Patients who discontinue low-dose aspirin as part of primary or secondary prevention may have a nearly 40% increased risk of cardiovascular events compared to those who continue taking the drug, a recent study found.
Using a Swedish prescription registry, researchers examined a cohort of 601,527 users of low-dose aspirin for primary or secondary prevention between 2005 and 2009. Participants were older than age 40, were free from previous cancer, and had 80% or greater adherence in the first year of treatment during this time. Researchers used inpatient and cause-of-death registers to identify cardiovascular events, excluding the first three months after a major bleeding episode or surgical procedure. Results of the trial, which was partly funded by industry, were published online on Sept. 25 by Circulation.
Overall, 62,690 cardiovascular events occurred during a median follow-up of three years. Patients who continued aspirin had a 4.1% yearly incidence of cardiovascular events, compared to 5.4% among those who stopped taking the drug, and the difference was significant after adjustment (adjusted hazard ratio, 1.37; 95% CI, 1.34 to 1.41). The risk increased shortly after aspirin discontinuation and appeared to persist over time.
The risk of discontinuation corresponded to one additional cardiovascular event for every 74 patients who stopped taking aspirin in a year. This risk was greater among users for secondary prevention (one of every 36 patients) than among users for primary prevention (one of every 146 patients).
The authors noted limitations to the study, such as its observational design and the risk of confounding due to lack of data on socioeconomic status, physical findings (e.g., blood pressure, lipids), and lifestyle measures, including smoking status. They also noted imprecision in determining exposure to aspirin. “These findings can help policymakers focus on simple measures to ensure treatment persistence with a cheap medication like aspirin with substantial public health gains,” they wrote.