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

Abstract

A simple, precise and rapid liquid chromatography-tandem mass spectrometry (LC-MS/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 200 μL human plasma with no reconstitution and drying steps. The chromatographic separation was achieved on a Symmetry C18 (100 mm×4.6 mm, 5 μm) column using 10 mM ammonium formate and acetonitrile (30:70, v/v) as the mobile phase in a run time of 2.0 min. 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 0.5-200 ng/mL and 2.0-800 ng/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 75 mg oseltamivir phosphate capsules. The assay reproducibility was established by reanalysis of 151 incurred subject samples.

Keywords: Bioequivalence study; Human plasma; LC-MS/MS; Oseltamivir; Oseltamivir carboxylate.

Fig. 1

Q3 mass spectra of (A) oseltamivir (OST, m/z 313.1→166.2, scan range 50–360 amu) and (B) oseltamivir carboxylate (OSTC, m/z 285.1→138.1, scan range 50–360 amu) in the positive ionization mode.

Fig. 2

Representative chromatograms of (A–D) oseltamivir (m/z 313.1→166.2) and oseltamivir-d5 (IS-1, m/z 318.1→171.2) and (E–H) oseltamivir carboxylate (m/z 285.1→138.1) and oseltamivir acid-C13-d3 (IS-2, m/z 289.2→138.3) in (A) & (E) double blank plasma, (B) & (F) blank plasma spiked with IS, (C) & (G) analytes at LLOQ and IS, (D) & (H) real subject sample at C_max after administration of 75 mg dose of oseltamivir phosphate.

Fig. 3

MRM LC–MS/MS chromatograms of blank plasma extract with post column infusion of (A) oseltamivir, (B) oseltamivir carboxylate, (C) oseltamivir-d5 and (D) oseltamivir acid-C13-d3.

Fig. 4

Mean plasma concentration-time profile of (A) oseltamivir and (B) oseltamivir carboxylate after oral administration of test (75 mg oseltamivir phosphate capsule of an Indian Company) and a reference (TAMIFLU^®, 75 mg oseltamivir phosphate capsule from Genentech USA Inc., USA) formulation to 42 healthy Indian subjects under fed conditions.