Inhibition of platelet aggregation by aspirin alone and by aspirin in combination with clopidogrel: synergy, incompatibility and additivity

The results of combined anti-platelet therapy for aspirin followed by aspirin plus ticlopidine were previously reported in terms of inhibition of platelet aggregation in patients with history of ischemic stroke. Another anti-platelet agent, considered to be safer and said to have the same platelet inhibitory effects, clopidogrel has now replaced ticlopidine. We sought to study again the effects of combination aspirin-clopidogrel therapy in a different group of patients with ischemic stroke. We wanted to expand our experience with a fuzzy theory solution to the search for synergy, incompatibility and additivity in individual patients taking combination anti-platelet therapy. We evaluated 56 patients receiving combination aspirin-clopidogrel therapy for prevention of recurrent arterial (vascular) occlusion, i.e., prevention of stroke, myocardial infarction and lower extremity ischemia. Platelet aggregation studies were performed ex-vivo on blood drawn from each patient while taking aspirin alone and later while taking aspirin plus clopidogrel. The methodology for performance of platelet aggregation studies has been published elsewhere and in no way deviates from that original protocol