American College of Physicians: Internal Medicine — Doctors for Adults ®


Do your patients need aspirin therapy? Ask them

From the March ACP-ASIM Observer, copyright 2002 by the American College of Physicians-American Society of Internal Medicine.

By Deborah Gesensway

The pros and cons of aspirin
Risk calculators on the Web

When the U.S. Preventive Services Task Force unveiled a new guideline earlier this year urging adults at risk of having a first heart attack in the next five years to take a daily dose of aspirin, the advice seemed to make perfect sense.

A daily dose of aspirin, after all, has long been viewed as a safe and effective way to reduce secondary heart attack risk, and the guideline cited data from recent studies that expanded the notion to primary prevention of heart attacks. If 1,000 people with a 3% chance of suffering a non-fatal heart attack in the next five years took an aspirin a day, those studies estimated, between four and 12 of them would probably avoid a serious cardiovascular event. (The guideline is online at

Aspirin prophylaxis, however, has a downside. Between two and four of those same 1,000 individuals, for example, are likely to wind up in the hospital with major gastrointestinal bleeding, while another one will probably have a life-threatening hemorrhagic stroke.

As a result, physicians trying to decide which patients to put on aspirin face a more difficult task than they might think. While the vast majority of patients who take a prophylactic dose of aspirin will be neither harmed nor helped, it is also impossible to predict exactly who will gain or lose from aspirin therapy.

So how do you put the guideline into practice? Experts say that because the evidence about using aspirin for primary prevention is not overwhelming, you need to work with your patients to balance the risks and benefits. Fortunately, easy-to-use tools are readily available to help you.

Patients as decision-makers

The task force guideline, which appeared in the Jan. 15, 2002, Annals of Internal Medicine (, suggested a fairly simple strategy: Give your patients the data and decide together. Show patients that they have a 2% risk of having a heart attack, for instance, instead of telling them that their heart attack risk is "moderate" or "high."

Alfred O. Berg, MD, a family physician at the University of Washington in Seattle and chair of the task force, said that aspirin's potential to cause harm, no matter how small, means that physicians should respect patients' wishes about its use. "Aspirin is not for everybody," he explained. "We may have better information now, but there still isn't enough information to make a categorical judgment like, 'This person ought to be on aspirin.'"

That's why the task force recommended that physicians ask patients "to think about whether they fear heart attacks more than they fear developing GI bleeds and bleeding strokes," Dr. Berg said. "We can give people the numbers, but the individual patient has to put values on them and make the final decision."

Cynthia D. Mulrow, FACP, a member of the task force and a co-author of a background paper analyzing the evidence on aspirin's effectiveness in the Jan. 15 Annals, said that the task force guideline includes a chart that quantifies the risks and benefits of aspirin therapy. "We want people to think more about quantifying their risk," said Dr. Mulrow, who is also a Deputy Editor for Annals and clinical professor of medicine at the University of Texas Health Science Center at San Antonio.

To bring patients into the decision-making process, Dr. Mulrow said, use the chart shown on this page, "The pros and cons of aspirin." You'll also need to find a Web-based cardiac risk calculator to determine patients' heart attack risk. (See "Risk calculators on the Web," below.)

To use the risk calculator, simply fill in information about the patient's age, blood pressure and cholesterol level, and check boxes for the patient's sex and history of smoking and diabetes. The whole process takes about 30 seconds. Patients can complete the form themselves or a nurse can fill it in while taking vital signs.

The risk calculator instantly analyzes the data and shows patients their chance of having a heart attack in the next five years. If their risk is 5%, for example, you can then use the guideline chart to show patients the risks and benefits of aspirin therapy.

This process allows patients to think through their concerns and make a choice: Do they want to take a chance that they'll be one of the six to 20 people out of 1,000 who will avoid a heart attack by taking an aspirin a day? Or are they more worried that they will be one of the two to four people hospitalized with a GI bleed, or one of the two people who is likely to bleed into the brain?

Risk calculators can also show patients the benefits of other cardiovascular risk reduction therapies. Michael P. Pignone, ACP-ASIM Member, assistant professor of medicine at the University of North Carolina, Chapel Hill, and a co-author of the clinical guideline's background paper, said that some risk calculators (like the one he has created at give patients a detailed look at how they can lower their cardiac risk by making lifestyle changes like stopping smoking.

"If a patient's five-year risk is 10%, you could show that taking aspirin daily would reduce that risk by about 28%, bringing it down to 7%," he explained. "You could then show him that if he took a lipid-lowering drug, he could reduce his risk another 30%, to about 4.5%," he said. "The same is true if he stopped smoking."

Flawed data?

While the evidence for primary prevention is not as overwhelming as data supporting secondary prevention, advocates of aspirin prophylaxis say it is strong enough to show that a daily, low dose of aspirin is the right therapy for many patients at risk of suffering a heart attack in the next five years. Some physicians, however, read the data differently. They contend that the evidence of aspirin's efficacy for primary prevention is overstated and that its risks are underestimated.

One vocal critic, John G. F. Cleland, MD, said that his interpretation of the data shows that the therapy reduces only the number of diagnosed heart attacks, not attacks overall. In an editorial in the Jan. 12, 2002, British Medical Journal (BMJ), he explained that aspirin merely masks heart attacks, producing a "cosmetic" blip in epidemiological statistics.

How could aspirin hide a heart attack? Dr. Cleland, professor of cardiology at the University of Hull in Kingston-upon-Hull in Great Britain, said that 25% of people who have what later turns out to be a heart attack don't recognize the signs anyway. Because aspirin can be an analgesic, it may further mask those symptoms. In addition, he said, some of the symptoms patients think are dyspepsia caused by aspirin may actually be due to a heart attack.

Dr. Cleland added that aspirin's ability to cover up early, nonfatal heart attacks could have dangerous consequences. These patients may not get the secondary prevention therapies proven to prevent some of the second—and fatal-heart attacks that many of them will experience.

In addition, he said, none of the large aspirin studies have shown any effect on mortality, a point also made in the new U.S. Preventive Services Task Force guideline. If aspirin was truly preventing heart attacks, Dr. Cleland said, and not just changing how they present, "you would expect a reduction in mortality." Supporters of the aspirin guideline counter that it's difficult to show an effect on mortality in generally healthy people in only five years.

While Dr. Cleland argues that aspirin may be useless or dangerous in the long run, he also has more immediate concerns about the safety of taking aspirin daily. The clinical trials used to create the guideline, he said, excluded patients with histories of peptic ulcer disease. As a result, researchers understated the risk of GI bleeds, particularly in older patients. He pointed out that studies have also demonstrated an increase in chronic renal failure among cardiovascular prophylactic aspirin users.

Safety issues

Dr. Cleland's views on aspirin therapy may run counter to mainstream thinking. (A series of letters published on the BMJ's Web site in response to his editorial attacked his hypothesis, saying it was based on flawed data.) Nonetheless, he points out certain safety issues that cannot be ignored. While some obvious groups of patients should avoid aspirin—such as people already taking blood thinners like warfarin—the evidence is less clear for others. Experts suggested paying particular attention to the following factors:

  • Age. If the patient is older than 70, Dr. Pignone said, the risks of aspirin's dangerous side effects increase, possibly doubling or tripling. The problem is that as those risks increase, so do the benefits, largely because age is a risk factor for heart attack. No good evidence exists to guide decision-making with older patients because the trials analyzed for the new guideline did not study this group. Complicating matters, risk calculators are not accurate for patients over 75.

  • High blood pressure. Before you start a patient on aspirin therapy, remember that hemorrhagic strokes are more likely to occur in patients with uncontrolled high blood pressure. "Most people with a blood pressure problem would benefit from aspirin, but we recommend that you try to control blood pressure before starting aspirin," Dr. Mulrow said. Blood pressure greater than 160 over 90 seems to be the threshold where problems begin, Dr. Pignone added.

  • NSAIDs. If patients are taking non-steroidal anti-inflammatory drugs (NSAIDs), bleeding risks increase. Dr. Mulrow said she always makes sure that patients who take Motrin or another NSAID understand that the drugs are not interchangeable with aspirin. (Many patients, she has found, do not know that NSAIDs are not likely to prevent heart attacks.) Be sure to recommend that patients who can clearly benefit from aspirin switch to acetaminophen for pain relief.

    Researchers have also questioned whether one NSAI—ibuprofen—interferes with aspirin's ability to thin blood. A study in the Dec. 20, 2001, issue of The New England Journal of Medicine found that when aspirin and ibuprofen were taken together, aspirin lost its effectiveness. Researchers also noted, however, that when aspirin was given two hours before ibuprofen, aspirin retained its blood-thinning properties. Dr. Pignone called the finding "preliminary, but worth further study."

  • ACE inhibitors. Evidence does not seem to show any interaction between aspirin and blood pressure-lowering or cholesterol-lowering drugs. But Dr. Pignone said there has been concern that aspirin may "blunt" the effect of ACE inhibitors in congestive heart failure patients who take both drugs. "This concern is more theoretical than proven," he added, "It's the kind of question that needs to be answered."

Nuts-and-bolts considerations

Finally, in terms of dosages, the task force did not find any benefit to higher doses of aspirin for primary prevention. Researchers found that the 81-mg version sold as "adult low-strength aspirin" works as well as higher doses. There is no benefit to buying the more expensive "buffered" or enteric-coated aspirin, Dr. Mulrow said, because side effects are not reduced.

No initial loading dose is required. If therapy needs to be stopped—either because of side effects or impending surgery—physicians should remember that because aspirin works by permanently altering platelets, it will take about 14 days for patients' platelets to work as they would without aspirin.

The bottom line, Dr. Berg said, is that aspirin is a powerful drug and physicians need to monitor its effects in patients. Physicians should also revisit the risk assessment calculator and rethink their decisions with patients every five years, or more frequently if health conditions change.

"Many patients don't consider aspirin a drug," he said, "so you have to ask about it specifically every so often to make sure that you and the patient agree it should be taken." Given the amount of evidence we now have about its serious side effects, he added, physicians should try to ascertain how many of their patients self-medicate with aspirin.

"Aspirin is not a magic pill, but it's remarkably effective," Dr. Pignone said. "It's a powerful medicine, and we need to think about it that way. It would never be over-the-counter if it came on the market today."

Deborah Gesensway is a freelance writer in Glenside, Pa.

The information included herein should never be used as a substitute for clinical judgment and does not represent an official position of ACP-ASIM.


The pros and cons of aspirin

The following estimates come from studies where aspirin was given for five years to 1,000 people with various levels of baseline risk for coronary heart disease. These data assume a relative risk reduction of 28% in patients taking aspirin, and they assume that risk reduction does not vary significantly by age.

Outcomes     Coronary heart disease risk over five years
  1% 3% 5%
Total mortality No effect No effect No effect
CHD events1 1-4 avoided 4-12 avoided 6-20 avoided
Hemorrhagic strokes2 0-2 caused 0-2 caused 0-2 caused
Major GI bleeding3 2-4 caused 2-4 caused 2-4 caused


1 Includes nonfatal myocardial infarction and fatal coronary heart disease. Five-year risks of 1%, 3% and 5% equal 10-year risks of 2%, 6% and 10%, respectively.
2 Increases in hemorrhagic strokes may be offset by reduction in other types of stroke in patients at very high risk for cardiovascular disease.
3 Rates may be two to three times higher in patients 70 and older.

Source: U.S. Preventive Services Task Force/Agency for Healthcare Quality Research.


Risk calculators on the Web

The following Web sites offer risk calculators to show patients their risk of experiencing a heart attack:

The following sites offer versions that you can load onto a handheld computer:


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