Assay for quantitation of clozapine and its metabolite N-desmethylclozapine in human plasma by high-performance liquid chromatography with ultraviolet detection

A high-performance liquid chromatographic method with UV detection has been developed for the analysis of clozapine and its active N-desmethylated metabolite (N-desmethylclozapine = DMC) in human plasma. A liquid/liquid procedure was used to extract clozapine and DMC from human plasma. The analysis was performed on a Cs Nucleosil column and the mobile phase comprised acetonitrile-water-Pic B5 diethylamine (63:37:25:0.04, v/v/v/v). The detection wavelength was 245 nm. The intra-assay and inter-assay precision was satisfactory within the concentration range 10-900 ng ml(-1). The lower detection limit for clozapine and for DMC was 5 ng ml(-1). The recovery and reproducibility values of this method were better or similar to those found by other authors. This method, which is simple, selective and avoids an evaporation step, can be used routinely for therapeutic drug monitoring. (C) 1997 Elsevier Science B.V.