Aspirin may be a promising alternative for those who can’t take long-term anticoagulant drugs that prevent clots from reoccurring in the veins, according to new research in the American Heart Association journal Circulation.

In a combined analysis of two similar independent studies, 1,224 patients who received 100 mg of aspirin a day to treat blood clots were monitored for at least two years. In the International Collaboration of Aspirin Trials for Recurrent Venous Thromboembolism or INSPIRE analysis, researchers found that aspirin reduced the risk of recurring blood clots by up to 42 percent.

Venous thromboembolism (VTE) are blood clots in veins. The blood clot can occur in the deep veins of the legs (deep vein thrombosis) and can break apart and travel to the lungs, where they block off arteries in the lungs (Pulmonary embolism).

According to researchers, without treatment, people who have blood clots in their veins with no obvious cause have on average a 10 percent risk of another clot within the first year and a 5 percent risk per year thereafter.

“The treatment is warfarin or a newer anticoagulant usually given for at least six to 12 months to prevent a further blood clot,” said John Simes, M.D., lead author of study and director of the National Health and Medical Research Council Clinical Trials Centre and professor at the University of Sydney in Australia. “However, these people continue to be at risk.”

Co-author Cecilia Becattini, M.D., added, “Aspirin does not require laboratory monitoring, and is associated with about a 10-fold lower incidence of bleeding compared with oral anticoagulants. We are convinced that it will be an alternative for extended prevention of venous thromboembolism after 6–12 months of anticoagulant treatment.”

Although the study yielded clear results, researchers advise patients to talk to their doctor about taking aspirin after stopping treatment with anticoagulants.

“It is not recommended that aspirin be given instead of anticoagulant therapy, but rather be given to patients who are stopping anticoagulant therapy or for whom such treatments are considered unsuitable,” Simes said.

“Although less effective, aspirin is inexpensive, easily obtainable, safe and familiar to patients and clinicians worldwide. If cost is the main consideration, aspirin is a particularly useful therapy. The costs of treating future thromboembolic events is greater than the cost of the preventive treatment.”

Other co-authors are Giancarlo Agnelli, M.D.; John W. Eikelboom, M.B., B.S.; Adrienne C. Kirby, M.Sc.; Rebecca Mister, M.Sc.; Paolo Prandoni, M.D.; and Timothy A. Brighton, M.B., B.S. Author disclosures and funding information are on the manuscript.

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Statements and conclusions of study authors published in American Heart Association scientific journals are solely those of the study authors and do not necessarily reflect the association’s policy or position. The association makes no representation or guarantee as to their accuracy or reliability. The association receives funding primarily from individuals; foundations and corporations (including pharmaceutical, device manufacturers and other companies) also make donations and fund specific association programs and events. The association has strict policies to prevent these relationships from influencing the science content.

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