Aspirin Prophylaxis

A study published recently (March 31, 2014) in The New England Journal of Medicine found that patients who took daily aspirin (200 mg initially, then 100 mg) just before noncardiac surgery and continued it for 30 days (or 7 days before going back to a regular aspirin regimen) had a higher risk of major bleeding than patients who took a placebo, and no beneficial effect on cardiovascular events.

Aspirin prophylaxis reduces the incidence of myocardial infarction and death in patients with coronary events or ischemic stroke, and in those undergoing angioplasty or a coronary artery bypass graft. Aspirin can also prevent myocardial infarction in asymptomatic men and ischemic stroke in asymptomatic women, but the risk-benefit ratio is less favorable because the thrombotic risk is lower and the benefit in preventing thrombosis is offset by a small increased risk of hemorrhagic stroke.

Bayer Laboratories have been producing aspirin since 1899, but it took 50 years for anyone to realize that aspirin could cause bleeding. According to Wikipedia:

“Aspirin’s effects on blood clotting (as an antiplatelet agent) were first noticed in 1950 by Lawrence Craven. Craven, a family doctor in California, had been directing tonsillectomy patients to chew Aspergum, an aspirin-laced chewing gum. He found that an unusual number of patients had to be hospitalized for severe bleeding, and that those patients had been using very high amounts of Aspergum. Craven began recommending daily aspirin to all his patients, and claimed that the patients who followed the aspirin regimen (about 8,000 people) had no signs of thrombosis. However, Craven’s studies were not taken seriously by the medical community, because he had not done a placebo-controlled study and had published only in obscure journals.”

It took decades more before aspirin became established as a prophylactic antithrombotic agent. And we still have a lot to learn about this old, old drug. For instance, many of us prescribe a daily 325-mg aspirin tablet for cardiovascular prophylaxis, but a daily dose of 75 mg achieves complete inactivation of platelet COX-1 (the mechanism of the drug’s antiplatelet effect), and higher doses are more likely to inhibit prostacyclin and cause gastrointestinal bleeding.

A soon-to-come issue of The Medical Letter will include a brief article on whether enteric-coated aspirin is less effective than plain aspirin as an antiplatelet agent. And it’s not so easy to find plain aspirin in stores anymore. Just like regular strength acetaminophen. But that’s another story for another day.

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Comments

  1. Herb Kleinman says:

    Hard to understand the researchers’ strategy for using doses of aspirin (100 mg, 200 mg) when these strengths do not seem to be available here. Checking the “How Supplied” section in Micromedex, I found no aspirin products at these doses. What’s the deal?

  2. I have never shopped for aspirin and been unable to find it easily. Writing from Metro Atlanta. I take two 325’s each morning as a prophylactic for general pain I expect will come if I do strenuous activities, which is nearly every day. BTW, my Dollar Trees sell 100 tabs/$1.

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