WESTPORT, CT (Reuters Health) Oct 02 - Daily low-dose aspirin offers far less
protection against ischemic stroke in post-MI patients than intermediate-dose
aspirin, research results suggest.
"It looks like from this analysis that the smallest amount of aspirin
that [post-MI] patients should take is 160 mg," Dr. Christopher M. O'Connor
of Duke University Medical Center, Durham, North Carolina, said in a telephone
interview with Reuters Health.
The importance of aspirin dose in post-MI patients emerged in a secondary
analysis of the Warfarin Aspirin Reinfarction Study. In the initial study
of 8803 post-MI patients, aspirin 160 mg monotherapy was superior to the combination
of warfarin (1 or 3 mg) plus 80 mg aspirin for reducing cardiovascular morbidity
and mortality.
In the secondary analysis, the team determined the effect of aspirin dose
on ischemic stroke in patients randomized to warfarin 1 mg plus aspirin 80
mg versus those randomized to aspirin 160 mg.
"We have never really fully understood whether there was a dose-response
relationship between aspirin dose and clinical outcome," Dr. O'Connor
told Reuters Health. "This is one of the first studies to suggest that
there is a difference between different aspirin doses and that difference
can affect stroke rates."
In the September 1st issue of the American Journal of Cardiology, he
and his colleagues report a two-fold increase in the risk of ischemic stroke
in the aspirin 80 mg plus warfarin arm of the trial compared with the aspirin
160 mg arm. The rate of stroke at 1 year was 1.1% in the aspirin 80 mg plus
warfarin arm compared with 0.6% in the aspirin 160 mg arm (p = 0.0534).
Aspirin dose was an independent predictor of ischemic stroke, the researchers
determined. They note that, in particular, the highest-risk patients--male
patients and those with Q-wave MI--appeared to derive greater benefit from
aspirin 160 mg than from the combination of aspirin 80 mg and warfarin 1 mg.
They believe that as many as 30% of patients receive inadequate doses of aspirin
after MI, largely because of "unproven concerns about excess risk."
In this study, the rate of hemorrhage was "quite small" and was
similar for the 80-mg and 160-mg aspirin doses.
Am J Cardiol 2001;88:541-546.
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