Everyone who has had a heart attack or stroke should take low-dose ASA for life because it can reduce the risk of deadly recurrence by up to 25 per cent.
But people who have no history of cardiovascular disease should not routinely take acetylsalicylic acid (brand name Aspirin and generics) as a preventive tool because there is no evidence the benefits of doing so outweigh the risks.
Also, people who do take ASA for their heart problems should be careful about using other painkillers such as ibuprofen, because they interfere with Aspirin's ability to prevent clotting.
Those are the three key messages that emerge from the first-ever guidelines on antiplatelet therapy, published on Monday by the Canadian Cardiovascular Society.
"The purpose of these guidelines is to ensure that antiplatelet therapy is used appropriately," Jean-François Tanguay, a cardiologist at the Montreal Heart Institute and co-chair of the expert committee that prepared the document, said in an interview.
He said that, generally speaking, too few patients who could benefit are taking ASA, and too many who have not had a heart attack or stroke are taking it inappropriately.
Antiplatelet therapy - drug treatment to prevent blood clots - is the cornerstone of treating patients who have survived a heart attack, stroke or who have peripheral artery disease. Yet, until now, there were no clear treatment guidelines.
Research has shown that 85 per cent of patients who have had serious cardiovascular problems such as a triple bypass are taking ASA, and in those with less serious problems, like heart attack or a blood clot, it's as little as 32 per cent.
"There is no reason it shouldn't be 100 per cent because the benefits are clear," Dr. Tanguay said.
At the same time, many physicians routinely tell their patients to start taking a baby Aspirin daily at age 50 to avoid heart problems. Antiplatelet therapy is also a common recommendation for post-menopausal women and diabetics. However, there is no good evidence that this is beneficial. And there is clear evidence that regular use of ASA (and other painkillers) can cause serious stomach problems.
"The guidelines don't say you should absolutely not take Aspirin, but this notion of giving it to everyone is not appropriate," Dr. Tanguay said. "It's also important that patients discuss the issue with their physician, because there are many subtleties."
"The CCS Guidelines for the Use of Antiplatelet Therapy in the Outpatient Setting are the first and only of their kind in the world," said Alan Bell, a Toronto family doctor and co-chair of the committee. "Unlike other disease-based documents, this paper is treatment-based."
He said the document is aimed at specialists and general practitioners alike, to ensure that everyone has the most up-to-date information on this important issue.
In addition to the broader issues of interest to the public, the guidelines touch on specific conditions that make antiplatelet therapy challenging, such as how to treat women who are pregnant and those with various chronic health conditions. One of the biggest challenges when prescribing ASA or other anti-clotting drugs is drug interactions.
For example, many people with osteoarthritis take painkillers that can block the beneficial effects of ASA in cardiovascular patients. The guidelines note, for example that ASA should not be taken at the same time as ibuprofen or Celebrex.
The cardiovascular society has also developed a number of tools to make the guidelines easier to use in clinical practice, including a smartphone app, educational podcasts and a pocket reference card for physicians.
About 1.3 million Canadians have heart disease, and another 317,500 are living with the effects of a stroke. In 2007, the most recent year for which there are detailed data, 69,503 people died from heart disease and strokes, according to Statistics Canada.