TY - JOUR T1 - CYP2C8/9 Mediate Dapsone <em>N</em>-Hydroxylation at Clinical Concentrations of Dapsone JF - Drug Metabolism and Disposition JO - Drug Metab Dispos SP - 865 LP - 868 VL - 28 IS - 8 AU - Helen R. Winter AU - Yi Wang AU - Jashvant D. Unadkat Y1 - 2000/08/01 UR - http://dmd.aspetjournals.org/content/28/8/865.abstract N2 - Using selective cytochrome P450 (CYP) inhibitors and clinical concentrations (4 μM) of dapsone (DDS), we found a major contribution of CYP2C9 and little or no contribution (≤10%) of CYP3A4 and CYP2E1 to dapsone N-hydroxylation (DDS-NHY) in human liver microsomes. Sulfaphenazole (2.16 μM) and tolbutamide (500 μM), selective inhibitors of CYP2C9 (or 2C8/9), inhibited DDS-NHY by 48 ± 14 and 41 ± 15%, respectively. The apparent Michaelis-MentenKm values for DDS-NHY by cloned CYP2C8, CYP2C9, CYP2C18, and CYP2C19 were 75 μM, 31 μM, 25 μM, and greater than 1 mM, respectively. CYP3A4 and CYP2E1 were incapable of DDS-NHY at 4 μM DDS. S-mephenytoin (360 μM) activated DDS-NHY by human liver microsomes and by CYP2C8 by 43 ± 36 and 193 ± 16%, respectively. This activation was cytochromeb5-dependent. In contrast,S-mephenytoin inhibited DDS-NHY by CYP2C9, CYP2C18, and CYP2C19 by 27 ± 2, 49 ± 1, and 32 ± 4%, respectively. Because CYP2C18 and CYP19 are expressed at low concentrations in the human liver, these observations indicate that at clinical DDS concentrations, CYP2C9 is a major and CYP2C8 is a likely minor contributor to DDS-NHY in human liver microsomes. The American Society for Pharmacology and Experimental Therapeutics ER -