Asian Journal of Pharmaceutical Analysis

Oseltamivir phosphate is licensed for the treatment of patients with influenza virus infection. Two LCMS/MS methods for simultaneous quantification of Oseltamivir and its active metabolite, oseltamivir carboxylate in human plasma were described here. After solid phase extraction sample was separated either on a reversed phase C18 column with a stepwise gradient using 0.05% formic acid and methanol or a cation-exchange column using an isocratic mobile phase (7 mM Ammonium formate, pH 3.5 ± 0.2: Methanol: 50:50, v/v). Flow rate of 1 mL/min was maintained in both cases. A triple quadrupole mass spectrometer operating in the positive ionization mode was used for detection and drug quantification. Both methods were validated over a range of 0.52ng/ml to 207.00 ng/ml for Oseltamivir and 4.08 ng/ml to 1200.00 ng/ml for Oseltamivir Carboxylate. Deuterated Oseltamivir and Oseltamivir carboxylate were used as internal standards. The accuracies and precisions for Oseltamivir were between 91–102% and 0.9 – 13.7% for all concentration levels. The accuracies and precisions for Oseltamivir carboxylate were between 88–109% and 0.5 – 8.2% at all levels. Furthermore, Oseltamivir and its metabolite were stable in plasma ex vivo for at least 191 days when stored at −20°C or below.