^a Recommend the use of two structurally unrelated CYP3A4/5 substrates to evaluate in vitro CYP3A4/5 inhibition.

Abbreviations:
CYP: cytochrome P450

Note: Many of these chemical inhibitors are not specific for an individual CYP enzyme. The selectivity and potency of inhibitors should be verified using the same experimental conditions with probe substrates for each CYP enzyme.

^a Time-dependent inhibitors.

Abbreviations:
CYP: cytochrome P450

Abbreviations:
CYP: cytochrome P450.

Note: Index substrates predictably exhibit exposure increases due to inhibition of a given metabolic pathway and are commonly used in prospective clinical DDI studies. See section IV.A.2 of the FDA guidance for industry entitled Clinical Drug Interaction Studies —Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions (January 2020) for details. Sensitive index substrates are index drugs that demonstrate an increase in AUC of ≥5-fold with strong index inhibitors of a given metabolic pathway in clinical DDI studies. Moderately sensitive substrates are drugs that demonstrate an increase in AUC of ≥2- to <5-fold with strong index inhibitors of a given metabolic pathway in clinical DDI studies.

This table provides examples of clinical sensitive or moderately sensitive index substrates and is not intended to be an exhaustive list. Index substrates listed in this table were selected considering their sensitivity, specificity, safety profiles, and adequate number of reported clinical DDI studies with different in vivo inhibitors (≥ 3 for CYP3A or ≥ 2 for CYP1A2, 2C8, 2C9, 2C19, and 2D6). DDI data were collected based on a search of the University of Washington Metabolism and Transport Drug Interaction Database [Hachad et al. (2010), Hum Genomics, 5(1):61], and the list of references is available here.

^a We currently do not have sensitive index substrates for CYP2B6.
^b Also OATP1B1 substrate.
^c Moderately sensitive substrates.
^d S-lansoprazole is a sensitive substrate in CYP2C19 EM subjects.

Abbreviations:
AUC: area under the concentration-time curve; CYP: cytochrome P450; DDI: drug-drug interaction; EM: extensive metabolizer; OATP1B1: organic anion transporting polypeptide 1B1.

Note: Index inhibitors predictably inhibit metabolism via a given pathway and are commonly used in prospective clinical DDI studies. See section IV.A.2 of the FDA guidance for industry entitled Clinical Drug Interaction Studies —Cytochrome P450 Enzyme- and Transporter-Mediated Drug Interactions (January 2020) for details. Strong and moderate inhibitors are drugs that increase the AUC of sensitive index substrates of a given metabolic pathway ≥5-fold and ≥2- to <5-fold, respectively.

This table provides examples of clinical index inhibitors and is not intended to be an exhaustive list. Index inhibitors listed in this table were selected based on potency and selectivity of inhibition, safety profiles, and an adequate number of reported clinical DDI studies with different in vivo substrates [≥ 3 for CYP3A, ≥ 2 for CYP1A2, 2C9, 2C19, and 2D6, or ≥ 1 for CYP2C8 (strong inhibitors)]. DDI data were collected based on a search of the University of Washington Metabolism and Transport Drug Interaction Database [Hachad et al. (2010), Hum Genomics, 5(1):61)], and the list of references is available here.

^a Strong inhibitor of CYP1A2 and CYP2C19, moderate inhibitor of CYP3A, and weak inhibitor of CYP2D6.

^b We currently do not have index inhibitors for CYP2B6.

^c Strong inhibitor of CYP2C8 and inhibitor of OATP1B1 and OAT3.

^d Moderate inhibitor of CYP2C8 at the 75 mg dose of clopidogrel and a weak inhibitor of CYP2B6.

^e Strong inhibitor of CYP2C19 and moderate inhibitor of CYP2C9 and CYP3A.

^f Strong inhibitor of CYP2C19 and CYP2D6.

^g Inhibitor of P-gp (defined as those increasing the AUC of digoxin to ≥1.25-fold).

Abbreviations:
AUC: area under the concentration-time curve; CYP: cytochrome P450; DDI: drug-drug interaction; OATP1B1: organic anion transporting polypeptide 1B1; OAT3: organic anion transporter 3; P-gp: P-glycoprotein.

Note: Strong, moderate, and weak inhibitors are drugs that increase the AUC of sensitive index substrates of a given metabolic pathway ≥5-fold, ≥2 to <5-fold, and ≥1.25 to <2-fold, respectively.

This table provides examples of clinical inhibitors and is not intended to be an exhaustive list. DDI data were collected based on a search of the University of Washington Metabolism and Transport Drug Interaction Database [Hachad et al. (2010), Hum Genomics, 5(1):61].

^a Strong inhibitor of CYP1A2 and CYP2C19, moderate inhibitor of CYP3A, and weak inhibitor of CYP2D6.
^b Moderate inhibitor of CYP2C8 and a weak inhibitor of CYP2B6.
^c Strong inhibitor of CYP2C19 and a weak inhibitor of CYP2B6. The classification as a CYP2B6 inhibitor is based on the AUC change of bupropion. The effect of ticlopidine on hydroxybupropion, which is primarily metabolized by CYP2B6, is larger.
^d Strong inhibitor of CYP3A, moderate inhibitor of CYP2C19, and weak inhibitor of CYP2B6 and CYP2C9.
^e Strong inhibitor of CYP2C8 and an inhibitor of OATP1B1 and OAT3.
^f Strong inhibitor of CYP2C19 and a moderate inhibitor of CYP2C9 and CYP3A.
^g Strong inhibitors of CYP2C19 and CYP2D6.
^h Inhibitor of P-gp (, defined as those increasing AUC or Cmax of digoxin, dabigatran, or edoxaban ≥1.5-fold).
ⁱ Strong inhibitor of CYP3A4 and weak inducer of CYP2B6, CYP2C9, and CYP2C19.
^j Ritonavir is usually given in combination with other anti-HIV or anti-HCV drugs in clinical practice. Caution should be used when extrapolating the observed effect of ritonavir alone to the effect of combination regimens on CYP3A activities.
^k 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 is used (e.g., high dose, double strength) or as a ‘moderate CYP3A inhibitor’ when another preparation is used (e.g., low dose, single strength).
^l The classification is based on studies conducted with intravenously administered conivaptan.
^m Diltiazem increased the AUC of certain sensitive CYP3A substrates (e.g., buspirone) more than 5-fold.

Abbreviations:
AUC: area under the concentration-time curve; CYP: cytochrome P450; DDI: drug-drug interaction; HIV: human immunodeficiency virus; HCV: hepatitis C virus; OATP1B1: organic anion transporting polypeptide 1B1; OAT3: organic anion transporter 3; P-gp: P-glycoprotein.

Note: Strong, moderate, and weak inducers are drugs that decreases the AUC of sensitive index substrates of a given metabolic pathway by ≥80%, ≥50% to <80%, and ≥20% to <50%, respectively.

This table provides examples of clinical index inducers and is not intended to be an exhaustive list. DDI data were collected based on a search of the University of Washington Metabolism and Transport Drug Interaction Database [Hachad et al. (2010), Hum Genomics, 5(1):61].

^a Strong inducer of CYP3A and a moderate inducer of CYP1A2 and CYP2C19.
^b Strong inducer of CYP2C19 and CYP3A and a moderate inducer of CYP1A2, CYP2B6, CYP2C8, and CYP2C9.
^c Strong inducer of CYP2B6 and CYP3A and weak inducer of CYP2C9.
^d Moderate inducer of CYP2B6, CYP2C19, and CYP3A.
^e Weak inducer of CYP2B6, CYP2C9, and CYP2C19. Classification is based on studies conducted with ritonavir itself (not with other anti-HIV drugs) at doses of 100-200 mg/day, although larger effects have been reported in literature for high doses of ritonavir.
^f Moderate inducer of CYP1A2 with a dose of 800 mg/day ritonavir (not with other anti-HIV drugs). The effect on CYP1A2 at lower doses of ritonavir is unknown.
^g Strong inducer of CYP3A and moderate inducer of CYP2C9 and CYP2C19.
^h Strong inducer of CYP3A, moderate inducer of CYP2C19, and weak inducer of CYP2C9.
ⁱ The effect was based on prediction using physiologically based pharmacokinetic (PBPK) modeling.
^j The effect of St. John’s wort varies widely and is preparation dependent.
^k The classification is based on a 200 mg daily dose of cenobamate. Its effect potentially could be stronger at 400 mg/day.
^l The classification is based on effect of 200 mg/day modafinil. A higher dose (400 mg/day) modafinil had a larger induction effect on CYP3A.

Abbreviations:
AUC: area under the concentration-time curve; CYP: cytochrome P450; DDI: drug-drug interaction.

Note: This table provides examples of in vitro substrates for various transporters and is not intended to be an exhaustive list.

Note: The IC50 values of several OATP1B inhibitors measured using estrone-3-sulfate as a substrate were larger than those measured using estradiol-17-beta-glucuronide or pitavastatin as substrates. Thus, using estrone-3-sulfate as a substrate may underpredict the potential of a drug as an inhibitor of OATP1B.

Note: The IC50 values of several OCT2 inhibitors measured using 1-methyl-4-phenylpyridinium (MPP+) as a substrate were larger than those measured using metformin or creatinine as substrate. Thus, using MPP+ as a substrate may underpredict the potential of a drug as an inhibitor of OCT2.
^a Also a substrate of OATPs.
^b Also a substrate of OAT3.
^c Also a substrate of MRP2.
^d Also a substrate of MATEs.
^e Also a substrate of P-gp.
^f Also a substrate of NTCP.
^g Selective substrate of OATP1B3 (vs. OATP1B1).
^h Used in vesicle experiments.
ⁱ Also a substrate of BCRP.
^j Substrate of OCTs and MATEs.

Abbreviations:
BCRP: breast cancer resistance protein; MATE: multidrug and toxin extrusion protein; MRP2: multidrug resistance-associated protein 2; NTCP: Na+-taurocholate co-transporting polypeptide; OAT: organic anion transporter; OATP: organic anion transporting polypeptide; OCT: organic cation transporter; P-gp: P-glycoprotein, also called as multidrug resistance protein 1 (MDR1).

Note: This table provides examples of in vitro inhibitors for various transporters and is not intended to be an exhaustive list.
^a Also an inhibitor of BCRP.
^b Also an inhibitor of NTCP.
^c Also an inhibitor of OATPs.
^d Also an inhibitor of MRP2.
^e Also an inhibitor of OAT3.
^f Also an inhibitor of OCT2.
^g Also an inhibitor of MATEs.
^h Also an inhibitor of P-gp.
ⁱ Preincubation with inhibitors prior to inhibition studies causes a decrease of the Ki value.
^j Selectively inhibit OAT3 at lower concentrations. Note at the concentration inhibiting OAT3, benzylpenicillin also inhibits OATP1B3.

Abbreviations:
BCRP: breast cancer resistance protein; MATE: multidrug and toxin extrusion protein; MRP2: multidrug resistance-associated protein 2; NTCP: Na+-taurocholate co-transporting polypeptide; OAT: organic anion transporter; OATP: organic anion transporting polypeptide; OCT: organic cation transporter; P-gp: P-glycoprotein, also called as multidrug resistance protein 1 (MDR1).

Note: A clinical substrate should meet the following criteria:

• P-gp: (1) AUC fold-increase is ≥1.5 with itraconazole, quinidine, or verapamil co-administration; (2) not extensively metabolized in humans; and (3) in vitro transported by P-gp expression systems.
• BCRP: (1) AUC fold-increase is ≥1.5 with pharmacogenetic alteration of ABCG2 (421C>A) and (2) in vitro transported by BCRP expression systems.
• OATP1B1/OATP1B3: (1) AUC fold-increase is ≥2 with rifampin (single dose) or cyclosporine A co-administration or pharmacogenetic alteration of SLCO1B1 (521T>C); and (2) in vitro transported by OATP1B1 and/or OATP1B3 expression systems.
• OAT1/OAT3: (1) AUC fold-increase is ≥1.5 with probenecid co-administration; (2) fraction excreted unchanged into urine as an unchanged drug is ≥0.5; and (3) in vitro transported by OAT1 and/or OAT3 expression systems.
• OCT2/MATE: (1) AUC fold-increase is ≥1.5 with dolutegravir or pyrimethamine co-administration; (2) fraction excreted unchanged into urine as an unchanged drug is ≥0.5; and (3) in vitro transported by OCT2 and/or MATEs expression systems.

This table provides examples of clinical substrates for various transporters and is not intended to be an exhaustive list. DDI data were collected based on a search of the University of Washington Metabolism and Transport Drug Interaction Database [Hachad et al. (2010), Hum Genomics, 5(1):61].

^a Only affected by intestinal P-gp. Dabigatran etexilate is a pro-drug and converted by carboxylesterase (CES) to dabigatran which is the measured moiety (dabigatran is not a substrate of P-gp). Thus, for correct interpretation of clinical DDI results, pre-assessment of the inhibitory effects of an investigational drug on CES activity should be considered.

^b Also a substrate of OATPs.
^c Also a substrate of OAT3.
^d Also a substrate of MRP2. .
^e Only affected by intestinal BCRP.
^f Also a substrate of BCRP.
^g Also a substrate of P-gp.
^h Also a substrate of CYP3A.
ⁱ In vitro data suggest a higher contribution of OATP1B3 than OATP1B1.
^j Also a substrate of CYP2C9.
^k Also a substrate of CYP2C8.
^l In vitro data suggest a higher contribution of OAT1 than OAT3.
^m These drugs are active moieties of their corresponding pro-drugs, adefovir dipivoxil, oseltamivir, tenofovir alafenamide fumarate (TAF), and tenofovir disoproxil fumarate (TDF). Those pro-drugs are substrates of P-gp.
ⁿ In vitro data suggest a higher contribution of OAT3 than OAT1.

Abbreviations:
AUC: area under the plasma concentration-time curve. BCRP: breast cancer resistance protein; MATE: multidrug and toxin extrusion protein; MRP2: multidrug resistance-associated protein 2; OAT: organic anion transporter; OATP: organic anion transporting polypeptide; OCT: organic cation transporter; P-gp: P-glycoprotein, also called as multidrug resistance protein 1 (MDR1).

Note: Criteria for selecting in vivo inhibitors are as follows:

• P-gp: (1) AUC fold-increase of dabigatran, digoxin, or edoxaban is ≥1.5 with co-administration; and (2) in vitro inhibitor of P-gp.
• BCRP: (1) AUC fold-increase of rosuvastatin or sulfasalazine is ≥1.5 with co-administration and (2) in vitro inhibitor of BCRP.
• OATP1B1/OATP1B3: (1) AUC fold-increase is ≥2 for at least one of clinical substrates in Table 5-1 with co-administration; and (2) in vitro inhibitor of OATPB1 and/or OATP1B3.
• OAT1/OAT3: (1) AUC fold-increase ≥1.5 for at least one of clinical substrates in Table 5-1 with co-administration and (2) in vitro inhibitor of OAT1 and/or OAT3.
• OCT2/MATE: (1) AUC fold-increase of metformin is ≥ 1.5 with co-administration: and (2) in vitro inhibitor of OCT2 and/or MATEs.

This table provides examples of clinical inhibitors for various transporters and is not intended to be an exhaustive list. DDI data were collected based on a search of the University of Washington Metabolism and Transport Drug Interaction Database [Hachad et al. (2010), Hum Genomics, 5(1):61].

^a A number of P-gp inhibitors also inhibit CYP3A.
^b Also an inhibitor of OATP1B1 and/or OATP1B3.
^c Also an inhibitor of BCRP.
^d Also an inhibitor of P-gp.
^e Also an inhibitor of OAT3.
^f Intravenously administered rolapitant does not inhibit BCRP.

Abbreviations:
AUC: area under the plasma concentration-time curve. BCRP: breast cancer resistance protein; MATE: multidrug and toxin extrusion protein; OAT: organic anion transporter; OATP: organic anion transporting polypeptide; OCT: organic cation transporter; P-gp: P-glycoprotein, also called as multidrug resistance protein 1 (MDR1).