Hello, everyone. I'm Dr Kenny Lin, a family physician at Georgetown University Medical Center in Washington, DC, and I blog at Common Sense Family Doctor.
In a previous Medscape commentary, I discussed the 2016 US Preventive Services Task Force (USPSTF) guideline on using low-dose aspirin for primary prevention of cardiovascular disease and colorectal cancer. At that time, the USPSTF recommended that adults in their 50s start taking low-dose aspirin if they have a 10% or greater 10-year cardiovascular event risk, do not have bleeding risk factors, and are willing to take aspirin for at least 10 years. Supporting evidence included a systematic review of 11 randomized controlled trials of aspirin with myocardial infarction (MI) and stroke outcomes published between 1988 and 2014, as well as a complementary review of episodes of major gastrointestinal (GI) bleeding and hemorrhagic strokes that occurred in trial participants. As then–Task Force member Douglas Owens explained in a commentary published in American Family Physician, their goal was to select adults at high-enough cardiovascular risk that their expected benefit from aspirin would outweigh the harms of bleeding complications.
This guideline left some questions for family physicians. Nine of the 11 aspirin trials analyzed by the Task Force are now more than 10 years old, performed when more people smoked, fewer took statins, and high blood pressure was treated less intensively than it is today. Is it possible that the benefits seen in these older studies do not apply to contemporary primary care patients? Also, the USPSTF's systematic review suggested that aspirin's effects did not change in persons with diabetes, but only three trials specifically recruited these patients. It wasn't very long ago that most experts considered diabetes to be a "coronary artery disease risk equivalent." So, might aspirin actually benefit a broader age range of patients with diabetes—for example, starting at age 40?
Two new trials whose results were presented at the European Society of Cardiology's 2018 Congress and simultaneously published in the Lancet and the New England Journal of Medicine provided new data to answer these questions. In the Aspirin to Reduce Risk of Initial Vascular Events (ARRIVE) trial, men aged 55 or older and women aged 60 or older without diabetes were recruited from primary care settings in six European countries and the United States, and randomized to 100 mg of enteric-coated aspirin or placebo once daily for a median follow-up of 5 years. Originally meant to test the cardiovascular benefits of aspirin in a moderate-risk population, ARRIVE turned out to be a trial of lower risk instead, as less than 5% of participants had a cardiovascular event during the study. There was no difference between the groups in a composite outcome of cardiovascular death, MI, unstable angina, stroke, or transient ischemic attack. However, 1% of the aspirin group experienced GI bleeding compared with only 0.5% of the placebo group.
The A Study of Cardiovascular Events in Diabetes (ASCEND) trial mirrored the aspirin-placebo comparison in the ARRIVE trial in adults with diabetes aged 40 or older in UK primary care practices. After a mean follow-up of 7.4 years, a statistically significantly lower percentage of the aspirin group had experienced serious vascular events than the placebo group, offset by an increased percentage of major bleeding events. The authors calculated a number needed to treat of 91 to prevent a vascular event, and a number needed to harm of 112 to cause a major bleeding event, for little to no net benefit.
Although neither ARRIVE nor ASCEND was designed to evaluate the effects of aspirin on colorectal cancer (which previous studies found may take a decade or more for benefits to appear), they should prompt the USPSTF to re-evaluate their 2016 guideline soon. These trials' negative results are convincing enough for me to restrict aspirin for primary prevention to patients at very high cardiovascular risk—20% or more over 10 years—or to those at moderate risk who are unable to tolerate statins.
In terms of treatment priorities for family physicians: Support smoking cessation and lifestyle changes, control high blood pressure, prescribe a statin, and only then consider aspirin.
This has been Dr Kenny Lin for Medscape Family Medicine. Thank you for listening.
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Cite this: The Latest Aspirin Research: Implications for Primary Care - Medscape - Sep 25, 2018.