Determination of thiorphan, a racecadotril metabolite, in human plasma by LC-MS/MS and its application to a bioequivalence study in Chinese subjects

The objective of this study was to use LC-MS/MS to compare the pharmacodynamic properties and bioequivalence of two 200-mg formulations of racecadotril: suspension formulation (test) and granule formulation (reference) in healthy Chinese subjects.A single-dose, randomized, two-period crossover study was conducted in fasted healthy Chinese subjects, who received a single oral dose of the test or reference formulation, followed by a 7-day washout period and administration of the alternate formulation.The rapid and highly sensitive LC-MS/MS method exhibited a reasonable linearity range (2.324 - 952.000 ng/mL) and high sensitivity (LLOQ of 2.324 ng/mL). The within- and between-run precision, accuracy, and stability results were within the acceptable limits, and no matrix effect was observed. The 90% CI of the ratio of geometric means for AUC0-t, AUC0-∞, and Cmax were 88.1 - 102.3%, 87.9 - 101.5% and 99.5 - 113%, respectively, which met the regulatory criteria for bioequivalence.The method is suitable for quantification of thiorphan in human plasma. In addition, the results indicated that the test and reference formulations were bioequivalent in terms of both rate and extent of absorption.