Simultaneous quantification of prodrug oseltamivir and its metabolite oseltamivir carboxylate in human plasma by LCâMS/MS to support a bioequivalence study

A simple, precise and rapid liquid chromatographyâtandem mass spectrometry (LCâMS/MS) method has been developed and validated for the simultaneous determination of oseltamivir and oseltamivir carboxylate, a neuraminidase inhibitor, using their deuterated analogs as internal standards (ISs). The method involved solid phase extraction of the analytes and ISs from 200μL human plasma with no reconstitution and drying steps. The chromatographic separation was achieved on a Symmetry C18 (100mmÃ4.6mm, 5μm) column using 10mM ammonium formate and acetonitrile (30:70, v/v) as the mobile phase in a run time of 2.0min. Quantitation of analytes and ISs were done by multiple reaction monitoring on a triple quadrupole mass spectrometer in the positive ionization mode. The linearity of the method was established in the concentration range of 0.5â200ng/mL and 2.0â800ng/mL for oseltamivir and oseltamivir carboxylate respectively. The mean extraction recovery for oseltamivir (94.4%) and oseltamivir carboxylate (92.7%) from spiked plasma samples was consistent and reproducible. The application of this method was demonstrated by a bioequivalence study in 42 healthy Indian subjects with 75mg oseltamivir phosphate capsules. The assay reproducibility was established by reanalysis of 151 incurred subject samples. Keywords: Oseltamivir, Oseltamivir carboxylate, LC-MS/MS, Human plasma, Bioequivalence study