Among long-term users, discontinuation of low-dose aspirin in the absence of major surgery or bleeding was associated with more than a 30 percent increased risk of cardiovascular events, according to a study published Sept. 25 in Circulation.

In a large nationwide patient cohort study, Johan Sundström, MD, PhD, et al., assessed 601,527 users of low-dose aspirin for primary or secondary prevention in the Swedish prescription register between 2005 and 2009. Users were over 40 years old, free from previous cancer and had 80 percent or more adherence during the first observed year of treatment. The first three months after a major bleeding or surgical procedure were excluded from the time at risk.

During a median follow-up of 3.0 years, results showed that 62,690 cardiovascular events occurred. Patients who discontinued aspirin had a higher rate of cardiovascular events than those who continued (multivariable-adjusted hazard ratio, 1.37; 95 percent confidence interval, 1.34-1.41), consistent with an additional cardiovascular event observed per year in one of every 74 patients who discontinue aspirin. The risk appeared to increase as soon as patients discontinued aspirin, with no safe interval.

Subgroup analyses showed patients who were older and had prior cardiovascular disease were at higher risk for cardiovascular events when off aspirin, whereas treatment with oral anticoagulant or other antiplatelet drugs was associated with lower risk increase for cardiovascular events when off aspirin.

Aspirin discontinuation was found to be particularly dangerous among patients with previous cardiovascular disease. An additional cardiovascular event per year occurred in every one of 36 secondary prevention patients who discontinued aspirin compared with an additional cardiovascular event per year in every one of 146 primary prevention patients who discontinued aspirin.

"Strengths include the large contemporary sample rendering >60,000 cardiovascular events, universal coverage of the prescription register and hence inclusion of all long-term low-dose aspirin users nationwide, the universal coverage of the high-precision registers for determining the outcomes, and minimal loss to follow-up," the study authors write.

Keywords: Aspirin, Platelet Aggregation Inhibitors, Secondary Prevention, Cardiovascular Diseases, Confidence Intervals, Universal Health Insurance, Follow-Up Studies, Sweden, Risk Factors, Primary Prevention, Hemorrhage, Anticoagulants, Neoplasms

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