Kinetic degradation study for the first licensed anti‐influenza polymerase inhibitor, baloxavir marboxil, using high‐performance liquid chromatography‐mass spectrometry

The first licensed polymerase inhibitor, baloxavir marboxil was recently approved for the treatment of influenza A and B viruses. Furthermore, there is growing interest in testing the antiviral activity of baloxavir marboxil against Coronavirus. Despite its critical clinical value, there is no information on the degradation products, pathways, or kinetics of baloxavir marboxil under various stress conditions. In this study, a new high‐performance liquid chromatography‐ultraviolet detection method for accurately quantifying baloxavir marboxil in the presence of its degradation products was developed. A study of degradation kinetics revealed that acidic, thermal neutral, and photolytic degradation reactions have zero‐order kinetics, whereas basic and oxidative degradation reactions have first‐order kinetics. The structural characterization of baloxavir marboxil degradation products was performed by coupling the optimized high‐performance liquid chromatography method to the triple‐quadrupole tandem mass spectrometer. The proposed approach was validated according to the International Council for Harmonisation Q2 (R1) requirements for accuracy, precision, robustness, specificity, and linearity. The validated new method was successfully used to analyze baloxavir marboxil as raw material and its pharmaceutical dosage form, Xofluza.