Magnitude and time course of platelet inhibition with extended release dipyridamole with or without aspirin in healthy Japanese volunteers

Randomized trials showed greater stroke prevention with extended release dipyridamole in combination with low dose aspirin than with either aspirin or dipyridamole alone. However, most studies with this formulation (Aggrenox) were carried out in Europe and North America. Considering potential inter-racial differences in drug response, we conducted a small randomized study in healthy Japanese volunteers to compare antiplatelet regimens with regard to the changes in the platelet biomarkers. Thirty healthy volunteers (18-40 years old, 15 male and 15 female) of Japanese descent were randomized to Aggrenox (n = 17) or aspirin 81 mg (n = 13 volunteers) for 30 days. Platelet function was assessed at baseline, and on days 15, and 30 by conventional aggregometry, whole blood flow cytometry, and cartridge-based analyzer. Both Aggrenox and aspirin provided sustained platelet inhibition at Day 15 and Day 30. Therapy with Aggrenox, however, was associated with more prominent and significant inhibition of collagen-induced aggregation (p = 0.08, Day 15), as well as prolongation of the closure time (p = 0.001, Day 30); diminished expression of platelet endothelial cell adhesion molecule-1 (PECAM-1) (p = 0.02, Day 30), glycoprotein IIb (GPIIb) antigen (p = 0.001 and 0.024 for Day 15 and Day 30), and GPIIb/IIIa activity by PAC-1 antibody (p = 0.014 and 0.03), CD62 (P-selectin) (p = 0.03 for Day 15 and Day 30), as well as inhibition of protease activated receptors (PAR-1) associated with intact WEDE-15 (p = 0.002 and 0.003) and SPAN-12 (p = 0.002 and 0.04) thrombin receptors when compared with aspirin. The magnitude and durability of platelet response after Aggrenox in healthy Japanese is similar to those effects observed in Caucasians and African-Americans. A larger study to assess drug efficacy and safety in the Japanese post-stroke patients is warranted.