Aspirin Update

By Peter J. Rice, PharmD, PhD, BCPS, FAPhA ~

There are drugs in use today which are older than aspirin, but not very many. Part of the reason that aspirin is still around is that its use has continued to evolve over the years. But recently the benefits and risks of aspirin have been re-evaluated resulting in revised recommendations for patients.

Aspirin was initially made from an ingredient isolated from the bark of the willow tree and patented in 1899 by the Bayer company as a drug for pain and fever. Aspirin was the predominant non-opioid pain reliever for the first half of the 20th century. The 1950s brought competition from Tylenol™ (acetaminophen), a drug which shares activity for pain and fever. Acetaminophen lacks anti-inflammatory activity, and aspirin remained a preferred drug for inflammation until the development of ibuprofen and other non-steroidal anti-inflammatory drugs, or NSAIDs. Aspirin might have been lost in the 1980s when its use was associated with Reye Syndrome in children, but the discovery of its effect on platelet aggregation advanced its use to inhibit blood clotting and prevent heart attacks and strokes.

All drugs produce effects that are beneficial to patients and effects that pose a risk to patients. Aspirin inhibits platelet aggregation, which can help prevent heart attacks and stroke caused by clotting, but which can also lead to gastrointestinal bleeding which can be life threatening in some patients. Many patients with significant cardiovascular risk take between 81 and 325 mg of aspirin each day to protect against inopportune blood clotting.

Two papers published this summer in the medical journal Lancet have examined how aspirin is used most commonly to prevent cardiovascular events.

In a paper published in July, Peter Rothwell and colleagues examined the effect of aspirin on cardiovascular risk and colorectal cancer in patients of varying bodyweight. A daily baby aspirin (81mg) was found to provide some cardiovascular protection in patients weighing up to about 150 lb. Adult strength aspirin (325mg) was found to provide some cardiovascular protection to patients weighing more than 154 lb. Aspirin also helped protect against colorectal cancer. The risks or harms of aspirin therapy were also dependent on weight, with smaller patients – and women are generally smaller than men – at increased risk for inopportune bleeding and death.

In a paper published in August, Michael Gaziano and colleagues re-examined the role of aspirin in men 55 and older and in women 60 and older at moderate risk for cardiovascular events. Patients receiving aspirin in the study showed no improvement in the incidence of cardiovascular disease or death. Patients receiving aspirin did have an increase in the incidence of bleeding. This was surprising because aspirin treatment typically decreases cardiovascular incidents, but in this study the frequency of cardiovascular was lower than expected. The authors propose that – because of advances in medical prevention and treatment – patients are now at lower risk for cardiovascular disease and stroke.

What does this mean for you? These results suggest that patients and healthcare providers should consider the benefits and risks of aspirin therapy and adjust their daily aspirin dosage based on patient weight. The current benefits of preventive aspirin may be over-rated and patients may want to be at higher risk before commencing aspirin. If you are taking aspirin, consider a baby aspirin (81mg) if you weigh less than 150 lb, and a half-strength (180mg) or regular strength (325mg) aspirin if you weigh more than 150 lb. The incidence of bleeding for those on aspirin therapy increases with age, from around 4 per 1000 patients for women under 60 years of age up to 36 per 1000 patients for men over 70 years old.

Current recommendations from the US Preventive Services Task Force (link below) have not yet incorporated this new data. Talk with your prescriber or pharmacist to help you decide if you should take an aspirin a day, and which dose is most appropriate. Take good care of yourself.


U.S. Preventive Services Task Force Final Recommendation Statement
Aspirin Use to Prevent Cardiovascular Disease and Colorectal Cancer: Preventive Medication (September 2017)

Rothwell-PM et al: Effects of aspirin on risks of vascular events and cancer according to bodyweight and dose: analysis of individual patient data from randomised trials.
Lancet 2018 Aug 4; 392(10145): 387–399

Gaziano-JM et al: Use of aspirin to reduce risk of initial vascular events in patients at moderate risk of cardiovascular disease (ARRIVE): a randomised, double-blind, placebo-controlled trial.
Lancet. 2018 Sep 22;392(10152):1036-1046.

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