Aspirin, platelets and prevention of vascular disease.

Aspirin inhibits thromboxane and prostaglandin formation in platelets and in vascular cells. It prevents platelet aggregation by irreversible acetylation of cyclooxygenase, a key enzyme in arachidonic acid metabolism. On the basis of its antiplatelet effect, aspirin has been assessed during the past two decades in patients with a history of myocardial infarction, stroke, transient ischemic attack or unstable angina. A meta-analysis of randomized controlled trials of long-term aspirin treatment for the secondary prevention of vascular disease indicated that aspirin (300-1500 mg daily) significantly reduced fatal and non-fatal vascular events. More recently aspirin (160 mg daily) produced a significant reduction in hospital vascular mortality and in non-fatal events in patients with suspected acute myocardial infarction. The combination of aspirin and streptokinase was significantly better than either drug alone. On the other hand, two primary prevention trials of aspirin in healthy doctors did not show any modification of vascular mortality despite an overall reduction of non-fatal myocardial infarction. Resolution of some problems related to the mechanism of action of aspirin and to selection of trial populations will possibly increase the benefit/risk ratio of aspirin treatment for the prevention of vascular disease.