Prophylactic aspirin reduces the risk of non-fatal myocardial infarction in people without cardiovascular disease but does not reduce cardiovascular or cancer mortality, and any benefit is offset by the raised risk of bleeding events, a large meta-analysis looking at aspirin in primary prevention has shown.
The authors argue, in the Archives of Internal Medicine, that guidelines currently recommending use of aspirin in primary prevention should be reviewed in the light of their findings, adding that routine use of aspirin for primary prevention “is not warranted and that treatment decisions need to be considered on a case by case basis”.
Previous meta-analyses have shown modest benefits of aspirin for the primary prevention of cardiovascular disease, but it has been unclear to what extent these were offset by clinically important bleeding episodes, the researchers, from St George’s, University of London, write.
Emerging data from primary and secondary prevention trials have indicated significant reductions in cancer mortality in people taking prophylactic aspirin.
To look at this further, the researchers carried out a meta-analysis of published randomised, placebo controlled trials investigating aspirin in at least 1000 participants without cardiovascular disease, including three recent studies.
They identified nine original trials that reported on cardiovascular or cancer outcomes, with a total of nearly 103,000 participants.
Their analysis showed that aspirin reduced the total number of cardiovascular events by 10 per cent over a mean follow-up of six years; 2,107 events in 52,145 people taking aspirin and 2,171 events in 50,476 in the placebo group.
This reduction was driven primarily by fewer non-fatal myocardial infarctions.
However there was no significant reduction in cardiovascular deaths (674 in 52, 145 versus 611 in 50,476) or cancer mortality (750 in 49,919 versus 762 in 48,207), and the risk of non-trivial bleeding events was 31 per cent higher among participants taking aspirin; 5,337 cases in 50,868 versus 4,712 in 49,208.
The lead author of the meta-analysis, Dr Rao Seshasai, Clinical Lecturer in Preventive Cardiology at St George’s, said that there was no question about the evidence for aspirin in preventing cardiovascular events in people with established cardiovascular disease.
“However, the benefits of aspirin in those individuals not known to have these conditions are far more modest than previously believed, and in fact aspirin treatment may potentially result in considerable harm due to major bleeding,” he said.
“Hence, it would be worthwhile to review the existing recommendations, such as the US Preventive Services Task Force guidelines and the Joint British Societies’ guidelines, for the use of this agent in low risk populations and consider aspirin treatment more selectively on a case by case basis.”
He added: “There is an enormous interest in understanding the role of aspirin in cancer prevention. No evidence of benefit was found in the studies reviewed, but more research is needed given these were only of six years in duration.”
In an editorial accompanying the meta-analysis, Professor Samia Mora, Assistant Professor of Medicine at Brigham and Women’s Hospital, Harvard Medical School, US, said that the new data argue against the routine use of aspirin for primary prevention.
She suggested that the benefit to risk ratio for aspirin should be weighed carefully for people with no prior cardiovascular disease.
“As the current guidelines recommend, it is reasonable to consider using aspirin for primary prevention in higher risk individuals without known CVD if they are deemed to have a greater benefit to risk ratio,” she said.
Image courtesy of Schjelderup, Flickr Creative Commons
