Background: Shear-induced platelet aggregation (SIPA) is an important mechanism of thrombosis at arterial bifurcations or stenotic lesions. Methods: We investigated the in vitro effects of dipyridamole (DP) and acetylsalicyclic acid (ASA) on SIPA in whole blood and platelet-rich plasma (PRP). Results: In whole blood, DP 20 µM significantly inhibited SIPA, while DP 5 µM or ASA 5 or 20 µM did not. SIPA in whole blood was, however, significantly inhibited by the combination of 5 or 20 µM of DP and ASA. SIPA in PRP was not inhibited by any concentration of DP or ASA, alone or in combination. Conclusions: These results suggest that DP has an effect on red blood cells and that ASA enhances the inhibitory effect of DP on SIPA in whole blood. These effects may be related to the additive effect of combination therapy with DP and ASA on stroke prevention.

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