selected Transporter-Mediated Clinical Significant Drug-Drug Interactions
• Examples of In Vivo Inhibitors and Inducers of Selected Transporters
• Examples of In Vivo Substrates for Selected Transporters Examples of In Vivo
• CYP3A and P-gp Inhibitors and Their Relative Potency

 CYP Enzymes

 In vitro

Table 1: Chemical inhibitors for in vitro experiments* (9/25/2006)

* Note that this is not an exhaustive list which was created May 1, 2006.

1. Substrates used for inhibition studies include: CYP1A2, phenacetin-o-deethylation, theophylline-N-demethylation; CYP2A6, coumarin-7-hydroxylation; CYP2B6, 7-pentoxyresorufin-O-depentylation, bupropion hydroxylation, 7-ethoxy-4-(trifluoromethyl)-coumarin O-deethylation, S-mephenytoin-N-demethylation; Bupropion-hydroxylation; CYP2C8, taxol 6-alpha-hydroxylation; CYP2C9, tolbutamide 4-methylhydroxylation, S-warfarin-7-hydroxylation, phenytoin 4-hydroxylation; 2CYP2C19, (S)-mephenytoin 4-hydroxylation CYP2D6, dextramethorphan O-demethylation, desbrisoquine hyddroxylase; CYP2E1, chlorzoxazone 6-hydroxylation, aniline 4-hydroxylase; CYP3A4/5, testosterone-6ß-hydroxylation, midazolam-1-hydroxylation; cyclosporine hydroxylase; nefedipine dehydrogenation.
2. Furafylline and methoxsalen are mechanism-based inhibitors and should be pre-incubated before adding substrate.
3. cDNA expressing microsomes from human lymphoblast cells.
4. Supersomes, microsomal isolated from insect cells transfected with baculovirus containing CYP2B6.
5. IC50 values.
6. Specific time-dependent inhibitor.

Table 2. Preferred and acceptable chemical substrates for in vitro experiments* (9/25/2006)

* Note that this is not an exhaustive list (created May 1, 2006).

** Recommend use of 2 structurally unrelated CYP3A4/5 substrates for evaluation of in vitro CYP3A inhibition. If the drug inhibits at least one CYP3A substrate in vitro, then in vivo evaluation is warranted.

Table 3. In Vitro CYP Inducers (7/28/2011)

*Note that this is not an exhaustive list.  For an updated list, see the following link
http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm080499.htm.

 In vivo

  Table 4. Examples of in vivo substrate, inhibitor, and inducer of specific CYP enzymes for evaluation (oral administration) ⁽¹⁾ * (5/1/2006)

* Note that this is not an exhaustive list (created May 1, 2006).

1. Substrates for any particular CYP enzyme listed in this table are those with plasma AUC values increased by 2-fold or higher when co-administered with inhibitors of that CYP enzyme; for CYP3A, only those with plasma AUC increased by 5-fold or higher are listed. Inhibitors listed are those that increase plasma AUC values of substrates for that CYP enzyme by 2-fold or higher. For CYP3A inhibitors, only those that increase AUC of CYP3A substrates by 5-fold or higher are listed. Inducers listed are those that decrease plasma AUC values of substrates for that CYP enzyme by 30% or higher.
2. A clinical study can be conducted in smokers as compared to non-smokers (in lieu of an interaction study with an inducer), when appropriate.
3. A clinical study can be conducted in poor metabolizers (PM) as compared to extensive metabolizers (EM) for the specific CYP enzyme (in lieu of an interaction study with an inhibitor), when appropriate.

 Classification of Inhibitors

Table 5.  Classification of In Vivo Inhibitors of CYP Enzymes(1) (7/28/2011)http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm080499.htm.

1. Please note the following:  This is not an exhaustive list.  For an updated list, see the following link
2. A strong inhibitor for a specific CYP is defined as an inhibitor that increases the AUC of a substrate for that CYP by equal or more than 5-fold.
3. A moderate inhibitor for a specific CYP is defined as an inhibitor that increases the AUC of a sensitive substrate for that CYP by less than 5-fold but equal to or more than 2-fold.
4. A weak inhibitor for a specific CYP is defined as an inhibitor that increases the AUC of a sensitive substrate for that CYP by less than 2-fold but equal to or more than 5-fold.
5. Herbal product.
6. Gemfibrozil also inhibits OATP1B1.
7. Fluconazole is listed as a strong CYP2C19 inhibitor based on the AUC ratio of omeprazole, which is also metabolized by CYP3A; fluconazole is a moderate CYP3A inhibitor.
8. Fluvoxamine strongly inhibits CYP1A2 and CYP2C19, but also inhibits CYP2C8/2C9 and CYP3A;
9. Ticlopidine strongly inhibits CYP2C19, but also inhibits CYP3A, CYP2B6, and CYP1A2.
10. Effect seems to be due to CYP2C19 inhibition by ethinyl estradiol.
11. The effect of grapefruit juice varies widely among brands and is concentration-, dose-, and preparation-dependent.  Studies have shown that it can be classified as a “strong CYP3A inhibitor” when a certain preparation was used (e.g., high dose, double strength) or as a “moderate CYP3A inhibitor” when another preparation was used (e.g., low dose, single strength).
12. Withdrawn from the United States market because of safety reasons.

Table 6.  Classification of In Vivo Inducers of CYP Enzymes(1) (7/28/2011)

(1) Please note the following:  This is not an exhaustive list.  For an updated list, see the following link: http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm080499.htm.
(2) For a drug that is a substrate of CYP1A2, the evaluation of the effect of induction of CYP1A2 can be carried out by comparative PK studies in smokers vs. non-smokers. 
(3) The effect of St. John’s wort varies widely and is preparation-dependent.
(4) Herbal product.
(5) Not a marketed drug.

 Classification of Substrates

Table 7. Examples(1) of Sensitive In Vivo CYP Substrates and CYP Substrates with Narrow Therapeutic Range (7/28/2011)

(1)  Note that this is not an exhaustive list.  For an updated list, see the following link: http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm080499.htm.
(2) Sensitive CYP substrates refers to drugs whose plasma AUC values have been shown to increase 5-fold or higher when co-administered with a known CYP inhibitor.
(3)  CYP substrates with narrow therapeutic range refers to drugs whose exposure-response relationship indicates that small increases in their exposure levels by the concomitant use of CYP inhibitors may lead to serious safety concerns (e.g., Torsades de Pointes).
(4) The AUC of these substrates were not increased by 5-fold or more with a CYP2B6 inhibitor, but they represent the most sensitive substrates studied with available inhibitors evaluated to date.
(5) Repaglinide is also a substrate for OATP1B1, and it is only suitable as a CYP2C8 substrate if the inhibition of OATP1B1 by the investigational drug has been ruled out. 
(6) Because a number of CYP3A substrates (e.g., darunavir, maraviroc) are also substrates of P-gp, the observed increase in exposure could be due to inhibition of both CYP3A and P-gp.
(7) Withdrawn from the United States market because of safety reasons.
 

 P-gp Transporters

 Table 8. Acceptable In Vitro P-gp Substrates * (5/1/2006)

* Note that this is not an exhaustive list (created May 1, 2006).

** P _{app, B-A} / P _{app, A-B}; P _app = apparent permeability

*** Data for MDR1-MDCK and MDR1-LLCPK are the ratio observed in transfected cells relative to the ratio observed in respective wild-type cells.

^a Vinblastine is also a substrate for MRP2 that is constitutively expressed in Caco-2, and wild type MDCK and LL-CPK1 cells.

^b Data are derived from net B to A flux in the absence of GF120918, a potent P-gp inhibitor, relative to that observed in the presence of GF120918.

Table 9. In Vitro P-gp Inhibitors * (5/1/2006)

* Note that this is not an exhaustive list (created May 1, 2006).

* Digoxin as a P-gp substrate

** Vinblastine as a P-gp substrate

^a also CYP3A inhibitor

^b also CYP2D6 inhibitor

 Major Human Transporters

Table 10. Major human transporters * ⁽¹⁾ (5/1/2006)

* Note that this is not an exhaustive list (created May 1, 2006).

1. ABC:ATP-binding cassette transporter superfamily; SLC: solute-linked carrier transporter family; SLCO: solute-linked carrier organic anion transporter family; MDR1: multi-drug resistance; MRP: multi-drug resistance related protein; BSEP:bile salt export pump; BCRP: breast cancer resistance protein; OAT: organic anion transporter; OCT: organic cation transporter; NTCP: sodium taurocholate co-transporting polypeptide; ASBT: apical sodium-dependent bile salt transporter.

Table 11.  Selected Transporter^a-Mediated Clinical Significant Drug-Drug Interactions (7/28/2011)

a Abbreviations:  BCRP, breast cancer resistance protein; P-gp, p-glycoprotein; MDR, multidrug resistance:  LST, liver-specific transporters; OATP, organic anion transporting polypeptide; OCT, organic cation transporter; OAT, organic anion transporter
b Implicated transporter refers to the likely transporter; however, because the studies are in vivo, it is not possible to assign definitively specific transporters to these interactions. 
c Minimum predose plasma level (Ctrough) data from Day 4 (48-fold), Day 10 (5-fold) after co-administration.
d Interaction could be partly mediated by OATP1B1.
e Interaction could be partly mediated by BCRP.
f Interaction could be partly mediated by MATE-1/MATE-2K.
g Interaction could be partly mediated by OAT1.

Table 12. Examples of In Vivo Inhibitors and Inducers of Selected Transporters(1) (7/28/2011)

• Please note this is not an exhaustive list.  For an updated list, see the following link http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm080499.htm.
• Inhibitors listed for P-gp are those that showed >25% increase in digoxin AUC or otherwise indicated if substrate is other than digoxin.
• Inducers listed for P-gp are those that showed >20% decrease in digoxin AUC or otherwise indicated if substrate is other than digoxin.
• Inhibitors listed are those that showed >25% increase in fexofenadine AUC.
• Inhibitors listed are those that showed >25% increase in talinolol AUC.
• Not a marketed drug.
• Inducers listed are those that showed >20% decrease in fexofenadine AUC.
• Herbal product.
• Given as a single dose.
• In vitro inhibitors for OATP.  Separation of the in vivo inhibition effect from ritonavir is difficult because this drug is usually co-administered with ritonavir.
• The in vivo inhibition effect of ritonavir cannot be easily estimated because it is usually co-administered with other HIV protease inhibitors that are inhibitors for OATP as well.

Table 13.  Examples of In Vivo Substrates for Selected Transporters(1) (7/28/2011)

• Please note this is not an exhaustive list.  For an updated list, see the following link http://www.fda.gov/Drugs/DevelopmentApprovalProcess/DevelopmentResources/DrugInteractionsLabeling/ucm080499.htm.

 (2)  Selective for OATP1B3.

Table 14. Examples of In Vivo CYP3A and P-gp Inhibitors and Their Relative Potency (7/28/2011)

            *  Data derived with fexofenadine; all other data were derived with digoxin.

Notes:
(1) The University of Washington Drug Interaction Database was used to search the data that defined the in vivo potency of various inhibitors for CYP3A (midazolam was searched as a substrate) and P-gp (digoxin or fexofenadine was searched as a substrate).
(3) Strong, moderate, or weak CYP3A inhibitors are defined as those drugs that increase the AUC of oral midazolam or other CYP3A substrates ≥5-fold, 2-5-fold, and 1.25-2-fold, respectively.