RT Journal Article
SR Electronic
T1 Interindividual Variation in Relative CYP1A2/3A4 Phenotype Influences Susceptibility of Clozapine Oxidation to Cytochrome P450-Specific Inhibition in Human Hepatic Microsomes
JF Drug Metabolism and Disposition
JO Drug Metab Dispos
FD American Society for Pharmacology and Experimental Therapeutics
SP 2547
OP 2555
DO 10.1124/dmd.108.023671
VO 36
IS 12
A1 Wei V. Zhang
A1 Fabrizio D'Esposito
A1 Robert J. Edwards
A1 Iqbal Ramzan
A1 Michael Murray
YR 2008
UL http://dmd.aspetjournals.org/content/36/12/2547.abstract
AB The atypical antipsychotic drug clozapine (CLZ) is effective in a substantial number of patients who exhibit treatment-resistance to conventional agents. CYP1A2 is generally considered to be the major enzyme involved in the biotransformation of CLZ to its N-demethylated (norCLZ) and N-oxygenated (CLZ N-oxide) metabolites in liver, but several studies have also implicated CYP3A4. The present study assessed the interplay between these cytochrome P450s (P450s) in CLZ biotransformation in a panel of hepatic microsomal fractions from 14 individuals. The relative activity of P450s 1A2 and 3A4 in microsomes was found to be a major determinant of the relative susceptibility of norCLZ formation to inhibition by the P450-selective inhibitors fluvoxamine and ketoconazole. In contrast, the activity of CYP3A4 alone was correlated with the susceptibility of CLZ N-oxide formation to inhibition by these agents. These findings suggest that both P450s may be dominant CLZ oxidases in patients and that the relative activities of these enzymes may determine clearance pathways. In vivo assessment of CYP1A2 and CYP3A4 activities, perhaps by phenotyping approaches, could assist the optimization of CLZ dosage and minimize pharmacokinetic interactions with coadministered drugs. The American Society for Pharmacology and Experimental Therapeutics