What are the benefits and risks of daily low-dose aspirin for primary prevention of CV events?
EVIDENCE BASED ANSWER:
One nonfatal myocardial infarction (MI) will be avoided for every 126 to 138 adults who take daily aspirin for 10 years (strength of recommendation [SOR]: A, systematic reviews and meta-analyses of multiple randomized controlled trials [RCTs]).
Taking low-dose aspirin for primary prevention shows no clear mortality benefit. A benefit for primary prevention of stroke is less certain. Although no evidence establishes increased risk of hemorrhagic stroke from daily low-dose aspirin, one gastrointestinal hemorrhage will occur for every 72 to 357 adults who take aspirin for longer than 10 years (SOR: A, systematic reviews and meta-analyses of multiple RCTs and cohort studies).
Aspirin carries risk of GI hemorrhage, but not hemorrhagic stroke
A companion 2016 systematic review of 16 RCTs, cohort studies, and meta-analyses evaluated the risk of serious bleeding in patients using low-dose aspirin for primary prevention of either CVD or cancer.3 The review (number of patients not reported) found that estimated excess bleeding events differed substantially depending on varying sources for baseline bleeding rates in aspirin nonusers.
The most conservative comparison yielded an NNH of 72 over 10 years of therapy (1.39 excess major GI bleeding events per 1000 person-years, 95% CI, 0.70-2.28). Comparison with other baseline bleeding rates in trial data yielded less risk of harm, with an NNH of 357 over 10 years (0.28 excess major GI bleeding events per 1000 person-years; 95% CI, 0.14-0.46). Excess risk for hemorrhagic stroke was not statistically significant (0.32 excess events per 1000 person-years; 95% CI, −0.05 to 0.82).
RECOMMENDATIONS
The US Preventive Services Task Force gives a Grade B recommendation (recommended, based on moderate to substantial benefit) to the use of aspirin to prevent CVD among adults ages 50 to 59 years with an ASCVD risk ≥10% who don’t have increased bleeding risk and are capable of 10 years of pharmacologic adherence with a similar expected longevity.4 The Task Force assigns a Grade C recommendation (individual and professional choice) to patients 60 to 69 years of age with the same constellation of risk factors and health status. Insufficient evidence was available to make recommendations for other age cohorts.
,The American College of Chest Physicians recommends 75 to 100 mg of aspirin daily for adults 50 years or older who have moderate to high CV risk, defined as ≥10%.5
A working group of the European Society of Cardiology (ESC) released a statement in 2014 recommending aspirin for primary prevention in adults with a CV risk ≥20% and no risk factors for bleeding. For patients with a CVD risk between 10% and 20%, the ESC recommends deferring to patient preference.6
