A novel bioanalytical method development and validation of pirtobrutinib in rat plasma by LC-MS/MS and its application to pharmacokinetic study

Pirtobrutinib is used to treat mantle cell lymphoma. It inhibits B cell lymphocyte proliferation and survival by binding and inhibiting Bruton's tyrosine kinase. The study aimed to develop a simple and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method to determine the concentration of pirtobrutinib in rat plasma. Pirtobrutinib was extracted from plasma by acetonitrile-mediated protein precipitation. The quantification was performed on a SCIEX QTRAP 5500 mass spectrometer with D6-pirtobrutinib as an internal standard. A Waters X-Bridge Phenyl column combined with 0.1% Trifluoroacetic acid (TFA) and acetonitrile (40:60) was employed for chromatographic separation. The precursor-to-production transitions were m / z 480.4 > 258.4 and m / z 486.3 > 264.4 for pirtobrutinib and internal standard, respectively. This method was successfully validated according to the US Food and Drug Administration guidance. The calibration curve was linear over the concentration range of 6–120 ng mL −1 with a correlation coefficient >0.999. The suggested method's percent mean accuracy varied from 95.4 to 98.1 percent for pirtobrutinib. The mean recovery was >96.29%. Pirtobrutinib was stable in rat plasma after storage under certain conditions. The validated method was demonstrated to be selective, sensitive, and reliable, and has been successfully applied to the pharmacokinetic study of pirtobrutinib in rat plasma after oral administration.