Incurred sample reanalysis of fingolimod and fingolimod phosphate in blood: stability evaluation and application to a rat pharmacokinetic study

Abstract

Background: Incurred sample reanalysis (ISR) is an in-study validation parameter, which reinforces that the validated bioanalytical methods are reproducible. ISR of whole blood samples is complex when the test compounds can interconvert, ex vivo. Fingolimod and fingolimod phosphate are highly distributed in the blood cellular components and undergo rapid interconversion, both in vivo and ex vivo. An LC–MS/MS method capable of simultaneous quantification of fingolimod and fingolimod phosphate with the controlled sample preparation procedure is essential. Results: The ex vivo analyte interconversion in blood was controlled by lysing the blood cells. Conclusion: Lysis of blood samples not only controlled the interconversion but also rendered homogeneity to the sample, which led to acceptable ISR results from the study.