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Patients with a history of cardiovascular disease who discontinue prophylactic therapy with low-dose aspirin are at an increased risk of adverse cardiovascular events, compared with patients who continue with the drug. “Our study is the first to report an increased risk of cardiovascular events after low-dose aspirin discontinuation in the [primary care] setting,” says Dr Luis García Rodríguez, from the Spanish Center for Pharmacoepidemiologic Research.

The investigators identified 39,513 individuals (aged 50–84 years) who had received a first prescription of aspirin (75–300 mg per day) for secondary prevention of cardiovascular outcomes. In a nested case-control analysis, the risk of myocardial infarction or death from cardiac causes was calculated in patients who discontinued aspirin therapy and compared with those who remained on the drug during follow-up (mean 3.2 years).

Compared with ongoing users, people who stopped taking low-dose aspirin had a significant increase in the risk of nonfatal myocardial infarction (rate ratio 1.63, 95% CI 1.23–2.14), and the combined risk of nonfatal myocardial infarction or death from coronary artery disease (rate ratio 1.43, 95% CI 1.12–1.84), regardless of previous duration of adherence to antiplatelet therapy. These increased risks are of approximately the same magnitude as the beneficial effect of prophylactic antiplatelet therapy on nonfatal cardiovascular events. “This reversion to baseline risk is most likely the result of the recovery of thromboxane A2 generation and platelet function after aspirin discontinuation, [which] might have a role in both vascular occlusion and vasoconstriction,” suggests Dr García Rodríguez.

Aspirin discontinuation was primarily a result of patient nonadherence, but the second most-commonly cited cause was safety concerns regarding upper gastrointestinal ulcers and bleeding. However, the reduction in the risk of major coronary events outweighs the risk of major bleeding, particularly in patients at high risk of cardiovascular events. Schemes to improve patient adherence and reduce aspirin discontinuation (which has been reported to be as high as 50%) could, therefore, be highly cost-effective, given the major health benefits and the relatively low cost of the drug.