Improved selectivity for high-performance liquid chromatographic determination of clonazepam in plasma of epileptic patients

We report a high-performance liquid chromatography method for clonazepam de termination in plasma. The use of a synthetic silica-based stationary phase markedly improved clonazepam resolution compared to standard reversed-phas e columns. A liquid-liquid extraction was used, associated with reversed-ph ase chromatography, gradient elution and ultraviolet detection. Accuracy an d precision were satisfactory at therapeutic concentrations. Selectivity wa s studied for benzodiazepines or other antiepileptic drugs, with particular attention to newly marketed drugs i.e., gabapentine and vigabatrin. No int erfering substance was evidenced. Under the conditions described, it was po ssible to quantify clonazepam at nanogram level even when carbamazepine was present at therapeutic concentrations. (C) 1998 Elsevier Science B.V. All rights reserved.