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Aspirin Therapy: How Much Is Too Much?

Baby Aspirin Looks to Be the Best Choice for Prevention
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WebMD Health News

Sept. 22, 2003 -- Millions of Americans take an aspirin every day to protect their hearts, but there is still widespread confusion about what's the best dose. Does baby aspirin protect as well as an adult-strength tablet? And is it riskier to take an adult-strength aspirin every day?

A new international study offers some of the best evidence yet that when the risks and benefits of aspirin therapy are weighed, a daily baby aspirin is your best bet.

Researchers compared three different daily aspirin therapy doses and found a similar frequency of heart attacks and strokes among patients taking each of them. But those taking the highest doses -- equivalent to roughly an adult-strength tablet every day -- were at much greater risk for developing bleeding complications. The findings are in the Oct. 7 issue of the American Heart Association (AHA) journal Circulation.

Bigger Isn't Better

"These findings are completely consistent with every other report that has examined aspirin dosage," cardiologist and researcher Ron J.G. Peters, MD, tells WebMD. "There is no indication whatsoever that increasing the dosage improves the outcome of aspirin therapy. But there is a very clear relationship between higher doses and an increased risk for bleeding."

AHA spokesman Sidney C. Smith, MD, agrees that the studies to date suggest that low-dose aspirin therapy is just as effective as higher-dose treatment and probably safer. But he adds that there remains a need for a large-scale, definitive study to answer the question once and for all and to address the role of aspirin therapy in the 15% to 20% of patients who appear to be resistant to its beneficial heart effects.

The newly reported study was actually designed to assess the value of adding the anti-blood clotting drug Plavix to different doses of aspirin therapy in patients with unstable angina. Slightly more than 12,500 patients were randomly selected to receive the drug and aspirin doses ranging from 75 mg to 325 mg daily. The typical baby aspirin is 81 mg, and an adult tablet is 325 mg.

In an earlier report, the combination treatment was found to be superior to aspirin alone, regardless of the aspirin dose given.

In this new study, higher doses of aspirin were no more effective than low-dose aspirin therapy at preventing heart attacks and strokes. But the risk of major and potentially life-threatening bleeding events was much greater among patients on the highest aspirin doses.

Just under 2% of the patients given low-dose aspirin alone experienced life-threatening bleeding events, compared with close to 4% of patients taking more than 200 mg of aspirin a day. Among patients taking aspirin and Plavix, 3% of patients in the low-dose aspirin groups experienced serious bleeding vs. 5% of those in the high-dose aspirin group.

New Aspirin Therapy Guidelines

The researchers conclude that the optimal daily dose of aspirin therapy is between 75 mg and 100 mg a day. Smith says the AHA recommends 75 mg to 325 mg daily for people with a history of heart attack, unstable angina, or blood clot-related strokes.

Those guidelines are being revised, though, and new recommendations are expected early next year. Although Smith did not wish to speculate on whether the recommended dose would be lowered, he did say that he now recommends a daily baby aspirin to his patients.

"This is not a black-and-white issue, but for the majority of patients the accumulating body of evidence suggests that a baby aspirin is all that is needed," he says. "But it would be nice to have large studies that focus specifically on which dose of aspirin is best."

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