Development and validation of an ultra‐performance liquid chromatography–tandem mass spectrometry method for the determination of baloxavir in rat plasma and its application to pharmacokinetic studies

Abstract In this study, an ultra‐performance liquid chromatography–tandem mass spectrometry method was established for the development and validation of baloxavir acid (BXA) concentrations and the active ingredients of the antiviral drug baloxavir marboxil (BXM). Further, the method was applied to study the pharmacokinetics of BXA. BXA was determined by the electrospray ionization multiple reaction monitoring positive ion mode, and the mass‐to‐charge ratios ( m/z ) of BXA and internal standard baloxavir‐d4 were 484.2 → 247.2 and 488.1 → 247.2. An Oasis max online column (2.1 × 20 mm, 30 μm) was used with 1% formic acid in water (A) and 2% formic acid in acetonitrile (B) as mobile phases at a flow rate of 0.5 mL·min −1 for chromatographic separation. The linearity was good in the range of 3–200 ng·mL −1 (r = 0.9994), with 3.00 ng·mL −1 lower limit of quantification. The relative standard deviation of the inter‐assay precision was less than or equal to 6.51%, and the accuracy was in the range of 91.28%–104.29%. This method is suitable for the determination of BXA and for performing pharmacokinetic studies in clinical research.