Background: Previous studies have shown the potential benefit of using antiplatelet agents with complementary modes of action. Methods: Using a crossover design, the ex vivo antiplatelet effects of 10 days’ treatment with clopidogrel 75 mg + acetylsalicylic acid (ASA) 75 mg daily, ASA 75 mg/day, or extended-release dipyridamole 200 mg/low-dose ASA 25 mg twice daily were compared, using various platelet agonists. Results: Clopidogrel + ASA was significantly more effective than dipyridamole + ASA in inhibiting collagen-induced platelet aggregation in whole blood (mean 44.9 ± 5.6% inhibition vs. 16.5 ± 6.7%; p = 0.0009). Clopidogrel + ASA was significantly more effective than ASA or dipyridamole + ASA in inhibiting ADP-induced platelet aggregation in whole blood (p≤ 0.0001) and platelet-rich plasma (PRP) (p≤ 0.0001), and in inhibiting collagen-induced aggregation in PRP (p ≤ 0.0001). ASA alone and clopidogrel + ASA were significantly more effective than dipyridamole + ASA in inhibiting arachidonic acid-induced platelet aggregation in whole blood (p ≤ 0.0001). Conclusions: Based on ex vivo platelet aggregometry, clopidogrel + ASA is a more potent antiplatelet regimen than either ASA alone or the marketed combination of dipyridamole + ASA. However, the clinical significance of this finding remains to be confirmed.

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