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Aspirin May Not Prevent Stroke

Katherine M. Bennett

While daily doses of aspirin reduce the risk of myocardial infarction, this regimen does not necessarily reduce the risk of
stroke in patients without vascular disease, researchers concluded.

The benefits of aspirin in reducing the risk for myocardial infarction and stroke in patients with vascular disease are well known. But, an estimated 8 million elderly Americans without vascular disease regularly take aspirin to prevent strokes without clear evidence that it works.

In the March issue of Archives of Neurology, Robert G. Hart, M.D., and fellow researchers released the results of a meta-analysis examining the effect of aspirin on the primary prevention of stroke and other major vascular events. The researchers combined data from five randomized trials of primary prevention involving 52,251 patients, with a mean age of 57 years, followed for an average of 4.6 years.

Three trials involved high-risk patients, and two trials involved healthy male physicians. Aspirin dosages ranged from 75 to 650 mg daily.

Meta-analysis showed that aspirin consumption does not significantly affect the occurrence of stroke, despite a 26 percent decrease in the occurrence of myocardial infarction in people without vascular disease. Aspirin's lack of
reduction of stroke in low-risk patients contrasts significantly with another meta-analysis's finding of a protective effect in patients with vascular disease.

Aspirin use by patients at low risk for stroke has negative consequences as well. According to the recent study, the occurrence of intracranial hemorrhage increases by about 35 percent with the regular use of aspirin. Previous clinical trials testing aspirin dosages of 75 mg daily to 325 mg every other day have shown an average 50 percent increase in the occurrence of major extracranial bleeding.

The researchers declared the benefits of regular aspirin use by healthy older adults to prevent vascular events "insufficient to warrant a general recommendation for widespread use".

In the same issue of Archives, H. J. M. Barnett, M.D., and Michael Eliasziw, Ph.D., of The John P. Roberts Research Institute in Canada, commented on the meta-analysis, agreeing that the researchers made credible conclusions. However, Barnett and Eliasziw questioned whether the findings justify the researchers' dismissing aspirin as a therapeutic tool in primary stroke prevention.

Barnett and Eliasziw noted that all of the healthy people in the meta-analysis were men at ages when men most commonly have a myocardial infarction, not a stroke. A trial involving men and women at least 10 to 15 years older than the mean age of people in the meta-analysis's trials would provide more convincing evidence for a negative benefit with
widespread aspirin use.

For clinicians still convinced that regular aspirin use by healthy people can prevent stroke, the appropriate dosage remains debatable. Hart and colleagues suggest 75 to 81 mg daily, on the basis of available data. However, Barnett and Eliasziw present both sides of the aspirin-dose controversy and contend that "the optimal dose of aspirin for any stoke-preventing strategy remains unknown."

To read the article and editorial, go to (PDF) and (PDF).