Effect of low-dose aspirin on the occurrence of venous thromboembolism: a randomized trial.
BACKGROUND
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.


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


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


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


METHODS
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).


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


METHODS
Aspirin, 100 mg, or placebo on alternate days.


RESULTS
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.


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


CONCLUSIONS
These data suggest that long-term, low-dose aspirin treatment has little effect on the prevention of VTE in initially healthy women. ClinicalTrials.gov registration number: NCT00000479.
Glynn
Robert J
RJ
Brigham and Women's Hospital, Harvard Medical School, and Harvard School of Public Health, Boston, Massachusetts 02215, USA. rglynn@rics.bwh.harvard.edu .
Ridker
Paul M
PM
Goldhaber
Samuel Z
SZ
Buring
Julie E
JE
D001241:Aspirin / Q000008:administration & dosage* / Q000009:adverse effects; D004311:Double-Blind Method; D004334:Drug Administration Schedule; D005260:Female; D005343:Fibrinolytic Agents / Q000008:administration & dosage* / Q000009:adverse effects; D005500:Follow-Up Studies; D006470:Hemorrhage / Q000139:chemically induced; D006801:Humans; D015994:Incidence; D008875:Middle Aged; D010437:Peptic Ulcer / Q000139:chemically induced; D011446:Prospective Studies; D012307:Risk Factors; D013923:Thromboembolism / Q000453:epidemiology / Q000517:prevention & control*; D020246:Venous Thrombosis / Q000453:epidemiology / Q000517:prevention & control*
D005343:Fibrinolytic Agents; D001241:Aspirin