Platelet response to aspirin 50 and 100 mg in patients with coronary heart disease over a five-year period.

Aspirin has been shown to decrease cardiovascular (CV) events by ∼25%. Despite aspirin therapy 10% to 20% of patients with arterial vascular disease develop atherothrombotic events. A meta-analysis of antiplatelet therapy showed a progressive decrease in clinical efficacy of aspirin after 2 years. Whether this is due to a decreased sensitivity to aspirin during long-term therapy remains unclear. A prospective randomized clinical trial with serial monitoring over 5 years was conducted in 100 patients with documented coronary heart disease. We investigated whether long-term treatment with aspirin 50 and 100 mg affects platelet response similarly. Occurrence of CV events was documented. Platelet sensitivity to aspirin, prostacyclin, and adenosine diphosphate-, collagen-, and epinephrine-induced platelet aggregation were evaluated over time. In addition, β-thromboglobulin and inflammatory markers were measured. Four patients were lost to follow-up and 10 patients died. Eleven patients developed nonfatal CV events. In the 2 groups platelet response to aspirin and the referenced variables remained unchanged over 5 years. In patients who developed CV events, the last monitoring interval revealed no difference in platelet response to aspirin. However, patients with nonfatal and fatal CV events showed increased inflammatory markers versus patients without CV events independent of aspirin 50 or 100 mg intake. In conclusion, our study revealed no difference in antiplatelet response to aspirin 50 versus 100 mg or CV events over 5 years in patients with coronary heart disease.