In 1948, an internist from California noticed a dramatically low occurrence of myocardial infarction (MI) among hundreds of his male patients who used aspirin, leading him to recommend daily aspirin use to his patients and colleagues1. Since then, clinical trials and treatment guidelines have helped to clarify the benefits of and candidates for daily low-dose aspirin (i.e., aspirin 75162.5 mg daily). The ASHP Therapeutic Position Statement on the Daily Use of Aspirin for Prevention of Cardiovascular Events that appears in this issue of AJHP provides a concise and practical overview of relevant key literature and current guidelines.
There is confusion among prescribers about how to identify appropriate candidates for daily low-dose aspirin, particularly for the primary prevention of cardiovascular events, and the magnitude of bleeding risk associated with low-dose aspirin. To help determine whether the benefits of daily low-dose aspirin outweigh the risks, individuals should undergo a simple 10-year Framingham coronary heart disease (CHD) risk assessment. A 10% risk of CHD over the next 10 years warrants the use of low-dose daily aspirin, provided that the patient does not have major risk factors for gastrointestinal (GI) or cerebral bleeding. In addition, data and guidelines support considering aspirin therapy for patients with a 610% 10-year CHD risk. The risk of aspirin-induced bleeding usually outweighs the benefit of reducing cardiovascular events when the 10-year CHD risk is less than 6%.
The results of the Women’s Health Study (WHS) demonstrate that relying on 10-year CHD risk predictions may not provide sufficient guidance for the use of daily low-dose aspirin in women for primary cardiovascular event prevention.5 This large, randomized, placebo-controlled trial included nearly 40,000 women 45 years of age or older who received either low-dose aspirin or placebo. The majority of participants (84%) had a 10-year CHD risk below 5%. The primary endpoint was a first cardiovascular event, defined as nonfatal MI, nonfatal stroke, or death from cardiovascular causes. After 10 years of follow-up, no significant difference in the rate of first cardiovascular events was found between aspirin- and placebo-treated patients. Subgroup analyses revealed that aspirin therapy was associated with significantly fewer stroke events, particularly ischemic and nonfatal stroke, versus placebo. No other significant differences were noted. Women treated with aspirin had significantly more GI bleeding and peptic ulcers. When stratified by baseline characteristics, it appeared that women 65 years of age benefited most from aspirin therapy (i.e., significantly lower rate of first cardiovascular events and a marginally significant reduction in is-chemic stroke). Of importance, women 65 years of age represented a small portion of the study population but accounted for nearly one third of all cardiovascular events.
The results of this study verified that women suffer from stroke more often than MI than do men. Therefore, the ability of daily low-dose aspirin therapy to lower the risk of stroke has major clinical significance. In the WHS, the risk of stroke was reduced without reducing the risk of MI or death from all cardiovascular causes combined.
Health care professionals should develop methods within their health systems for identifying patients who may benefit from low-dose aspirin therapy and ensure that this therapy is initiated. No other medication is as cost-effective as aspirin for preventing cardiovascular events. However, it must be understood that low-dose aspirin is not completely harmless, as "low-dose" may imply.