26 DRUG METABOLISM
Table 5.1:CYP450 isoenzymes most commonly involved in drug metabolism with representative drug substrates and their
specific inhibitors and inducersEnzyme Substrate Inhibitor Inducer
CYP1A2 Caffeine Amiodarone Insulin
Clozapine Cimetidine Cruciferous vegetables
Theophylline Fluoroquinolones Nafcillin
Warfarin (R) Fluvoxamine Omeprazole
CYP2C9a Celecoxib
Losartan Amiodarone Barbiturates
NSAIDs Fluconazole Rifampicin
Sulphonylureas Fluoxetine/Fluvoxamine
Phenytoin Lansoprazole
Warfarin (S) Sulfamethoxazole
Ticlopidine
CYP2C19a Diazepam Fluoxetine Carbamazepine
Moclobamide Ketoconazole Prednisone
Omeprazole Rifampicin
Pantoprazole
Proguanil
CYP2D6a Codeine (opioids) Amiodarone Dexamethasone
Dextromethorphan Celecoxib Rifampicin
Haloperidol Cimetidine
Metoprolol Ecstasy (MDMA)
Nortriptyline Fluoxetine
Pravastatin Quinidine
Propafenone
CYP2E1 Chlormezanone Diethyldithio-carbamate Ethanol
Paracetamol Isoniazid
Theophylline
CYP3A4 Alprazolam Amiodarone Barbiturates
Atorvastatin Diltiazem Carbamazepine
Ciclosporin Erythromycin (and other Efavirenz
macrolides) Glucocorticosteroids
(and other steroids)
Hydrocortisone Gestodene Nevirapine
Lidocaine Grapefruit juice Phenytoin
Lovastatin Fluvoxamine Pioglitazone
Fluconazole/Itraconazole St John’s wort
Midazolam Ketoconazole
Nifedipine (many CCBs) Nefazodone
Tamoxifen Nelfinavir/Ritonavir
Tacrolimus Verapamil
Vincristine Voriconazole
aKnown genetic polymorphisms (Chapter 14).
Approximate percentage of clinically used drugs metabolized by each CYP isoenzyme: CYP3A4, 50%; CYP2D6, 20%; CYP2C,
20%; CYP1A2, 2%; CYP2E1, 2%; other CYPs, 6%.