Aspirin Prescribing Guidelines
With help from Dr. Andy Coyle & Dr. Michael Herscher
Primary Prevention: NO
As per USPSTF, Now Grade B for adults 50-59yo with 10-year ASCVD risk > 10%. USPSTF is currently re-evaluating their statement, and likely to downgrade to Grade C (patient-specific).
1) 2012 Meta-Analysis: [Link] (https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/1108721). 20% relative risk reduction of non-fatal myocardial infarction (MI) at 10 years in patients on aspirin for primary prevention, but absolute risk reduction is around 0.3%, with a number needed to treat of ~ 300. Number need to harm for non-fatal bleed ~300.
2) ASPREE: [Link] (https://www.nejm.org/doi/full/10.1056/nejmoa1803955). Healthy adults 65+ yo randomized to aspirin or placebo. Increased risk of mortality in the low-dose (81mg) aspirin group, mostly driven by cancer-related deaths. Failed to show benefit of aspirin in this group for primary prophylaxis for cardiac events.
3) ARRIVE: [Link] (https://www.thelancet.com/article/S0140-6736(18)31924-X/fulltext). No benefit of aspirin for primary prophylaxis in older, moderate risk individuals.
4) ASCEND: [Link] (https://www.nejm.org/doi/full/10.1056/NEJMoa1804988?query=main_nav_lg). Patients with diabetes do show some effect from low-dose aspirin for primary prevention, but effect size small with 12% relative risk reduction of risk of first vascular event. ~ 1% absolute risk reduction, number needed to treat ~ 100. So would need to treat 100 people for around 10 years to prevent one non-fatal vascular event (usually preventing a heart attack). BUT increase in bleeding risk. Separated study population into low (< 5% risk), intermediate (5-10% ASCVD risk), and high (> 10% ASCVD risk) and found that the benefit of aspirin over placebo did increase from low to higher risk populations, BUT the bleeding risk also went up. The higher the vascular risk, the higher the risk of bleeding events (and higher the risk of fatal bleeding events). Overall, the benefits and risks of aspirin as so close in magnitude that we can't really uniformly recommend to any population.
5) Systematic Review and Meta-Analysis (JAMA 2019). Includes ASCEND and ASPREE. [A Link] (https://jamanetwork.com/journals/jama/fullarticle/2721178).
In participants with low cardiovascular risk: 0.34% absolute risk reduction of composite of cardiac events with aspirin prophylaxis, 0.40 absolute increase in risk of major bleeding with aspirin prophylaxis, no change in overall mortality. In participants with high cardiovascular risk: 0.63% absolute risk reduction of composite of cardiac events with aspirin prophylaxis, 0.64% absolute increase in risk of major bleeding with aspirin prophylaxis, no change in overall mortality.
If you have a patient 50-59yo with no history of cardio- or cerebro-vascular events that for some reason you particularly think is high-risk for vascular events but uniquely low-risk for bleeding, then you can consider aspirin primary prophylaxis.
Secondary Prevention: YES
Important to remember that low-dose (81mg) daily Aspirin for SECONDARY prevention is incredibly effective so have to be cautious not to remove it from people with any history of vascular disease (AAA, TIA, stroke, MI, PVD, etc).