r-138727 and thienopyridine

Prasugrel, a prodrug, is a novel and potent inhibitor of platelet aggregation in vivo. The metabolism of prasugrel and the elimination and pharmacokinetics of its active metabolite, 2-[1-[2-cyclopropyl-1-(2-fluorophenyl)-2-oxoethyl]-4-mercapto-3-piperidinylidene]acetic acid (R-138727), three inactive metabolites, and radioactivity were determined in five healthy male subjects after a single 15-mg (100 microCi) p.o. dose of [(14)C]prasugrel. Prasugrel was rapidly absorbed, and maximum plasma concentrations of radioactivity and R-138727 were achieved in 30 min, indicating rapid formation of R-138727. Prasugrel was extensively metabolized in humans, first by hydrolysis to a thiolactone, followed by ring opening to form R-138727, which was further metabolized by S-methylation and conjugation with cysteine. Total radioactivity was higher in plasma than in blood, suggesting limited penetration of prasugrel metabolites into red blood cells. Approximately 70% of the dose was excreted in the urine and 25% in the feces.

Topics: Administration, Oral; Biotransformation; Carbon Radioisotopes; Chromatography, High Pressure Liquid; Cysteine; Feces; Humans; Hydrolysis; Intestinal Absorption; Male; Methylation; Molecular Structure; Oxidation-Reduction; Piperazines; Platelet Aggregation Inhibitors; Prasugrel Hydrochloride; Prodrugs; Pyridines; Reference Values; Tandem Mass Spectrometry; Thiophenes

Prasugrel, a novel thienopyridine antiplatelet agent, undergoes rapid hydrolysis in vivo to a thiolactone, R-95913, which is further converted to its thiol-containing, pharmacologically active metabolite, R-138727, by oxidation via cytochromes P450 (P450). We trapped a sulfenic acid metabolite as a mixed disulfide with 2-nitro-5-thiobenzoic acid in an incubation mixture containing the thiolactone R-95913, expressed CYP3A4, and NADPH. Further experiments investigated one possible mechanism for the conversion of the sulfenic acid to the active thiol metabolite in vitro. A mixed disulfide form of R-138727 with glutathione was found to be a possible precursor of R-138727 in vitro when glutathione was present. The rate constant for the reduction of the glutathione conjugate of R-138727 to R-138727 was increased by addition of human liver cytosol to the human liver microsomes. Thus, one possible mechanism for the ultimate formation of R-138727 in vitro can be through formation of a sulfenic acid mediated by P450s followed possibly by a glutathione conjugation to a mixed disulfide and reduction of the disulfide to the active metabolite R-138727.

Topics: Biotransformation; Humans; Nitrobenzoates; Piperazines; Platelet Aggregation Inhibitors; Prasugrel Hydrochloride; Pyridines; Sulfhydryl Compounds; Thiophenes

Differences in the inhibition of cytochrome P450 activities among thienopyridine antiplatelet agents, ticlopidine, clopidogrel, prasugrel, and the metabolites, 2-oxo-clopidogrel, clopidogrel acid metabolite, deacetylated metabolite of prasugrel (R-95913) and the pharmacologically active metabolites of clopidogrel and prasugrel, were examined using recombinant cytochromes P450 and fluorescent probe substrates. Ticlopidine and clopidogrel inhibited CYP2B6 with IC(50) values of 0.0517+/-0.0323 microM and 0.0182+/-0.0069 microM, respectively, and inhibited CYP2C19 with IC(50) values of 0.203+/-0.124 microM and 0.524+/-0.160 microM, respectively. Ticlopidine also inhibited CYP2D6 (IC(50) of 0.354+/-0.158 microM). In contrast, 2-oxo-clopidogrel, prasugrel and R-95913 were much weaker inhibitors of CYP2B6, CYP2C19 and CYP2D6. The inhibitory effects of all the compounds tested were much weaker on the isoforms other than those indicated above. The active metabolites of clopidogrel and prasugrel and clopidogrel acid metabolite also did not affect the activities of the P450s examined.

Topics: Aryl Hydrocarbon Hydroxylases; Clopidogrel; Cytochrome P-450 CYP2B6; Cytochrome P-450 CYP2C19; Cytochrome P-450 CYP2D6 Inhibitors; Drug Interactions; Enzyme Inhibitors; Humans; Isoenzymes; Oxidoreductases, N-Demethylating; Piperazines; Platelet Aggregation Inhibitors; Prasugrel Hydrochloride; Pyridines; Thiophenes; Ticlopidine