a cytochrome P450 isoform found in the gastrointestinal tract as well as hepatic and other cells; substrates include benzodiazepines, calcium channel blockers, antihistamines, steroid hormones, and protease inhibitors. Inhibited by antidepressants, azole antifungals, cimetidine, grapefruit juice, and erythromycin. Induced by phenobarbital, phenytoin, rifampin, and carbamazepine.
