Rapid quantification of mirtazapine and desmethyl mirtazapine in human plasma by LC–ESI-MS/MS: Application to a bioequivalence study

A high-throughout bioanalytical method based on a solid-phase extraction (SPE), and rapid liquid chromatography–tandem mass spectrometry (LC–MS/MS) analysis has been developed and validated for the quantification of mirtazapine (MRT) and desmethyl mirtazapine (DMRT) in heparinized human plasma. Plasma samples, without a drying and reconstitution step, were extracted by a simple SPE. The analytes and imipramine (internal standard, IS) chromatographed on a Betasil-C18 column. The total chromatographic run time was 1.8 min per sample. Response was a linear function of concentration in the range 0.1–100.0 ng/ml, with correlation coefficient ⩾0.9994. The assay has excellent characteristics and has been successfully applied to bioequivalence study samples for estimation of MRT and DMRT in healthy human subjects.