Simultaneous determination of clobazam and its major metabolite in human plasma by a rapid HPLC method

A rapid and specific HPLC method has been developed and validated for simultaneous determination of clobazam, the anticonvulsant agent, and its major metabolite in human plasma. The sample preparation was a liquid–liquid extraction with tuloene yielding almost near 100% recoveries of two compounds. Chromatographic separation was achieved with a Chromolith™ Performance RP-18e 100 mm × 4.6 mm column, using a mixture of a phosphate buffer (pH 3.5; 10 mM)–acetonitrile (70:30, v/v), in isocratic mode at 2 ml/min at a detection wave-length of 228 nm. The calibration curves were linear (r2 > 0.998) in the concentration range of 5–450 ng ml−1. The lower limit of quantification was 5 ng ml−1 for two compounds studied. The within- and between-day precisions in the measurement of QC samples at four tested concentrations were in the range of 0.89–9.1% and 2.1–10.1% R.S.D., respectively. The developed procedure was applied to assess the pharmacokinetics of clobazam and its major metabolite following administration of a single 10 mg oral dose of clobazam to healthy volunteers.