Effect of increasing doses of aspirin on platelet aggregation among stroke patients

BACKGROUND AND PURPOSE: Aspirin has been shown to reduce the risk of myocardial infarction and stroke. Some investigators believe that low-dose aspirin inhibits platelet aggregation to the same degree as high-dose aspirin. Our study aimed to assess the effect of increasing doses of aspirin on the degree of platelet aggregation induced by collagen and adenosine diphosphate (ADP) among stroke patients. METHODS: Sixteen poststroke patients were prescribed aspirin at daily doses of 40, 80, 160, 325, 650, and 1,300 mg, each dose to be taken for 14 days (total duration 12 weeks). Platelet aggregation studies using 2 microgram/ml collagen and 2 microM ADP were performed on platelet-rich plasma at baseline and on the 14th day of each dose. RESULTS: Platelet aggregation studies using 2 microgram/ml collagen at the start of treatment and at the 14th day of each dose revealed dose-dependent inhibition by aspirin starting at 40 mg/day, but was optimal at 80- 160 mg/day. ADP-induced platelet aggregation inhibition appears to be dose dependent up to 1,300 mg/day. CONCLUSION: Inhibition of collagen-induced platelet aggregation by aspirin appears to be optimal at 80-160 mg/day, while ADP-induced platelet aggregation inhibition by aspirin appears to be dose dependent up to 1,300 mg/day in our poststroke patients, albeit to a less remarkable degree at higher doses.