PT  - JOURNAL ARTICLE
AU  - Giraud, Carole
AU  - Tran, Agnès
AU  - Rey, Elisabeth
AU  - Vincent, Jean
AU  - Tréluyer, Jean-Marc
AU  - Pons, Gérard
TI  - IN VITRO CHARACTERIZATION OF CLOBAZAM METABOLISM BY RECOMBINANT CYTOCHROME P450 ENZYMES: IMPORTANCE OF CYP2C19
AID  - 10.1124/dmd.32.11.1279
DP  - 2004 Nov 01
TA  - Drug Metabolism and Disposition
PG  - 1279--1286
VI  - 32
IP  - 11
4099  - http://dmd.aspetjournals.org/content/32/11/1279.short
4100  - http://dmd.aspetjournals.org/content/32/11/1279.full
SO  - Drug Metab Dispos2004 Nov 01; 32
AB  - The specific cytochrome P450 (P450) isoforms mediating the biotransformations of clobazam (CLB) and those of its major metabolites, N-desmethylclobazam (NCLB) and 4′-hydroxyclobazam were identified using cDNA-expressed P450 and P450-specific chemical inhibitors. Among the 13 cDNA-expressed P450 isoforms tested, CLB was mainly demethylated by CYP3A4, CYP2C19, and CYP2B6 and 4′-hydroxylated by CYP2C19 and CYP2C18. CYP2C19 and CYP2C18 catalyzed the 4′-hydroxylation of NCLB. The kinetics of the major biotransformations were studied: CYP3A4, CYP2C19, and CYP2B6 mediated the formation of NCLB with Km = 29.0, 31.9, and 289 μM, Vmax = 6.20, 1.15, and 5.70 nmol/min/nmol P450, and intrinsic clearance (CLint) = 214, 36.1, and 19.7 μl/min/nmol P450, respectively. NCLB was hydroxylated to 4′-hydroxydesmethylclobazam by CYP2C19 with Km = 5.74 μM, Vmax = 0.219 nmol/min/nmol P450, and CLint = 38.2 μl/min/nmol P450 (Hill coefficient = 1.54). These findings were supported by chemical inhibition studies in human liver microsomes. Indeed, ketoconazole (1 μM) inhibited the demethylation of CLB by 70% and omeprazole (10 μM) by 19%; omeprazole inhibited the hydroxylation of NCLB by 26%. Twenty-two epileptic patients treated with CLB were genotyped for CYP2C19. The NCLB/CLB plasma metabolic ratio was significantly higher in the subjects carrying one CYP2C19*2 mutated allele than in those carrying the wild-type genotype. CYP3A4 and CYP2C19 are the main P450s involved in clobazam metabolism. Interactions with other drugs metabolized by these P450s can occur; moreover, the CYP2C19 genetic polymorphism could be responsible for interindividual variations of plasma concentrations of N-desmethylclobazam and thus for occurrence of adverse events. The American Society for Pharmacology and Experimental Therapeutics