A simple and automated online SPE-LC-MS/MS method for simultaneous determination of olanzapine, fluoxetine and norfluoxetine in human plasma and its application in therapeutic drug monitoring

The olanzapine-fluoxetine augmentation strategy has been proved efficacious for treatment-resistant depression, psychotic depression and bipolar depression. To achieve efficient therapeutic drug monitoring (TDM), we develop an automated online SPE-LC-MS/MS method for the simultaneous quantification of olanzapine, fluoxetine and norfluoxetine in human plasma. After adding an internal standard of diphenhydramine and centrifugation, a 10 mL plasma sample was directly injected into the SPE cartridge. While the analytes were retained on the SPE cartridge, the endogenous materials were washed out by the loading solvent. Following the valve switching, the analytes were eluted from the SPE cartridge to the analytical column by gradient elution. The analytes were quantified using a triple-quadrupole tandem mass spectrometer. Calibration curves were linear over the concentration range of 0.25-50.00 ng mL(-1) for olanzapine, and 0.50-100.00 ng mL(-1) for fluoxetine and norfluoxetine. The intra- and inter-day precisions were within 1.17% and 4.63%. And the accuracies were between 95.60% and 101.48%. The mean matrix effect was in the range of 90.35% to 99.89% and mean recovery was in the range of 90.35% to 96.99%. This method has been successfully applied to two Chinese schizophrenia patients. The online SPE-LC-MS/MS method allows sensitive and robust quantification of olanzapine, fluoxetine and norfluoxetine for routine TDM in clinic.