Interactions of imidazole antifungal agents with purified cytochrome P-450 proteins

The imidazole N-substituted antifungal agents ketoconazole, miconazole and clotrimazole have been shown to be potent inhibitors of oxidative metabolism by both a phenobarbital-induced cytochrome P-450 (P-450 b) and a 3-methylcholanthrene-induced cytochrome P-448-protein (P-450 c) in reconstituted systems. All three compounds inhibited the cytochrome P-450 b-dependent 7-pentoxyresorufin- O-dealkylase and the cytochrome P-450 c-dependent 7-ethoxyresorufin- O-deethylase activities. When 7-benzyloxyresorufin and 7-ethoxycoumarin were employed as substrates with both cytochrome preparations, all three antifungal compounds exhibited selective inhibition of the cytochrome P-450 b preparation; ketoconazole was always the weakest inhibitor. The three antifungal agents were also shown to elicit a type II difference spectral interaction with both isoenzymes, the magnitude of the spectral interaction being greater with the cytochrome P-450 b preparation.