Published Online
on December 11, 2003

A more recent version of this article appeared on January 1, 2004

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Submitted on August 28, 2003
Accepted on September 17, 2003

Antiplatelet Effect of Aspirin in Patients With Cerebrovascular Disease

Mark J. Alberts MD^*; Deborah L. Bergman RN, NP; Elise Molner RN; Borko D. Jovanovic PhD; Issei Ushiwata MD; and Jun Teruya MD

From the Department of Neurology, Northwestern University, Chicago, Ill.

^* To whom correspondence should be addressed. E-mail: m-alberts{at}northwestern.edu.

Background and Purpose--Aspirin is used commonly to prevent ischemic strokes and other vascular events. Although aspirin is considered safe and effective, it has limited efficacy with a relative risk reduction of 20% to 25% for ischemic stroke. We sought to determine if aspirin as currently used is having its desired antiplatelet effects.

Methods--We ascertained patients with cerebrovascular disease who were taking only aspirin as an antiplatelet agent. Platelet function was evaluated using a platelet function analyzer (PFA-100). PFA test results were correlated with aspirin dose, formulation, and basic demographic factors.

Results--We ascertained 129 patients, of whom 32% were taking an enteric-coated aspirin preparation and 32% were taking low-dose (162 mg/d) aspirin. For the entire cohort, 37% of patients had normal PFA-100 results, indicating normal platelet function. For the patients taking low-dose aspirin, 56% had normal PFAs compared with 28% of those taking 325 mg/d of aspirin, while 65% of patients taking enteric-coated aspirin had normal PFAs compared with 25% taking an uncoated preparation (P<0.01 for both comparisons). Similar results were obtained if PFA results were analyzed using mean closure times (low-dose aspirin, 183 sec; high-dose aspirin, 233 sec; enteric-coated, 173 sec; uncoated, 235 sec; P<0.01 for comparisons). Older patients and women were less likely to have a therapeutic response to aspirin, independent of aspirin dose or formulation.

Conclusions--A significant proportion of patients taking low-dose aspirin or enteric-coated aspirin have normal platelet function as measured by the PFA-100 test. If these results correlate with clinical events, they have broad implications in determining how aspirin is used and monitored.

Key words: antiplatelet therapy • aspirin • cerebrovascular disorders • stroke, ischemic

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