Challenges in the simultaneous quantitation of sumatriptan and naproxen in human plasma: Application to a bioequivalence study

An ultra performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method has been developed for the simultaneous determination of sumatriptan and naproxen in human plasma using naratriptan and indomethacin as the internal standards (ISs). The plasma samples were prepared by solid phase extraction on Phenomenex Strata-X cartridges using 100 μL human plasma sample. Chromatography was carried out on Waters Acquity UPLC BEH C18 (50 mm × 2.1 mm, 1.7 μm) analytical column under isocratic conditions using a mobile phase consisting of methanol–acetonitrile–4.0 mM ammonium acetate (70:10:20, v/v/v). The precursor → product ion transition for both the analytes and ISs was monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ionization mode. The method was validated over a wide dynamic concentration range of 0.050–100 ng/mL for sumatriptan and 0.050–100 μg/mL for naproxen. Matrix effect was assessed by post-column analyte infusion and the extraction recovery was >95.0% across four quality control levels for both the analytes. Stability was evaluated under different conditions including bench top, processed sample, freeze and thaw and long term. The method was applied to support a bioequivalence study of 85 mg sumatriptan + 500 mg naproxen sodium fixed dose formulation in 28 healthy Indian subjects. Assay reproducibility was demonstrated by reanalysis of 123 incurred samples.