Researchers: Aspirin Resistance Real

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Patients who exhibit this trait are at higher risk of stroke, MI, graft failure, meta-analysis reveals.

SAN FRANCISCO—Aspirin resistance is real and it is associated with higher risk of cardiovascular- and cerebrovascular events.

"We call it aspirin non-responsive," said lead investigator George Krasopoulos, MD, PhD, senior registrar at Royal Brompton Hospital in London, UK. "If you have this, then you are six times at greater risk of dying and four times at greater risk of developing any cardiovascular clinical event. You also have four times the risk of developing acute coronary syndrome. If you are female or you have renal failure, you have a higher chance of being aspirin resistant."

He and his colleagues performed a meta-analysis of data from 19 clinical trials that included 2,696 patients who received aspirin to manage cardiovascular or cerebrovascular disease. Of the 19 studies with aspirin regimes ranging from 75 mg a day to 500 mg three times a day, three studies included adjunct antiplatelet therapy.

The investigators defined aspirin resistance as a demonstrative platelet response to specific stimuli despite aspirin therapy and defined "aspirin sensitive" as the expected inhibitory platelet response to specific stimuli with aspirin therapy. Dr. Krasopoulos, who reported the findings here at the American Stroke Association's International Stroke Conference, said most of the studies used platelet aggregometry or the PFA-100 or PFA-100-like assays to detect aspirin resistance.

The investigators identified 758 patients (26%) who were aspirin resistant. The meta-analysis revealed that 41% of these patients suffered either a stroke, MI, acute coronary syndrome, or a graft failure compared with 17% of the 1,938 aspirin-sensitive patients.

"Nephrologists need to be aware of this because a significant number of patients with renal impairment may have aspirin resistance," Dr. Krasopoulos said.

"They may have to prescribe a second antiplatelet or may need to prescribe a combination of antiplatelet medications to protect these patients from adverse clinical outcomes. I think physicians should screen for aspirin resistance."

Stephanie Brister, MD, associate professor at the University of Toronto, said the concept of aspirin resistance is highly controversial. "We think there is evidence that aspirin resistance is real."

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