MEASUREMENT OF CLOZAPINE AND NORCLOZAPINE IN PLASMA SERUM BY HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ULTRAVIOLET DETECTION

A simple method for the measurement of clozapine and its N-desmethyl m etabolite in human plasma or serum by high performance liquid chromato graphy is described. An internal standard (aqueous nortriptyline, 4 mg /L) (50 mu L) and Tris buffer (2 mol/L, pH 10.6) (100 mu L) are added to plasma/serum (200 pi) and the analytes and internal standard extrac ted into methyl tert-butyl ether (200 mu L). The extracts are analysed on a 150 mm column containing Spherisorb S5SCX using methanol contain ing ammonium perchlorate (35 mmol/L, pH 6.7) as eluent at a flow rate of 1.5 mL/min. Detection is by ultraviolet absorption (215 nm). The li mit of detection is better than 0.05 mg/L for both analytes and the in tra-assay precision (CV) for clozapine and norclozapine was 5.3 and 7. 3% at 0.5 mg/L and 2.6 and 2.8% at 1.5 mg/L, respectively. The method can be applied to the measurement of these compounds in plasma after a cute overdosage, for the assessment of compliance in patients apparent ly refractory to therapy and to identify interactions between clozapin e and other neuroleptic and antidepressant drugs which may effect toxi city.