Liquid chromatography tandem mass spectrometry assay for the simultaneous determination of venlafaxine and O-desmethylvenlafaxine in human plasma and its application to a bioequivalence study.

A rapid, simple and sensitive liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for simultaneous determination of venlafaxine (VEN) and its active metabolite, O-desmethylvenlafaxine (ODV) in human plasma was developed using nadolol as internal standard (IS). The analytes and IS were extracted from 200 microl aliquots of human plasma via protein precipitation using 0.43% formic acid in acetonitrile and separated on a Hypurity cyano (50 mm x 4.6 mm, 5 microm) column. Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization technique, operating in multiple reaction monitoring (MRM) and positive ion mode. The precursor to product ion transitions monitored for VEN, ODV and IS were m/z 278.3-->58.1, 264.3-->58.1 and 310.4-->254.1, respectively. The total chromatographic runtime was 3 min with retention time for VEN, ODV and IS at 1.93, 1.50 and 1.29 min, respectively. The method was fully validated for its sensitivity, accuracy and precision, linearity, recovery, matrix effect, dilution integrity and stability studies. The linear dynamic range of 2.0-500 ng/ml was established for both VEN and ODV with mean correlation coefficient (r), 0.9994 and 0.9990, respectively. The intra-batch and inter-batch precision (%CV) in three validation batches across five concentration levels (LLOQ, LQC, MQC, HQC and ULOQ) was less than 12.6% for both the analytes. The accuracy determined at these levels was within -9.8 to +3.9% in terms of %bias. The method was successfully applied to a bioequivalence study of 150 mg venlafaxine extended release capsule formulation in 22 healthy Indian male subjects under fed condition.