Applicability of an Assay for Routine Monitoring of Highly Variable Concentrations of Olanzapine Based on HPLC with Mass Spectrometric Detection

The thienobenzodiazepine derivative olanzapine (OLZ) is a commonly used antipsychotic drug that has demonstrated efficacy against both positive and negative symptoms of schizophrenia (1).OLZ shows variable pharmacokinetics, with induction of the CYP1A2 enzyme by cigarette smoking being one of the most important factors contributing to this variability (2). Moreover, because of the potential toxicity of OLZ at relatively low concentrations, monitoring of OLZ has been suggested to be necessary (3).Several methods have been developed to measure OLZ in whole blood, plasma, or serum, including HPLC-based techniques (4)(5)(6)(7)(8)(9)(10), liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) (11)(12)(13), and gas chromatography coupled with MS (14).The goal of this work was to develop a rapid and technically simple assay based on LC coupled with electrospray MS that would be capable of routinely determining extremely low OLZ concentrations. This could be very useful for monitoring schizophrenic patients who are heavy smokers, a group that accounts for 70–90% of these patients (15), who are more likely to display lower OLZ concentrations than nonsmokers (2)(16).The chromatographic system used consisted of a Hewlett-Packard (HP) 1100 series equipment (Agilent Technologies Spain S.L.) with a degasser (Model G1322A), quaternary pump (Model G1311A), autosampler (Model G1313A), ultraviolet/visible detector (Model G1315A) set at 260 nm wavelength, and a quadrupole mass spectrometer (model G1946A). A computer-assisted HP G2710AA LC/MS ChemStation (Agilent Technologies Spain S.L.) was used to operate the modules and facilitate data management.Blood samples were collected in tubes containing EDTA, and plasma was immediately separated after centrifugation and stored frozen at −20 °C until assayed. To avoid OLZ oxidation during storage and manipulation (6), we added 5 μL of a 250 g/L ascorbic acid …