Stereoselective metabolism of prasugrel in humans using a novel chiral liquid chromatography-tandem mass spectrometry method.

A liquid chromatography-tandem mass spectrometry method was developed to chromatographically separate the four stereoisomers of the active metabolite of prasugrel, R-138727, in human plasma after derivatization with bromomethoxyacetophenone to stabilize the molecule. This technique was designed to determine the relative contribution of each stereoisomer, based on statistical analyses of each stereoisomer's chromatographic peak areas. The methodology was validated and used for the analysis of clinical samples in which R-138727 had been derivatized at the time of blood collection. This technique can be useful to determine the ratios of stereoisomers in biological samples (e.g., plasma) especially in situations in which authentic standards of each individual stereoisomer are scarce or unavailable. In humans, the metabolic formation of R-138727 from prasugrel was found to be stereoselective, where 84% of R-138727 was present as RS and RR, the two most pharmacologically potent isomers, whereas the SR and SS enantiomers accounted for approximately 16%. The ratios of the R-138727 stereoisomers were consistent among subjects, regardless of the dose or time of sample collection or whether the blood was sampled after the first dose or after 4 weeks of therapy.