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What Aspirin Dose Is Safest and Most Effective for Preventing Heart Disease?

Worst Pills, Best Pills Newsletter article May, 2009

Taking 75 to 81 milligrams of aspirin a day (one low-dose aspirin tablet) could be the safest, most effective way to prevent heart disease in patients who require aspirin therapy, according to a new study in the March 19, 2009, Annals of Internal Medicine.

The study also found that taking 100 milligrams or more of aspirin (EASPIRN, ECOTRIN, EMPIRIN, GENUINE BAYER ASPRIN) a day does not have any clear benefit for preventing heart disease — and it may actually be harmful to patients’ health.

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To determine the safest, most effective aspirin dose, researchers have just analyzed the data from CHARISMA, a major study from many medical centers completed several years ago that examined the effects of aspirin use with clopidogrel (PLAVIX). In the CHARISMA study, researchers sought to determine whether clopidogrel, when added to low-dose aspirin, improved the long-term outcome in patients with cardiovascular disease or multiple risk factors for cardiovascular events, compared to low-dose aspirin alone. The new Annals study re-examined those same data to figure out the safest, most effective aspirin dose.

Clopidogrel is a drug intended to reduce the risk of a new heart attack or stroke in patients with a history of a recent heart attack or stroke. The drug has also been approved by the Food and Drug Administration for a condition known as acute coronary syndrome in patients who may be treated medically, with a stent (a metal device placed in a coronary vessel to keep it open) or with bypass surgery to reduce the rate of heart attack, stroke and cardiovascular death.

The weight of the evidence indicates that there is a beneficial role for the short term use of clopidogrel and aspirin in acute situations, such as after the placement of a stent (a mesh tube to keep an artery open).

CHARISMA used the scientific "gold standard" methodology, which is a randomized controlled trial. In the trial, 15,603 patients were randomly assigned to receive either 75 milligrams of clopidogrel per day in combination with low-dose aspirin ranging from 75 milligrams to 162 milligrams, or a placebo plus low-dose aspirin. The patients were followed for a median of 28 months. The authors concluded that, "Overall, clopidogrel plus aspirin was not significantly more effective than aspirin alone in reducing the rate of myocardial infarction [heart attack], stroke or death from cardiovascular causes."

In this new study on aspirin dose, the authors concluded that the "most important safety concern about using doses of aspirin that are higher than necessary is aspirin’s dose dependent gastrointestinal toxicity."

Here, we are providing our readers with the Annals’ Summary for Patients on the follow-up study focusing on aspirin doses:

What is the problem and what is known about it so far?

Aspirin and clopidogrel are drugs that block the ability of platelets to stick together and form clots. Because the drugs prevent clotting, they may also cause bleeding. Doctors often prescribe daily aspirin to prevent future blood clots in people who have had or are at high risk for heart attacks and strokes. In these groups, the benefits of preventing clots outweigh the risk for bleeding.

However, different doses of aspirin may have different benefits and risks. For example, lower aspirin doses may cause less bleeding but may be less effective at preventing clots. Also, higher aspirin doses may be more effective at preventing clots but may cause more bleeding.

Why did the researchers do this particular study?

To see which dose of aspirin seems to be safest and most effective.

Who was studied?

Almost 15,600 people at risk for heart attack and stroke who were taking aspirin. All had been participants in a study of whether clopidogrel and aspirin prevented more heart attacks and strokes than aspirin alone.

How was the study done?

The researchers grouped together participants who were taking lower and higher aspirin doses. They then followed them over time and compared the number of people in each group who died or had heart attacks, strokes, or bleeding events.

What did the researchers find?

Outcomes did not obviously differ between people who took lower and higher aspirin doses. However, people who took higher aspirin doses together with clopidogrel may have been slightly more likely to die or have a heart attack, stroke, or bleeding event.

What were the limitations of the study?

The findings are not definitive because participants were not assigned at random to receive higher and lower aspirin doses.

What are the implications of the study?

Higher daily aspirin doses are not clearly better than lower doses. Higher doses may cause more harm, especially for people taking clopidogrel. Lower doses [75-81 milligrams a day] may be equally effective and safer.