A Rapid and Simple Reversed-Phase HPLC–MS/MS Determination of Baloxavir in Rat Plasma and Its Application in Pharmacokinetic Study

In this study, a novel RP-HPLC–MS/MS method was developed for the accurate quantification of baloxavir in rat plasma. The analytes were retained and separated on a C18 column, and a triple-quadrupole mass spectrometer equipped with an electrospray ionization (ESI) source was applied for quantification. Baloxavir could be well retained in the C18 column under the appropriate chromatographic conditions. Using a simple protein precipitation method, the extraction recovery was about 100%, and the ME could be negligible. The method demonstrated excellent linearity (r = 0.9995) across the concentration range of 1.59 ~ 3180.00 ng/mL for baloxavir. The precision and accuracy were within acceptable limits. The lowest limit of quantification (LLOQ) was determined to be 1.59 ng/mL. This simple method was validated and successfully applied to support the pharmacokinetics study after baloxavir was administered to the Sprague–Dawley rats.