Millions of Americans take low-dose aspirin every day to prevent heart attacks and strokes. But a study published last week challenges some cherished beliefs about the familiar remedy, leaving some consumers to wonder if they should throw out their coated pills and others concerned that they unnecessarily may be taking expensive substitutes.
The study, published in the journal Circulation, by researchers at the University of Pennsylvania, tested 400 healthy people for evidence that aspirin did not work in them, a phenomenon called “aspirin resistance.” Aspirin prevents blood platelets from sticking together, which can lead to heart attacks and strokes. Previous studies have estimated that anywhere from 5 to 40 percent of the population is resistant to aspirin’s effects.
But the study essentially found that the condition doesn’t exist: they could not document a single case of true aspirin resistance in their sample. What had appeared to be aspirin resistance, they said, actually was caused by the coating commonly used on aspirin pills intended to protect the stomach. The coating slowed the drug’s absorption into the body.
The study didn’t evaluate whether coated aspirin was less likely to prevent heart attacks or strokes, said Dr. Garret FitzGerald, one of the authors. And people who took the coated aspirin in his study eventually showed a response to it.
But people who seek out coated aspirin may be doing so unnecessarily, he said, especially since previous studies have not consistently shown that the coating even prevents gastric problems.
“There’s no rationale for you to be on coated aspirin,” said Dr. FitzGerald, who is a cardiologist and chairman of pharmacology at the University of Pennsylvania.
Some cardiologists have begun advising patients to seek out uncoated aspirin because other studies have suggested that the uncoated type may be more effective. But finding it isn’t so easy. Even cheaper store brands, like those sold by CVS and Wal-Mart, come with a so-called enteric coating. One of the few uncoated aspirins on the market is St. Joseph’s chewable variety — the old orange-flavored baby aspirin.
But other experts, like Dr. Steven E. Nissen, a cardiologist at the Cleveland Clinic, see no real harm in taking coated aspirin, which is cheap and readily available. Many major studies of aspirin have been conducted using the coated variety.
The new study also calls into question the very idea of aspirin resistance. Testing for the condition became more widespread in the early 2000s, as expensive prescription alternatives like the blood thinner Plavix (also called clopidogrel) gained popularity. Many cardiologists suspected that the timing was not a coincidence.
“Before clopidogrel, we had never heard of aspirin resistance,” said Dr. Sanjay Kaul, a cardiologist at Cedars-Sinai Medical Center in Los Angeles. “It seemed to be that this was driven mostly by marketing considerations.” The new study raises the possibility that many patients may have been falsely told that aspirin doesn’t work on them, Dr. Kaul and other experts said.
The University of Pennsylvania study was partially financed by Bayer, the world’s largest manufacturer of branded aspirin, much of which is coated. In a statement, Bayer challenged some of the study’s conclusions and methods, and also said there was evidence that the enteric coating can reduce gastric side effects.
Critics of Dr. FitzGerald’s study also argue that he should have studied aspirin resistance in patients with conditions like heart disease, rather than in healthy people.
But even these critics acknowledge that testing for resistance is probably not worthwhile. Dr. Nissen, who is critical of Dr. FitzGerald’s study, doesn’t test his patients for aspirin resistance. But he said he would be reluctant to switch a patient from another drug back to aspirin now if a test had previously shown they were aspirin-resistant. Changing treatments is always risky, he said.
“If the patient is not bleeding, is not having a complication, am I going to take it away?” Dr. Nissen wondered. “That’s the dilemma we face.”
News Analysis: A Debate on Coated Aspirins and Aspirin Resistance
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News Analysis: A Debate on Coated Aspirins and Aspirin Resistance
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News Analysis: A Debate on Coated Aspirins and Aspirin Resistance
