Liquid chromatography tandem mass spectrometry method for the simultaneous stereoselective determination of venlafaxine and its major metabolite, O-desmethylvenlafaxine, in human plasma.

A sensitive, accurate and highly stereoselective assay for the simultaneous determination of venlafaxine (VEN) and its equipotent metabolite, O-desmethyl venlafaxine (ODV), in human plasma was developed and validated. Analytes were simultaneously extracted from plasma using solid-phase extraction and detected by tandem mass spectrometry in positive ion mode with a turbo ion spray interface. Deuterium-labeled VEN and ODV were used as internal standards. Chromatographic separation was performed on a Chiral AGP column, using a time programmed gradient flow with a total run time of 16 min. The method has a lower limit of quantitation of 0.60 ng/mL. The assay was linear over a range 0.60-300.00 ng/mL for both the enantiomers of VEN and ODV, respectively, with coefficient of correlation > 0.99. The extraction recoveries were >77.0% on an average for all the four analytes. The analytes were found stable in plasma through three freeze (-15 °C) and thaw cycles and under storage at room temperature for 8 h, and also in mobile phase at 10 °C for 54 h. The method has shown good reproducibility, with intra- and inter-day variation coefficients < 9%, for all the analytes, and has proved to be very reliable for analysis of VEN and its metabolite in clinical study samples.