Articles16 October 2007
A Randomized Trial
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    Short-term aspirin therapy can lower the risk for venous thromboembolism (VTE) in high-risk patients, but whether the long-term use of low-dose aspirin reduces risk in healthy adults is uncertain.


    To test the efficacy of long-term aspirin therapy for preventing VTE.


    Secondary analysis of a 10-year randomized, double-blind, placebo-controlled trial.


    U.S. female health care professionals in the Women's Health Study.


    39 876 initially healthy women age 45 years or older (26 779 gave blood samples that were evaluated for factor V Leiden, G20210A prothrombin, and MTHFR 677C>T polymorphisms).


    Documented VTE (deep venous thrombosis or pulmonary embolism) and unprovoked VTE (no recent surgery, trauma, or cancer diagnosis) were prospectively evaluated, secondary end points.


    Aspirin, 100 mg, or placebo on alternate days.


    Venous thromboembolism occurred in 482 women during follow-up, an incidence higher than that of myocardial infarction and nearly equal to that of stroke. The incidence of VTE (per 1000 person-years) was 1.18 among women randomly assigned to active aspirin, compared with 1.25 among women randomly assigned to placebo (relative hazard, 0.95 [95% CI, 0.79 to 1.13]; rate difference, −0.06 [CI, −0.28 to 0.16]). For unprovoked VTE, the relative hazard was 0.90 (CI, 0.70 to 1.16) and the rate difference was −0.06 (CI, −0.21 to 0.10). Relative hazards associated with aspirin use in higher-risk subgroups were 0.83 (CI, 0.50 to 1.39) among women with either factor V Leiden or the prothrombin mutation and 1.36 (CI, 0.77 to 2.41) among those with a history of VTE.


    Venous thromboembolism was a secondary end point in the Women's Health Study.


    These data suggest that long-term, low-dose aspirin treatment has little effect on the prevention of VTE in initially healthy women. registration number: NCT00000479.


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