Validation of a selective method for determination of paroxetine in human plasma by LC-MS/MS

A sensitive, robust, and selective liquid chromatographic - tandem mass spectrometric method ( LC- MS/ MS) was developed and validated for paroxetine quantification in human EDTA plasma. Methods. Sample preparation was based on liquid- liquid extraction using a mixture of ethyl acetate/ hexane ( 50/ 50; v/ v) to extract the drug and internal standard from plasma. Chromatography was performed on a C- 18 analytical column and the retention times were 1.6 and 1.7 for paroxetine and fluoxetine ( IS), respectively. The ionization was optimized using ESI(+) and selectivity was achieved by tandem mass spectrometric analysis using MRM functions, 330.0 --> 70.0 and 310 --> 43.9 for paroxetine and fluoxetine. Results. Analytical curve ranged from 0.2 to 20.0 ng/ mL. Inter- day precision and accuracy of the quality control ( QC) samples were < 15% relative standard deviation ( RSD). Analyte stability during sampling processing and storage were established. Conclusion. Validation results on linearity, specificity, accuracy, precision as well as application to the analysis of samples taken up to 120 h after oral administration of 20 mg of paroxetine in 28 healthy volunteers were found to be of good performance in bioequivalence study.