| Summary: | Abstract Larotrectinib is an orally administered drug and the first and only selective pan-tropomyosin receptor kinase (TRK) inhibitor in clinical development to treat cancer patients harboring a neurotrophic receptor tyrosine kinase gene fusion. In this study, an analytical method to quantify the TRK inhibitor in mouse and human plasma was developed and validated using LC-MS/MS following protein precipitation with acetonitrile. Larotrectinib and an internal standard (carbamazepine) were separated from endogenous substances using an Xterra C18 column with acetonitrile containing 0.1% formic acid as the mobile phase. The ions m/z 429.8 → 342.8 for larotrectinib and m/z 237.0 → 194.0 for carbamazepine detected in multiple reaction monitoring mode were used for the quantitation. The detector response of larotrectinib was linear within the concentration range 5–10,000 ng/mL with a correlation coefficient (r 2) of not less than 0.999. The intra- and inter-day precision and accuracy were less than 10.48% and within − 8.99%, respectively, in mouse and human plasma. Larotrectinib was stable under various storage and handling conditions, and no significant matrix effect was observed in both mouse and human plasma. Finally, the assay was successfully applied to the pharmacokinetic study of larotrectinib after its intravenous and oral administration to mice.
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