Journal of Chromatography B, 755 (2001) 349–354 www.elsevier.com / locate / chromb Short communication Determination of clozapine and its N-desmethyl metabolite by high-performance liquid chromatography with ultraviolet detection 1 * ´ ´ ´ Adrian LLerena , Roland Berecz , Marıa Jesus Norberto, Alfredo de la Rubia Unit of Research and Clinical Psychopharmacology, Department of Pharmacology and Psychiatry, Faculty of Medicine, University of Extremadura, Avda. de Elvas s / n 06071 Badajoz, Spain Received 20 April 2000; received in revised form 5 January 2001; accepted 19 January 2001 Abstract A rapid high-performance liquid chromatographic method has been developed for the simultaneous determination of the atypical antipsychotic drug clozapine and its principal metabolite, N-desmethyl clozapine in human plasma. After liquid–liquid extraction the compounds were separated in a reversed-phase column and measured by ultraviolet absorption at 230 nm. For both compounds inter-day variations were ,3.8%, and, based on a plasma sample volume of 2 ml, the limits of quantification were 25 ng / ml. Analytical interference from coadministered psychoactive drugs and their metabolites was also studied, and no interference was found from the most commonly used antidepressants and antipsychotic drugs. The assay is sufficiently sensitive and easy to use for the analysis of plasma samples in human clinical trials and therapeutic drug monitoring.  2001 Elsevier Science B.V. All rights reserved. Keywords: Clozapine; N-desmethyl clozapine 1. Introduction drug in the treatment of psychosis [2]. However, despite these advantages, its use has been severely Clozapine is an atypical antipsychotic agent with a limited by the occurrence of agranulocytosis in 1– dibenzodiazepine structure (Fig. 1). Unlike conven- 2% of the patient population [1,3]. tional neuroleptics, clozapine is less likely to cause extrapyramidal side-effects [1]. The use of clozapine has a substantial impact on the management of psychotic disorders: over 30% of patients who are otherwise non-responsive or intolerant of standard neuroleptic therapy respond to this drug, which is therefore of major importance as a second-choice *Corresponding author. Tel.: 134-924-289-467; fax: 134-924- 289-467. E-mail address: allerena@unex.es (A. LLerena). 1 Present address: University of Debrecen, Medical and Health Science Center, Department of Psychiatry, Debrecen, Hungary. Fig. 1. Chemical structure of clozapine. 0378-4347 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0378-4347(01)00056-1