Quantitation of clobazam in human plasma using high-performance liquid chromatography.

A rapid and simple reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of clobazam concentrations in human blood samples is developed and validated. Solid-phase column extraction is performed to clean up blood samples before running the analytical HPLC system. The chromatography is isocratic with a mobile phase consisting of acetonitrile (20%, v/v), methanol (23%, v/v), and 0.1 M potassium hydrogen phosphate buffer (pH 3.6; 57%, v/v) at a constant flow rate of 2 mL/min. Clobazam is detected at 226 nm. Chromatography is completed within less than 25 min. The recovery rate is greater than 95% and linear over a wide range of drug concentrations. The intra-assay coefficient of variation percentage varies between 4.3 and 12. This method is used for therapeutic drug monitoring in patients undergoing antiepileptic therapy with clobazam. Plasma levels of clobazam ranged from 21 to 663 ng/mL. Other antiepileptic compounds, such as clonazepam and phenobarbital, did not interfere with the detection of clobazam.