Determination of venlafaxine in plasma and brain tissue by HPLC

Objective: To develop an assay for venlafaxine in plasma and brain tissue by reverse-phase high performance liquid chromatography(HPLC).Methods: Venlafaxine was extracted both from rat plasma and brain tissue samples with liquid-phase extraction-hexane-isoamylalcohol(99∶1;v/v).The mobile phase consisted of acetonitrile-phoshpate buffer(25∶75) at a flow rate of 1.4 ml/min.The compound was detected at 229 nm.Results: A linear plot of plasma venlafaxine versus peak area was within the range of 0.25-32 μg/ml,and a linear range of brain tissue venlafaxine was 0.05-6.40 μg/ml.The lowest concentration of quantification for venlafaxine in plasma was 0.15 μg/ml.The average recovery of venlafaxine in plasma was 89.4%with the intra-day SD of 3.7-5.5%,1.6-5.2%,4.2-5.7% and inter-day SD of 6.5%,5.0%,2.0% at the concentrations of 0.5,4.0,32.0 μg/ml,respectively.The lowest concentration of quantification for venlafaxine in brain tissue was 0.25 μg/ml,The average recovery in brain tissue was 93.3% with the intra-day SD of 2.2-3.4%,1.3-6.0%,0.6-3.4% and inter-day SD of 4.1%,3.4%,5.6% at the concentrations of 0.5,4.0,32.0 μg/ml,respectively.Conclusion: A specific HPLC assay for venlafaxine in plasma and brain tissue was developed.It offers pharmacokinetic studies and brain tissue concentration monitoring in rats.