The conclusion about coated aspirin was only one finding in the study, whose main goal was to test the hotly disputed idea that aspirin does not help prevent heart attacks or stroke in some people.
For more than a decade, cardiologists and drug researchers have posited that anywhere from 5 to 40 percent of the population is “aspirin resistant,” as the debated condition is known. But some prominent doctors say that the prevalence of the condition has been exaggerated by companies and drug makers with a commercial interest in proving that aspirin — a relatively inexpensive, over-the-counter drug whose heart benefits have been known since the 1950s — does not always work.
The authors of the new study, from the University of Pennsylvania, claim that they did not find a single case of true aspirin resistance in any of the 400 healthy people who were examined. Instead, they claim, the coating on aspirin interfered with the way that the drug entered the body, making it appear in tests that the drug was not working.
The study was partly financed by Bayer, the world’s largest manufacturer of brand-name aspirin, much of which is coated.
Aside from whether coating aspirin conceals its effects in some people, there is little evidence that it protects the stomach better than uncoated aspirin, said Dr. Garret FitzGerald, chairman of pharmacology at the University of Pennsylvania and one of the study’s authors.
“These studies question the value of coated, low-dose aspirin,” he said in a statement accompanying the article. “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.”
In a statement, Bayer took issue with some of the study’s conclusions and methods and said previous studies of coated aspirin, also called enteric-coated aspirin, have been shown to stop blood platelets from sticking together — which can help prevent heart attacks and stroke — at levels comparable to uncoated aspirin. Bayer also noted that the price difference between its coated and uncoated aspirin was negligible, although Dr. FitzGerald argued there was no reason patients should use anything other than uncoated generic aspirin, which is cheaper.
“When used as directed,” the company said, “both enteric and nonenteric coated aspirin provides meaningful benefits, is safe and effective and is infrequently associated with clinically significant side effects.”
Although researchers had long observed that, as is true with most drugs, aspirin’s effects varied among patients, the existence of “aspirin resistance” gained currency in the 1990s and early 2000s. One often-cited study, published in 2003, found that about 5 percent of cardiovascular patients were aspirin-resistant and that that group was more than three times as likely as those not aspirin-resistant to suffer a major event like a heart attack.
But some said the popularity of aspirin resistance got a boost in part because of the development of urine and blood tests to measure it and the arrival on the market of drugs like Plavix, a more expensive prescription drug sold by Bristol-Myers Squibb that also thins the blood.
In the most recent study, the patients who initially tested positive for aspirin resistance later tested negative for it and by the end of the study, Dr. FitzGerald said, none of the patients showed true resistance. “Nobody had a stable pattern of resistance that was specific to coated aspirin,” he said. If resistance to aspirin exists, he said, “I think that the incidence is vanishingly small.”
Dr. Eric Topol, one of the authors of the 2003 study, said he strongly disagreed with Dr. FitzGerald’s conclusions, noting that it looked only at healthy volunteers, “which is very different than studying people who actually have heart disease or other chronic illnesses who are taking various medications.” Those conditions or medications could affect the way aspirin works in the body, he said.
But Dr. Topol and Dr. FitzGerald did agree that there was little value in testing for whether someone was aspirin-resistant, in part because there was little evidence that knowing someone is resistant to aspirin will prevent a heart attack or stroke.
Representatives for Accumetrics, which sells a blood test, and Corgenix, which sells a urine test, maintained that there was value in determining how well aspirin worked in individual patients, and said more recent research on the issue has moved away from a stark determination of whether someone is resistant to aspirin. “This whole concept of drug resistance has moved past that term and moved into the level of response that someone has,” said Brian Bartolomeo, market development manager at Accumetrics.
