Enzyme induction occurs when chemicals cause an increase in the synthesis and activity of an enzyme. This leads to increased metabolism of drugs that are catalyzed by that enzyme.
When one drug causes an increased rate of metabolism of another drug by inducing the CYP enzyme involved in the biotransformation of that drug, there is a resultant effect on the drug’s efficacy. The parent drug is metabolized at an accelerated rate, 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 be responsible for increasing 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-inducable, however, there is some evidence to suggest that rifampicin and dexamethasone may have an inducing effect. |
| CYP2E1 | Ethanol, acetone, isoniazid |
| CYP3A4/5 | Barbituates, carbamazepine, glucocorticoids, phenytoin, rifampicin, St. John's wort |
