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Aspirin resistance may be misdiagnosed in some patients
Several factors can contribute to an incorrect classification of aspirin resistance.
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A single measurement of platelet aggregation may not be enough to determine if a patient is classified as aspirin resistant, according to data reported at the 23rd American Society of Hypertension Annual Scientific Meeting in New Orleans.
Carlo Patrono, MD, professor of pharmacology at the Catholic University of Rome in Italy, cited findings from several studies that suggested that measurement of only one level of platelet aggregation may lead physicians to misdiagnose certain patients as aspirin resistant.
“Aspirin resistance, as defined by platelet aggregation measurement, is not a clinical diagnosis, and a number of current guidelines issued by the American College of Chest Physicians, the European Society of Cardiology, and the International Society for Thrombosis and Hemostasis recommend against testing for or changing therapy in light of this ill-defined phenomenon,” Patrono said.
Multiple measurements
Patrono cited data from one study of 48 healthy people who received 100 mg doses of aspirin for a duration of eight weeks. The participants were divided into multiple groups, and each group was evaluated for different measurements of platelet aggregation response. Measurements were categorized by the researchers as aspirin sensitive or aspirin resistant.
“We categorized more than 200 measurements as being aspirin sensitive or aspirin resistant based on rate thresholds that have been defined in the literature for aspirin resistance,” Patrono said. “Our numbers indicated that anywhere between 2% and 35% of these 200 measurements were classified based on the dichotomous definition of being ‘aspirin resistant,’ and depending on which assay you are using, you will get a different number.” Moreover, he noted that “aspirin resistance is not a stable phenotype, as indicated by repeated measurements of platelet function in the same subjects.”
Patrono also suggested that physicians be aware of the effects of certain drug interactions that may inhibit the effects of aspirin. He specifically noted that ibuprofen and naproxen can inhibit the antiplatelet effects of aspirin when taken in combination with aspirin.
Patrono also suggested that interpreting treatment failure as an indicator of aspirin resistance and as a catalyst for the changing of therapeutic regimens was not justified, given the multifactorial nature of atherothrombosis.
“There is no scientific basis for changing antiplatelet therapy in the face of a treatment failure because we cannot be sure whether a second vascular event will share the same components of the causal mechanism that led to the first event,” Patrono said. “We have no convincing evidence that changing therapy is a more effective strategy than maintaining an evidence-based antiplatelet regimen.” – by Eric Raible
For more information:
- Patrono C. Aspirin resistance in stroke and CVD: Fact or fiction? Presented at the 23rd American Society of Hypertension Annual Scientific Meeting; May 14-17; New Orleans.