TY - JOUR T1 - Flavin-Containing Monooxygenase-Mediated Metabolism of<em>N-</em>Deacetyl Ketoconazole by Rat Hepatic Microsomes JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 880 LP - 886 VL - 27 IS - 8 AU - Rosita J. Rodriguez AU - Philip J. Proteau AU - Brian L. Marquez AU - Craig L. Hetherington AU - Cheryl J. Buckholz AU - Kerry L. O’Connell Y1 - 1999/08/01 UR - http://dmd.aspetjournals.org/content/27/8/880.abstract N2 - Although ketoconazole is extensively metabolized by hepatic microsomal enzymes, the route of formation and toxicity of suspected metabolites are largely unknown. Reports indicate thatN-deacetyl ketoconazole (DAK) is a major initial metabolite in mice. DAK may be susceptible to successive oxidative attacks on the N-1 position by flavin-containing monooxygenases (FMO) producing potentially toxic metabolites. Previous laboratory findings have demonstrated that postnatal rat hepatic microsomes metabolize DAK by NADPH-dependent monooxygenases to two metabolites as determined by HPLC. Our current investigation evaluated DAK’s metabolism in adult male and female rats and identified metabolites that may be responsible for ketoconazole’s hepatotoxicity. DAK was extensively metabolized by rat liver microsomal monooxygenases at pH 8.8 in pyrophosphate buffer containing the glucose 6-phosphate NADPH-generating system to three metabolites as determined by HPLC. The initial metabolite of DAK was a secondary hydroxylamine,N-deacetyl-N-hydroxyketoconazole, which was confirmed by liquid chromatography/mass spectrometry and NMR spectroscopy. Extensive metabolism of DAK occurred at pH 8.8 in pyrophosphate buffer (female 29% and male 53% at 0.25 h; female 55% and male 57% at 0.5 h; and female 62% and male 66% at 1.0 h). Significantly less metabolism of DAK occurred at pH 7.4 in phosphate buffer (female 11%, male 17% at 0.25 h; female 20%, male 31% at 0.5 h; and female 27%, male 37% at 1 h). Heat inactivation of microsomal-FMO abolished the formation of these metabolites from DAK. SKF-525A did not inhibit this reaction. These results suggest that DAK appears to be extensively metabolized by adult FMO-mediated monooxygenation. The American Society for Pharmacology and Experimental Therapeutics ER -