Effect of Felbamate on The Pharmacokinetics of Clonazepam

To assess the possible interaction between clonazepam and felbamate, a double-blind, randomized, placebo-controlled, two-way crossover study was conducted in 18 healthy male volunteers. Volunteers were administered clonazepam (1 mg q12h) and felbamate (1200 mg q12h) or matching placebo for 10 days during each period of the crossover. Following morning dosing on day 10, blood samples were obtained over 12 h for the determination of clonazepam and the metabolites 7-amino-clonazepam and 7-acetamido-clonazepam. Felbamate increased clonazepam's C(max) and AUC(0--12 h) by 17% and 14%, respectively (p < 0.01). The 90% confidence intervals following log-transformation for each of these pharmacokinetic parameters were within the generally accepted interval (80--125%) for bioequivalence. Felbamate had no significant effect on the pharmacokinetics of 7-amino-clonazepam, whereas 7-acetamido-clonazepam concentrations were below the limit of quantification in all but one subject. Adverse events were mainly central nervous system in nature, with a greater incidence reported during coadministration with felbamate compared with placebo. Overall, felbamate appears to have no clinically relevant effects on the pharmacokinetics of clonazepam.