VANCOUVER, BRITISH COLUMBIA—Almost half of patients suffering a stroke or transient ischemic attack (TIA) after using daily aspirin therapy showed “aspirin resistance,” a condition in which aspirin does not have the antiplatelet effect needed to prevent a stroke or TIA, researchers reported at the Fifth World Stroke Congress. They also noted that aspirin resistance was significantly higher among patients using “baby” (81 mg) or enteric coated aspirin.

“We know from other research that most patients using low-dose or coated aspirin don’t get an adequate antiplatelet effect,” Mark Alberts, MD, told Neurology Reviews. “In this study we have shown that this aspirin resistance correlates to clinical events. We found that many patients who use daily aspirin therapy are still having strokes or TIAs.”

Dr. Alberts, Professor of Neurology at Northwestern University Medical School and Director of the Stroke Program at Northwestern Memorial Hospital, both in Chicago, and colleagues at Northwestern Memorial collected and studied data on 59 subjects who were treated at the hospital for a stroke or TIA. Patients who had been taking aspirin at least three days prior to admission were designated as chronic aspirin users and were eligible for the study. Most of the subjects (63%) were taking 325-mg daily adult aspirin, while 37% were taking 81-mg daily baby aspirin.

A LACK OF EFFECT

The researchers found that overall, 47% of patients using aspirin showed no antiplatelet effect. Of the 22 subjects using daily baby aspirin, 73% showed no antiplatelet effect, and of the 37 subjects using daily adult aspirin, 32% showed no antiplatelet effect. Specific aspirin-formulation (coated or noncoated) information was available for 29 subjects. The investigators found that of 18 subjects taking coated aspirin, 73% showed no antiplatelet effect. Of the 11 subjects taking uncoated aspirin, 39% showed no antiplatelet effect.

“The importance of this study is that it gets us closer to learning how to maximize the effectiveness of aspirin and to design aspirin treatment to maximize its anticlotting effects,” said Dr. Alberts. “The results of this study also suggest that therapeutic effectiveness might require regular testing of antiplatelet effects for each patient.”

“However,” he added, “the results of this trial also send another clear message. Aspirin alone is not enough to adequately reduce the risk of stroke. People need to follow the other proven methods: controlling blood pressure and diabetes, stopping smoking, eating correctly, and exercising.”

MORE THOUGHTS ON ASPIRIN RESISTANCE

Commenting on the research, Eric Topol, MD, Professor of Medicine and Chairman of the Department of Cardiovascular Medicine at the Cleveland Clinic, told Neurology Reviews that “the work that Dr. Alberts and his team reported in Vancouver is quite important—documenting the high frequency of patients who turn out to be nonresponders to aspirin. We have found a similar high rate of aspirin resistance in patients with coronary artery disease and have shown the considerable risk of not being responsive to aspirin during extended follow-up with respect to risk of death, heart attack, and stroke. Taking the work of Dr. Alberts coupled with ours at Cleveland Clinic, it appears it will be worthwhile to screen patients—at least the high-risk ones—at the time of initiating aspirin therapy. This will help in assessing the correct dose of aspirin and, if necessary, the need for using an alternative antiplatelet agent.”

NR

—Bruce Sylvester

Suggested Reading
Alberts MJ, Bergman DL, Molner E, et al. Antiplatelet effect of aspirin in patients with cerebrovascular disease. Stroke. 2004;35:175-178.

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