LC-triple quadrupole-MS based quantitative analysis of tafenoquine in rat plasma and red blood cells: method development and validation.

BACKGROUND: For antimalarial drugs such as Tafenoquine, which preferentially distribute within red blood cells (RBCs), plasma concentrations cannot accurately reflect intracellular drug levels available to exert the therapeutic effect. METHODOLOGY: This study aims to establish a sensitive bioanalytical method using LC-triple quadrupole-MS for the accurate quantification of Tafenoquine levels in red blood cells (RBCs) and plasma, addressing the lack of previously reported methods. A simple protocol for the isolation of a 99% pure RBC fraction, with minimal blood volume requirements, was also established to carry out this study. Across both the biological matrices, the assay represented a linear dynamic range of 0.5-800 ng/mL and a lower limit of quantification of 0.5 ng/mL. RESULTS: Precision and accuracy for the developed method were found within the acceptable range of the ICH M10 guideline across both matrices for the entire calibration range. Matrix effect, recovery and stability studies also gave promising results for RBCs as well as the plasma matrix. CONCLUSION: The method will allow accurate evaluation of cellular-level pharmacokinetics, drug-drug interactions, and bioavailability of Tafenoquine, providing a strong foundation for antimalarial drug discovery research in a preclinical setup.