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

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. Chemical Inducers for In Vitro Experiments* (5/1/2006)

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

1. Except for the cases noted below, the following test substrates were used: CYP1A2, 7-ethoxyresorufin; CYP 2A6, coumarin; CYP2C9, tolbutamide, CYP2C19, S-mephenytoin; CYP3A4, testosterone.
2. CYP1A2: 1 of 4 references for b -naphthoflavone used phenacetin.
3. CYP3A4: 2 of 13 references for rifampin and 1 of 3 references for phenobarbital used midazolam.
4. CYP3A4: 1 of the 4 references for dexamethasone used nifedipine.

In vivo

 Table 4. Examples of in vivo substrate, inhibitor, and inducer for specific CYP enzymes for study (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 CYP3A inhibitors *⁽¹⁾  (5/1/2006)

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

⁽¹⁾ Please note the following:

• A strong inhibitor is one that caused a ≥ 5-fold increase in the plasma AUC values or more than 80% decrease in clearance of CYP3A substrates (not limited to midazolam, a sensitive CYP3A substrate) in clinical evaluations
• A moderate inhibitor is one that caused a ≥ 2- but < 5-fold increase in the AUC values or 50-80% decrease in clearance of sensitive CYP3A substrates when the inhibitor was given at the highest approved dose and the shortest dosing interval in clinical evaluations.
• A weak inhibitor is one that caused a ≥ 1.25 - but < 2-fold increase in the AUC values or 20-50% decrease in clearance of sensitive CYP3A substrates when the inhibitor was given at the highest approved dose and the shortest dosing interval in clinical evaluations

(a) The effect of grapefruit juice varies widely.

Table 6. Classification of inhibitors of other CYP enzymes * ⁽¹⁾ (5/1/2006)

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

⁽¹⁾ Please note the following:

• A strong inhibitor is one that caused a > 5-fold increase in the plasma AUC values or more than 80% decrease in clearance of CYP substrates (not limited to sensitive CYP substrate) in clinical evaluations
• A moderate inhibitor is one that caused a > 2- but < 5-fold increase in the AUC values or 50-80% decrease in clearance of sensitive CYP substrates when the inhibitor was given at the highest approved dose and the shortest dosing interval in clinical evaluations.
• A weak inhibitor is one that caused a > 1.25 - but < 2-fold increase in the AUC values or 20-50% decrease in clearance of sensitive CYP substrates when the inhibitor was given at the highest approved dose and the shortest dosing interval in clinical evaluations

Classification of Substrates

Table 7. Examples ⁽¹⁾ of sensitive CYP3A substrates or CYP3A substrates with narrow therapeutic range * (5/1/2006)

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

1. Sensitive CYP3A substrates refers to drugs whose plasma AUC values have been shown to increase 5-fold or higher when co-administered with a known CYP3A inhibitor.
2. CYP3A substrates with narrow therapeutic range refers to drugs whose exposure-response indicates that increases in their exposure levels by the concomitant use of CYP3A inhibitors may lead to serious safety concerns (e.g., Torsades de Pointes).

(a) Not available in the United States.

Table 8. Examples sensitive CYP substrates or CYP substrates with narrow therapeutic range * (5/1/2006)

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

1. 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.
2. CYP substrates with narrow therapeutic range refers to drugs whose exposure-response indicates that increases in their exposure levels by the concomitant use of CYP inhibitors may lead to serious safety concerns (e.g., Torsades de Pointes).

P-gp Transporters

 Table 9. 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 10. 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 11. 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.

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Date created: May 1, 2006
Date updated: October 11, 2006

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