CYP2C19 and epilepsy: A recent study of 110 Japanese patients with epilepsy demonstrated that the mean serum concentration of N-desmethylclobazam was nine times higher in CYP2C19 PMs than in CYP2C19 homo EMs, and the degree of elevation in the serum N-desmethylclobazam/clobazam concentration ratio was dependent on the number of defective alleles of CYP2C19. This indicates that the CYP2C19 genotypes are associated with the serum concentration of the active metabolite of clobazam, N-desmethylclobazam [35].