Comparison of the pharmacodynamic effects of the platelet ADP receptor antagonists clopidogrel and AR-C69931MX in patients with ischaemic heart disease.

We compared the antiplatelet effects of clopidogrel and the intravenous platelet P2Y(12) receptor antagonist AR-C69931MX, which acts on the same receptor as clopidogrel by a different and reversible mechanism and, unlike clopidogrel, is active in vitro. Thirteen patients with acute coronary syndromes entered into a phase II study of intravenous AR-C69931MX (Group 1) and eight patients undergoing intracoronary stent implantation and treated with clopidogrel (Group 2) were studied using a whole blood single-platelet counting aggregation assay. Group 2 patients were also studied using turbidimetry with ADP and TRAP as agonists and whole blood [(14)C]5HT release to study dense granule secretion in response to ADP, collagen and TRAP. In Group 2 studies, a therapeutic concentration of AR-C69931MX was added in vitro before and after clopidogrel administration. AR-C69931MX in Group 1 achieved greater inhibition of ADP-induced platelet aggregation than clopidogrel in Group 2 and AR-C69931MX in vitro added to the effects of clopidogrel on ADP-induced aggregation. AR-C69931MX but not clopidogrel inhibited TRAP-induced aggregation and granule secretion and AR-C69931MX had a more consistent inhibitory effect on collagen-induced responses. In conclusion, therapeutic administration of clopidogrel moderately inhibits platelet P2Y(12) receptor activation and substantially greater P2Y(12) receptor blockade can be achieved with AR-C69931MX.