Liquid chromatography determination of clobazam and its major metabolite N-desmethylclobazam in human plasma.

A specific procedure for the analysis of clobazam and N-desmethylclobazam in plasma is described. Reversed-phase liquid chromatography was performed on a Radial-pak cartridge using a mixture of 45% acetonitrile and 55% buffer solution (pH 7); the ultraviolet detector was set at 254 nm. The method used diazepam as internal standard and diethylether as extraction solvent. The calibration curves are linear between 50 and 500 ng/ml for clobazam and between 100 and 1000 ng/ml for N-desmethylclobazam. The day-to-day precision of the procedure at clobazam plasma concentrations of 50, 250, and 500 ng/ml generated coefficients of variation of 2.2, 6.6, and 11.3%, respectively. No interference occurred in plasma from patients treated with various drugs. The method has been used to study the pharmacokinetics of clobazam and N-desmethylclobazam in patients receiving oral clobazam.