Integration of Olanzapine Determinations in a HPLC-Diode Array Detection System for Routine Psychotropic Drug Monitoring

Olanzapine is an atypical antipsychotic drug now considered as a first-line agent to treat schizophrenia and psychotic mood disorders (1). Plasma concentrations indicative of a clinical response are known to be >9 μg/L (2). Knowledge of plasma concentrations, to check compliance or drug-drug interactions, is also necessary in treatment of schizophrenia (3). Moreover, olanzapine toxicity may appear at blood concentrations that are considerably lower than those observed in antidepressant-related deaths (4). Numerous publications have described the usefulness of a HPLC silica column and aqueous methanol eluents for the analysis of many basic drugs in plasma (5)(6). The use of this type of column provides more reproducible results, making it possible to obtain a sensitive HPLC-ultraviolet (UV) procedure that is easier to perform and less expensive than electrochemical (7)(8) or mass spectrometric (9) detection. We have adapted this HPLC system for routine therapeutic drug monitoring of psy- chotropic drugs (10)(11)(12). To update this system, it is important to include new antipsychotic drugs, such as olanzapine.