High cholesterol hinders the effectiveness of aspirin

November 13, 2000

Findings from a University of Maryland study presented at a national meeting

A daily dose of aspirin reduces the risk of a heart attack in 75 percent of people with heart disease, but in about 25 percent of patients using it, aspirin offers no protection. Researchers at the University of Maryland Medical Center in Baltimore now think they know why some of the people who take aspirin are not protected. Their study, presented at the 73rd Scientific Sessions of the American Heart Association in New Orleans on November 14, shows that in those patients, high cholesterol is hindering the effectiveness of the aspirin.

Aspirin, which reduces the clumping or aggregation of blood platelets, has been proven to reduce the risk of a heart attack by 20 to 30 percent, when taken daily. However, in the University of Maryland study, 60 percent of patients with cholesterol levels above 220 mg/dL still had platelet aggregation, in spite of daily aspirin doses, putting them at increased risk of a heart attack.

"We know that aspirin protects against heart disease," says Michael Miller, M.D., F.A.C.C., director of the Center for Preventive Cardiology at the University of Maryland Medical Center and associate professor of Medicine at the University of Maryland School of Medicine. "So we prescribe aspirin for our patients, but we don't measure the effectiveness. This study shows that aspirin may not always work, especially in people with high cholesterol. These people remain at increased risk."

For the study, blood samples from 63 heart disease patients who had been taking 325 mg of aspirin daily for at least thirty days, were tested to see whether the blood platelets clumped together when a special agent was introduced. The test showed that aspirin prevented clumping in 41 patients but in 20 others there was no response. Of the patients with high cholesterol (above 220mg.dL), 60 percent were not helped by the aspirin, compared to 20 percent of patients with cholesterol lower than 180 mg/dL in whom aspirin did not have an impact.

"While previous studies have linked high cholesterol with increased platelet aggregation, this is the first study to look at platelet responsiveness in aspirin users," says Maribeth Friend, MS, MT, a visiting professor at the University of Maryland School of Medicine working with Dr. Miller. Friend presented the study results.

"Other strategies need to be considered for patients with high cholesterol who are not responding to aspirin," says Dr. Miller. "Perhaps a larger dose of aspirin needs to be recommended or other more aggressive efforts undertaken to reduce the total cholesterol."

Friend says the test used in the study could one day be a tool for doctors to evaluate whether the aspirin is helping.

Ivana Vucenik, Ph.D. was also co-author of the study.
Barbara Crawford (bcrawford@umm.edu)
Ellen Beth Levitt (eblevitt@umm.edu)
Gwen Newman (gnewman@umm.edu)

University of Maryland Medical Center

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