Aspirin resistance: a new independent predictor of vascular events?

Aspirin is an effective antiplatelet agent for preventing important clinical complications of atherothrombosis (1). Among 29,652 high-vascular-risk patients randomly allocated to long-term aspirin therapy, the rate of serious vascular events (nonfatal myocardial infarction, nonfatal stroke, or vascular death) after about two years was 12.9%, compared with 16.0% among 29,743 patients allocated to control (1). This is an odds reduction of 23% (standard deviation 2), a relative risk reduction of 19%, and an absolute risk reduction of 3.1% over two years, or 1.5% per year (1). Therefore, aspirin fails to prevent more than four-fifths (81%) of recurrent serious vascular events among high-risk patients, and one in eight high-risk patients (12.9%) experiences a recurrent vascular event in the next two years despite taking aspirin.