Published: Jan. 9, 2008
Updated: Jan. 10, 2008
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By Duke Medicine News and Communications
DURHAM, NC – When it comes to aspirin, less is more in the early treatment of a heart attack, say researchers at Duke University Medical Center. But many physicians may not be getting the message.
In a study appearing in the January 15 issue of the journal Circulation, researchers show that a low dose of aspirin appears to be just as effective as a higher dose of the drug in the initial treatment of ST-elevation myocardial infarction (STEMI), one of the most common types of heart attack. They also say a lower dose is safer, because it is associated with less bleeding.
"We have known for almost 20 years that a low-dose of aspirin (162 milligrams) given in the early stages of a heart attack can save lives," says Jeffrey Berger, MD, a cardiologist at Duke and lead author of the study. "Yet the majority of the doctors in this country are still prescribing 325 milligrams despite the lack of evidence showing that more is better."
Aspirin is one of the most widely prescribed drugs in the world, and Berger says people -- physicians included -- may underestimate its power. "We know that a single dose of just 100 milligrams of aspirin can completely block within minutes the formation of blood clots," he says. That's critical in treating a heart attack because clots can clog arteries and block blood from reaching the heart.
But taking aspirin comes at a cost. The very same mechanism that can break up life-threatening clots can increase the chance of serious bleeding, which could lead to the need for a transfusion, a stroke or even death. "So we need to be very careful in how much aspirin we prescribe," says Berger.
Berger led a team of researchers in reviewing the effects of a low versus a high dose of aspirin in nearly 50,000 patients suffering from STEMI in two international trials. Three-quarters of the patients got a low dose of aspirin (162 mg or less) and the rest got a higher dose. Investigators tracked death rates and episodes of serious bleeding in both groups for up to 30 days following therapy.
They found no difference between the two groups in terms of short-term outcomes, except for a difference in bleeding: Those patients who took the higher dose of aspirin had significantly more bleeding than those who took the lower dose.
The study does not provide the definitive answer regarding dosing because it was observational in nature, and the participants in the trials were not randomized to preset dosing levels or compared with controls. Still, Berger feels it offers enough evidence to suggest that clinicians take another look at their practice.
"If a lower dose of aspirin is just as good -- and more may be harmful -- why risk it?"
Doctors may be over prescribing aspirin simply because of the say it is manufactured and sold, says Berger. The most common and easily used form of aspirin on the market is either an 81 or a 325 milligram tablet - no single, 162 milligram product is readily available. In addition, Berger says physicians who already realize that 162 milligrams is effective, might simply assume that twice as much is better, despite evidence to the contrary.
Co-authors of the study include Christopher Granger, Eric Ohman, Robert Harrington, Robert Califf, Amanda Stebbins and senior author, Eric Peterson, all from Duke Clinical Research Institute; Paul Armstrong, from the University of Alberta; Frans Van der Werf, of Gasthuisberg University Hospital, Belgium; Harvey White, from Auckland City Hospital, New Zealand; and R. John Simes, from the University of Sydney.