Ketoconazole: a potent inhibitor of cytochrome P-450-dependent drug metabolism in rat liver.

Ketoconazole, an orally active imidazole antimycotic agent, is shown to be a potent inhibitor of drug N-demethylase activities of liver microsomes from rats pretreated with phenobarbital or pregnenolone-16 alpha-carbonitrile, and an inhibitor of 7-ethoxyresorufin O-deethylase activity of liver microsomes from rats pretreated with 5,6-benzoflavone. Spectrophotometric studies reveal that the imidazole compound binds to the cytochrome P-450 component of the monooxygenase complex, and has little effect on NADPH-cytochrome c (P-450) reductase activity. These results are strongly suggestive that cytochrome P-450 is the site of action of this potent inhibitor of drug metabolism in liver microsomes.