Study Questions Aspirin Resistance And Benefits Of Coating Tablets

Connie K. Ho for — Your Universe Online

One out of 5 U.S. adults take aspirin on a daily basis. With this in mind, scientists from the Perelman School of Medicine at the University of Pennsylvania (UPenn) set out to study “aspirin resistance” and discovered that resistance to low-dose aspirin therapy is not all that common. Experts say this calls into question the common practice of using blood and urine screens to test for aspirin resistance.

According to The New York Times, the study was partially funded by aspirin manufacturer Bayer and the results of the study were recently published in the journal Circulation. Aspirin has been used for years for its benefits in the prevention of heart disease. For people who have suffered a heart attack, taking low-dose aspirin can help reduce the possibly of a second heart attack by approximately one fifth.

Previous prevention studies have found that, for patients who have never had a heart attack, taking low-dose aspirin can reduce the risk of having a heart attack about the same amount as the risk of causing the person´s stomach to bleed.

“The incidence of true aspirin resistance is vanishingly small, and the idea of testing for it is seriously undermined by this study,” commented Dr. Garret FitzGerald, director of the Institute for Translational Medicine and Therapeutics at UPenn, in an article on

In the study, the researchers looked for patients who had a genetic resistance to aspirin. They examined 400 healthy volunteers who considered themselves to be truly resistant to the advantages of using aspirin due to their consistently weak anti-clotting ability. They also looked at two tests that were thought to diagnose a patient´s aspirin resistance. One screening technique was a blood test and another was an FDA-approved urine test that looks for an indirect marker of platelet stickiness.

The scientists did not find “aspirin resistance,” but they did discover people who had “pseudoresistance” based on aspirin´s ability to possibly protect the stomach. As such, neither screening test was supported in the study.

“When we looked for aspirin resistance using the platelet test, it detected it in about one-third of our volunteers,” explained Dr. Tilo Grosser, a research assistant professor of Pharmacology at UPenn, in a prepared statement. “But, when we looked a second time at the incidence of aspirin resistance in the volunteers, the one-third that we measured who was now resistant was mostly different people. Nobody had a stable pattern of resistance that was specific to coated aspirin.”

The team of investigators also decided to compare the result of coated aspirin along with regular uncoated aspirin in a volunteer subgroup. They found that the coating slowed down the absorption compared to the uncoated aspirin, which caused a false view of aspirin resistance for people who were taking the coated aspirin. Coated aspirin is more expensive than the cheap, generic version of uncoated aspirin, but the coated aspirin did not prove to decrease the possibly of serious stomach bleeds as compared to uncoated aspirin.

“These studies question the value of coated, low-dose aspirin,” remarked FitzGerald, an expert on blood clotting, in the statement. “This product adds cost to treatment, without any clear benefit. Indeed, it may lead to the false diagnosis of aspirin resistance and the failure to provide patients with an effective therapy. Our results also call into question the value of using office tests to look for such resistance.”

Others have contested the results of the study.

“Obviously, this study was in healthy volunteers, so it’s a bit difficult to make a direct translation to patients with a stroke or cardiac event,” said Brian Bartolomeo, market development manager for Accumetrics, the company that makes the blood tests.

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