Aspirin Resistance Found in More Than One Quarter of Cardiac Patients on Aspirin Therapy

Martha Kerr

March 14, 2005

March 14, 2005 (Orlando) — Chinese investigators report finding a high prevalence of aspirin resistance in patients with cardiovascular disease on aspirin therapy. Aspirin resistance has been linked to an increased risk of adverse cardiac events.

Wai-Hong Chen, MD, from Queen Mary Hospital at The University of Hong Kong, and colleagues measured aspirin resistance in 468 patients with coronary artery disease using an investigational assay (Ultegra, Accumetrics, San Diego, CA). Overall, 27% had aspirin resistance, they found.

Those most likely to have resistance are those most at risk of mortality from their disease. Dr. Chen told attendees of the American College of Cardiology 2005 Annual Scientific Session that the elderly, women (46.1%), smokers (11.5%), diabetics (39.1%), those with hypertension (72.7%), hyperlipidemia (68.8%), renal insufficiency (18.8%), and low-dose aspirin (90.6%) had the highest incidence of resistance.

As noted, aspirin dose affected risk of resistance. The highest incidence of aspirin resistance occurred in those taking 100 mg daily or less, while no resistance was found in those taking more than 300 mg daily.

The Accumetrics assay measures aspirin-induced platelet dysfunction. Using the same test, a team at Baylor College of Medicine in Houston, Texas, led by Eli Lev, MD, showed that aspirin and clopidogrel resistance often occur together.

Of the 80 patients studied, 15% were found to be aspirin resistant, 24% were clopidogrel resistant, and 7.5% were found to be resistant to both.

Marc Sabatini, MD, instructor of medicine at Brigham and Women's Hospital and Harvard Medical School, noted in an interview with Medscape that "the field of aspirin and clopidogrel resistance is still developing.... We have to remember that not everyone will have the same degree of platelet aggregation to aspirin."

"Those with aspirin resistance are at increased risk of ischemic events," Dr. Sabatini continued. "We need to identify hyporesponders."

"The aspirin resistance test is not ready for prime time," Christopher Cannon, MD, associate professor of medicine of Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts, told Medscape. "It is still in the field of active research — but we are going in the right direction."

ACC 2005 Annual Scientific Sessions: Abstract 1043-126, presented March 6, 2005; abstract 868.7, presented March 9, 2005.

Reviewed by Gary D. Vogin, MD

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