Characterization of the antiplatelet effect of aspirin at enrollment and after 2-year follow-up in a real clinical setting in Japan

Background: Aspirin is an antiplatelet drug widely used for the prevention of cardiovascular diseases. It has been reported that some patients who exhibit a reduced antiplatelet effect of aspirin have higher cardiovascular risk. It is still controversial whether the antiplatelet effect of aspirin diminishes after a few years of treatment. This study aimed to evaluate the antiplatelet effect of aspirin and its 2-year change in Japanese patients. Methods and Results: Collagen-induced platelet-aggregability was measured at enrollment by conventional optical aggregometer in 239 patients undergoing antiplatelet therapy with aspirin alone. Among them, 167 patients were evaluated after 2 years. Whole blood aggregability based on the screen-filtration method was also evaluated. Optical aggregometer studies showed that 27% of patients were low-responders. Multivariate analyses revealed that female sex and non-use of calcium-channel blockers were associated with low responsiveness. The antiplate-let effect of aspirin did not decrease after 2 years. Similar data were obtained with the whole blood aggregometer. Conclusions: In this Japanese patient group, 27% were low-responders to aspirin, and the antiplatelet effect of aspirin did not decrease after a 2-year interval.