Aspirin for primary prevention should be better targeted, new study and FDA say

A recently published study and announcement from the FDA caution against wide use of aspirin for primary prevention of cardiovascular events.

The study evaluated coronary artery calcium (CAC) scoring as a method to determine which patients should take aspirin for primary prevention. Findings were based on more than 4,000 participants in the Multi-Ethnic Study of Atherosclerosis who were not on aspirin at baseline and were free of diabetes. Median follow-up was 7.6 years, and researchers calculated 5-year number needed to treat (NNT) and number need to harm (NNH) rates using an assumption that aspirin reduced event rates by 18% and increased major bleeding by 0.23%. Results were published online by Circulation: Cardiovascular Quality and Outcomes on May 6.

Study patients were stratified according to Framingham Risk Score (FRS) calculations of their risk of developing coronary heart disease in the next 10 years. Participants who had a CAC score of 100 or higher were found to benefit from aspirin, regardless of their FRS risk status. The NNT was 173 for patients with FRS <10% and 92 for those with FRS ≥10%. The NNH was 442 for all patients.

Patients who had a zero CAC score did not benefit from aspirin overall (NNT for <10%, 2,036; NNT for ≥10%, 808). However, researchers noted that women with elevated coronary risk according to traditional factors received a net benefit from aspirin.

About a quarter of the patients fell between the 2 categories, with a CAC of 1 to 99, and the study could not calculate definitive risk/benefit profiles for them. Patient preference should take a greater role in their treatment plans, the authors suggested. For many of the other patients, CAC score could change treatment recommendations regarding aspirin, the authors said. More than 10% of participants who don't qualify for aspirin under current American Heart Association guidelines had a CAC score ≥100, while over 30% of the participants who would be on aspirin were found to have a zero CAC score.

Cost and other effects of CAC testing (radiation, downstream testing, and psychological/behavioral effects) could pose issues with targeting aspirin in this way, the researchers noted, so the study results should be considered hypothesis-generating.

The FDA also recently took a position on use of aspirin for primary prevention. After denying a manufacturer request to change prescribing information to allow marketing of aspirin for prevention of heart attacks in patients with no history of cardiovascular disease, the agency announced to consumers that it “does not believe the evidence supports the general use of aspirin for primary prevention of a heart attack or stroke.”

Evidence does support use in patients who have already had a heart attack or stroke or who have other evidence of coronary artery disease, such as angina or a history of a coronary bypass operation or coronary angioplasty, the agency said. However, additional clinical trials are underway that could provide new evidence for changing the indications for aspirin, according to the statement.