Simultaneous determination of clozapine, clozapine N-oxide, N-desmethylclozapine, risperidone, and 9-hydroxyrisperidone in plasma by high performance liquid chromatography with ultraviolet detection

A simple high performance liquid chromatography techniques with ultraviolet detection (HPLC-UV) method is described for the simultaneous determination of clozapine (CZP), clozapine N-oxide (CNO), N-desmethylclozapine (NCZ), risperidone (RSP) and 9-hydroxyrisperidone (9-OHRSP) in human plasma. After extraction process, the analytes were separated on a C 18 column (150 mm x 3.9 mm i.d.) by the mobile phase (methanol-water-dimethylamine, 60:40:0.04 (v: v:v)). Relative recoveries of five analytes were quantitative, The precision and accuracy of intra- and interday assays were all below 8.2% for R.S.D. and 5.6% for RE, respectively. Based on 1 ml of plasma, the limits of detection were 2.0 ng/ml for CZP, 0.2 ng/ml for CZP N-oxide, 1.0 ng/ml for NCZ, 1.0 ng/ml for RSP, and 0.5 ng/ml for 9-OHRSP (S/N = 3). The calibration curves were linear (r greater than or equal to 0.988). This method was applied to therapeutic drug monitoring of schizophrenia patients receiving CZP or RSP therapy. (C) 2002 Elsevier Science B.V. All rights reserved.