An aspirin a day can keep VTE at bay

Venous thromboembolism (VTE) risks in patients taking aspirin were significantly reduced over nontreatment in a study published online Aug. 25 in Circulation.

The INSPIRE (International Collaboration of Aspirin Trials for Recurrent Venous Thromboembolism) study recruited it’s cohorts from two other studies: WARFASA (Warfarin and Aspirin) and ASPIRE (Aspirin to Prevent Recurrent Venous Thromboembolism). John Simes, MD, of the National Health and Medical Research Council Clinical Trials Centre at the University of Sydney, and colleagues explored treatment effects in these patients for aspirin vs. placebo on recurrent VTE and other risks, such as bleeding, MI, stroke or cardiovascular-related death.

Over the course of the next two to four years, Simes et al followed up with patients. Venous thromboembolism occurred in 18.4 percent of placebo patients. In the aspirin group, that number was down to 13.1 percent. According to Simes et al, this relates to a 32 percent relative reduction in the occurrence of VTE among aspirin patients. There were two fatalities in each group attributable to VTE.

Pulmonary embolism was reduced by 34 percent by aspirin use with or without symptomatic deep vein thrombosis, while deep vein thrombosis without symptomatic pulmonary embolism was also reduced by 34 percent with aspirin use.

Major cardiovascular events occurred at a rate of 5.7 percent per year with aspirin while the placebo group experienced a rate of 8.7 percent per year. Bleed rate per year was low and was not considered to be significantly different between the placebo (0.7 percent) and aspirin (1.1 percent) groups by the research team.

Simes et al noted that the highest reduction in potential recurrent events occurred in the first year with aspirin use, bringing the number of events down to 5.4 percent from 11 percent.

Over time, however, treatment adherence dropped and while those taking aspirin were more likely to continue treatment, patients fell away from aspirin at a rate of 11.4 percent per year against the placebo’s 13.4 percent per year. The research team wrote that they were concerned that the falling adherence may have muddled the true effect of treatment over the long term.

However, Simes et al were optimistic about the benefits of the study. “If a million patients worldwide could be treated with aspirin each year, a hundred thousand events might be prevented with a minimal increase in bleeding (about 1 extra major bleed for every 25 VTEs prevented) and with a treatment that would be cost saving (the costs of treating subsequent VTEs avoided would outweigh the cost of aspirin),” they wrote.

Thomas W. Wakefield, MD, and colleagues from the University of Michigan in Ann Arbor wrote in an editorial that this study offers an interesting look at aspirin therapy, but also invites a new set of questions in the field of clot treatment. While they could see the benefit for patients with moderate risk, Wakefield et al asked if there was an optimal length of time that aspirin therapy would work for these patients. They also wondered if patients with low risk for recurrence should be prescribed aspirin as well and what other VTE patients also would respond well to aspirin therapy.

Simes et al wrote that their analysis is clear evidence of a 40 percent reduction risk of recurrent VTE events and was safe and effective. They suggested considering aspirin for patients for whom newer oral anticoagulants or vitamin K antagonists were not recommended.