The use of aspirin in people with no history of relevant disease can reduce non-fatal MIs by approximately one-fifth, but it also can increase the risk of internal bleeding by around one-third in this same population. Thus, its long-term use for primary prevention is uncertain since its risks and benefits could potentially cancel each other out, according to a study in the May 29 issue of the Lancet.
However, the authors noted that for secondary prevention, among those patients who already have occlusive vascular disease, aspirin's benefits generally outweigh its risks.
In the U.K. Medical Research Council funded study, Colin Baigent, PhD, clinical trial service unit and epidemiological studies unit at the University of Oxford in England, and colleagues did an individual patient meta-analysis of serious vascular events (MI, stroke or vascular death) and major bleeds in six primary prevention trials, involving 95,000 people at low-average risk, and 16 secondary prevention trials, involving 17,000 people at high risk. The studies compared long-term aspirin use with control.
The researchers found that in the primary prevention trials, aspirin reduced the already small risk of serious vascular events (stroke, MI, vascular death) by 12 percent, mainly due to the reduction in non-fatal heart attack mentioned above. There was no significant difference in stroke or in vascular mortality, but the small risk of internal bleeds increased by around a third in those given aspirin.
In the secondary prevention studies, where people had already had a stroke or heart attack and were at substantial risk of recurrence, aspirin reduced the risk of serious vascular events by about a fifth, and this benefit clearly outweighed any small extra risk of bleeding, according to the authors. In both sets of trials, the proportional reductions in vascular events were similar for men and women.
The authors concluded that the "currently available trial results...do not seem to justify general guidelines advocating the routine use of aspirin in all healthy individuals above a moderate level of risk for coronary heart disease."
"Drug safety really matters when making recommendations for tens of millions of healthy people," Baigent said. "We don't have good evidence that, for healthy people, the benefits of long-term aspirin exceed the risks by an appropriate margin. If effectiveness is uncertain, then cost-effectiveness calculations are irrelevant."
In an accompanying commentary, Ale Algra, PhD, and Jacoba P. Greving, MD, University Medical Centre Utrecht in Utrecht, Netherlands, used a cost-effectiveness model to create a table showing which populations might or might not benefit from aspirin in primary prevention--which shows that, in most cases, it is not justified.
"Patients might not wish to be medicalized--such considerations are important in the decision to take aspirin or not. Whether statins should be preferred above aspirin is a different and difficult question that needs careful consideration too. Apart from drug treatment, one must not forget the importance of lifestyle changes, such as cessation of smoking, healthy diet, and regular exercise," Algra and Greving concluded.