Clobazam metabolism by c DNA-expressed human CYP

Abstract

Objective Clobazam (CLB) is a 1,5 benzodiazepine effective as antiepileptic agent, mainly as add-on therapy in patients with refractory epilepsy. The aim of the study was to determine the main cytochromes P450 (CYP) involved in the metabolism of clobazam. Methods cDNA-expressed human CYP (1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C18, 2C19, 2D6, 2E1, 3A4, 3A5 and 3A7) were used in vitro. Kinetic parameters Km and Vm were calculated for the main metabolic pathways. Inhibition studies were conducted in human liver microsomes with specific inhibitors (furafylline, thiotepa, sulfaphenazole, omeprazole, quinidine, chlorzoxazone, and ketoconazole). Results CLB was mainly metabolized into desmethylclobazam (NCLB) by CYP3A4 and CYP2C19 (Km=29.0 and 31.9μM, Vm=6.20 and 1.15 nmol/min/nmolCYP, Vm/Km=214 and 36.1nmol/min respectively). NCLB was subsequently metabolized to hydroxy-desmethylclobazam (OH-NCLB) by CYP2C19 (Km = 5.74 μM, Vm=0.219, Vm/Km=38.2 nmol/min). Hydroxylation of CLB into hydroxyclobazam and demethylation of hydroxyclobazam into hydroxy-desmethylclobazam were minor pathways. The demethylation of CLB was inhibited by ketoconazole (1μM) at 74%, omeprazole (10μM) at 21% and thiotepa (10μM) at 20%. The hydroxylation of NCLB was inhibited by omeprazole (10μM) at 55% and ketoconazole (1μM) at 29%. Conclusion For the first time, the main metabolic pathways of clobazam were characterized: main pathways were demethylation of CLB by CYP3A4 and CYP2C19 and hydroxylation of NCLB by CYP2C19. Clinical Pharmacology & Therapeutics (2004) 75, P37–P37; doi: 10.1016/j.clpt.2003.11.140