Effect of different aspirin doses on platelet aggregation in patients with stable coronary artery disease

Abstract Background:  Aspirin is widely used as an antiplatelet agent in the primary and secondary prevention of cardio­vascular disease. In order to spare prostacyclin formation and reduce gastrointestinal side-effects, very low doses of aspirin have been introduced. However, it remains unclear whether these low doses are equally effective with respect to inhibition of platelet aggregation. Aims:  In a randomized, controlled study in 60 patients with stable coronary artery disease, the effects on platelet aggregation of five doses (50, 80, 100, 162.5 and 325 mg) of aspirin, which are widely used in clinical practice, given for 70 days, were investigated. Two ­reagents, adenosine diphosphate (ADP) and epinephrine, were used to induce platelet aggregation in ­platelet-rich plasma. An age- and sex-matched group of people without coronary artery disease served as the control. Results:  ADP- and epinephrine-induced platelet ­aggregation was 78.2 ± 12.8% and 76.7 ± 15.5% of maximum aggregation in the control group. Aspirin inhibited platelet aggregation in a dose-dependent manner. Minimum platelet aggregation was observed at a dose of 325 mg aspirin (27.5 ± 17.4% with ADP). Doses of 50 and 80 mg aspirin were much less effective in inhibiting platelet aggregation (59.1 ± 11.4% and 50.3 ± 12.1% with ADP, respectively). Doses of 100 and 162.5 mg aspirin produced significantly greater inhibition of platelet aggregation than lower doses (36.2 ± 11.7% and 38.5 ± 19.8% platelet aggregation with ADP, respectively). Conclusion:  Our results demonstrate that doses of aspirin less than 100 mg are not as effective at inhibiting platelet aggregation as doses greater than 100 mg. (Intern Med J 2003; 33: 350−354)