Tuesday November 3 2009
Experts have warned that “healthy people should not take aspirin to prevent a heart attack because routinely taking the drug does them more harm than good,” according to The Daily Telegraph.
Several newspapers covered this publication, which is not new research but a review of the existing evidence and expert opinion. It concluded that, for healthy people, the potential harms of aspirin may outweigh its potential benefits.
The question of whether healthy people should take aspirin as a preventative measure is a difficult one due to the fine balance between benefits and risks. At present, doctors decide whether patients should routinely use aspirin on a case-by-case basis.
Future updates of treatment guidelines, such as those produced by NICE (National Institute for Health and Clinical Excellence), will take into account emerging evidence such as the studies highlighted in this review.
Where did the story come from?
The review article was published in the Drug and Therapeutics Bulletin (DTB), a journal produced by the BMJ Group. This journal publishes evaluations of treatments and practical advice for healthcare professionals. The DTB is independent from the government and regulatory authorities, the pharmaceutical industry and commercial sponsorship.
The articles in the journal are not attributed to individual authors but are produced by a group of experts, commentators and editors. Articles are commissioned from expert authors, edited and then made available for critical review by selected commentators. These include the advisory council and editorial board of the DTB, experts in the field, GPs, pharmacists, nurses, pharmaceutical company representatives (if the company’s drug is discussed), national healthcare bodies (the MHRA and BNF), relevant consumer and patient groups, and a lawyer. Relevant comments are then integrated into the article.
The news reports that covered this article are generally accurate and balanced.
What kind of research was this?
This narrative review examined whether people who have not had a cardiovascular event (such as a heart attack) should use low-dose aspirin to prevent one from occurring. This is known as primary prevention.
The review takes into account current research evidence and opinion from various commentators. The review is not a systematic review, which means that it may have missed some relevant evidence.
What did the research involve?
The DTB reviews mainly include fully published research, with the most weight given to double-blind randomised controlled trials, systematic reviews or meta-analyses published in peer-reviewed journals. These study designs generally produce the most robust evidence for the effects of treatments, so relying on these types of study is appropriate. The conclusions of the article are based on a weighted assessment of the evidence identified and the opinions gathered.
Although literature searches may be carried out as part of the drafting of DTB articles, and commentators can identify any missing evidence, these articles are not systematic reviews and may miss some relevant research.
What were the basic results?
The review notes that aspirin is not specifically licensed for use as primary prevention in the UK. However, various guidelines from bodies including NICE and its Scottish equivalent (SIGN) recommend low-dose aspirin for primary prevention in certain groups of people. In general, aspirin is recommended for people at higher risk of cardiovascular events due to risk factors such as type 2 diabetes and high blood pressure.
The article discusses evidence that was published before these guidelines as well as more recent evidence.
Evidence published before the guidelines included the following:
- One meta-analysis of 195 studies compared aspirin or other antiplatelet treatment with control in 135,640 people at high risk of cardiovascular events. The majority of people in this analysis had already had a cardiovascular event. The study found that, compared to control, antiplatelet treatment reduced the risk of serious vascular events (from 13.2% to 10.7%) but increased the risk of major bleeding (not in the brain) (from 0.71% to 1.13%). The researchers recommended that taking 75–150mg of aspirin daily (or some other effective antiplatelet treatment) should be considered routinely for all patients with a high or intermediate risk of cardiovascular events, including those who had not yet had an event.
- Four meta-analyses looked specifically at aspirin for primary prevention. These reached various conclusions, but in general suggested that the potential benefits of aspirin in reducing cardiovascular events should be weighed up against the potential increase in risk of bleeding. Some concluded that aspirin might be beneficial for people whose risk of cardiovascular events was judged to be above a certain threshold level.
- One systematic review concluded that aspirin did not reduce the likelihood of stroke or cardiovascular events as a whole in patients with elevated blood pressure but no previous cardiovascular disease. It recommended that aspirin should not be used as primary prevention in this group.
- One randomised controlled trial (RCT) found that aspirin did not reduce the risk of death, heart attack or stroke in people with diabetes. Some of these people already had cardiovascular disease.
More recent evidence included the following:
- One meta-analysis pooled six RCTs which assessed aspirin for primary prevention in 95,000 people. The analysis used data from individual patients within each trial, which has advantages over using pooled results from each trial. It found that aspirin reduced the risk of serious vascular events from 0.57% a year to 0.51% a year, mainly due to a reduction in non-fatal heart attacks. This reduction did not vary significantly between people who had different ages, gender, blood pressure, history of diabetes or predicted risk of coronary heart disease. However, aspirin also increased the chance of having a major gastrointestinal or other bleed (not in the brain) from 0.07% a year to 0.10% a year. These figures mean that for every 3,300 people taking aspirin as primary prevention, one extra case of these serious bleeding events would occur per year. Aspirin did not affect the risk of death overall or of death due to coronary heart disease. It also had no effect on the risk of stroke. The researchers concluded that taking aspirin for primary prevention was likely to have only a small effect on the risk of serious vascular events, and this would be at least partly offset by a small increase in the risk of serious bleeds. Behind the Headlines covered this meta-analysis on aspirin use in an earlier article.
- One meta-analysis looked at aspirin for primary prevention in men and women separately. It concluded that treatment with aspirin for an average of 6.4 years prevented an average risk of about three cardiovascular events per 1,000 women and four events per 1,000 men. This was offset by an extra 2.5 major bleeding events per 1,000 women and three major bleeding events per 1,000 men.
- Two RCTs looked at aspirin for primary prevention in people with diabetes. One found no reduction in death from coronary heart disease or stroke and the other found no difference in events related to atherosclerosis (hardening of the arteries).
How did the researchers interpret the results?
The article concludes, “the currently available evidence does not justify the routine use of low-dose aspirin for the primary prevention of CVD [cardiovascular disease] in apparently healthy individuals, including those with elevated blood pressure or diabetes; this is because of the potential risk of serious bleeds and lack of effect on mortality.”
This article represents the considered judgment of the DTB based on the existing research evidence and expert opinion. Although steps would have been taken to identify and include the most relevant evidence, some relevant studies may have been missed.
The question of whether apparently healthy people should take aspirin as a preventative measure is difficult to answer due to the fine balance between benefits and risks.
Treatment guidelines (such as those issued by NICE) are produced based on the best evidence available at the time. These guidelines are revised as new evidence becomes available, and when they are next updated they could potentially come to similar conclusions as those reached in this review.
Until then, doctors will continue to make recommendations about taking aspirin by weighing up the balance of benefits and risks for individual cases.