Enzyme induction occurs when chemicals increase the synthesis and activity of an enzyme. This leads to increased metabolism of drugs catalyzed by that enzyme.
When one drug induces the CYP enzyme involved in the biotransformation of another drug, it increases the rate of metabolism of that drug, resulting in a reduced efficacy. The parent drug is metabolized acceleratedly, leading to low potency and reduced effect. In cases where a CYP enzyme catalyzes the conversion of a less active parent (prodrug) to a more active metabolite, induction could increase active metabolite levels to potentially toxic levels.
| Inducers of Cytochrome P450 Enzymes |
| CYP1A1 | Polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, tobacco smoke |
| CYP1A2 | PAH amines in barbequed meat, cruciferous vegetables such as Brussels sprouts, broccoli, cabbage, cauliflower, insulin, tobacco, omeprazole, phenytoin |
| CYP1B1 | PAHs, B-naphtoflavone, tobacco |
| CYP2A6 | Phenobarbitone, rifampicin |
| CYP2B6 | Phenobarbitone, rifampicin, efavirenz |
| CYP2C8 | Phenobarbitone, rifampicin |
| CYP2C9 | Secobarbitone, rifampicin |
| CYP1C19 | Carbamezepine, norethindrone, prednisone, rifampicin |
| CYP2D6 | Generally considered non-inducible. However, there is some evidence to suggest that rifampicin and dexamethasone may have an inducing effect. |
| CYP2E1 | Ethanol, acetone, isoniazid |
| CYP3A4/5 | Barbiturates, carbamazepine, glucocorticoids, phenytoin, rifampicin, St. John's wort |
