HealthDay News — Aspirin did not reduce recurrent venous thromboembolism (VTE) in patients with a first unprovoked event who completed initial anticoagulant therapy, but it did provide significant secondary cardioprotective benefits, findings from the ASPIRE trial indicate.

Recurrent annual VTE rates for patients who were evenly randomized and followed for a mean 37 months were  4.8% among those assigned to 100 mg daily aspirin vs. 6.5% in patients assigned to placebo (hazard ratio for aspirin=0.74; 95% CI: 0.52-1.05; P=0.09), Timothy Brighton, MB, of the Prince of Wales Hospital in Adelaide, Australia, and colleagues found.

After adjusting for baseline differences, aspirin came close but did not reach statistical significance for reducing recurrent VTE rates (HR=0.72; 95% CI: 0.51-1.01; P=0.06), the researchers reported at the American Heart Associations 2012 Scientific Session.

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Despite these findings, aspirin did significantly reduce major vascular events (5.2% vs. 8%), defined as a composite of VTE, myocardial infarction, stroke or cardiovascular death (HR=0.66; 95% CI: 0.48-0.92; P=0.01).

“These results substantiate earlier evidence of a therapeutic benefit of aspirin when it is given to patients after initial anticoagulant therapy for a first episode of unprovoked venous thromboembolism,” the researchers said.

The rates of major or clinically relevant non-major bleeding episodes or serious adverse events were not significantly different between the groups — 14 for aspirin vs. 8 for placebo (HR=1.73; 95% CI: 0.72-4.11; P=0.22).

Presentation of the study results at AHA 2012 coincided with it’s publication in New England Journal of Medicine.

In an accompanying editorial, Theodore Warkentin, MD, of McMaster University in Ontario, Canada, pointed out that a similar trial called WARFASA did show significant benefits for aspirin regarding recurrent VTE (6.6% vs. 11.2% per year; HR=0.58; 95% CI: 0.36-0.93; P=0.02).

When data from ASPIRE and WARFASA were pooled, there was a 32% reduction in VTE recurrence rates (HR= 0.68; 95% CI: 0.51-0.90; P=0.007) and a 34% reduction in the rate of major vascular events (HR=0.66; 95% CI: 0.51-0.86; P=0.002).

However, before prescribing aspirin for patients who have had an acute unprovoked venous thromboembolism Warkentin advises clinicians to treat patients with effective anticoagulation for at least 3 months, to avoid the high risk of early recurrence.

“Aspirin is inexpensive, does not require monitoring (in contrast to warfarin), and does not accumulate in patients with renal insufficiency (in contrast to dabigatran [Pradaxa] and rivaroxaban [Xarelto]); in addition, if major bleeding occurs or the patient requires urgent surgery, the antiplatelet effects of aspirin can be reversed with transfusion of platelets,” Warkentin added.


  1. Brighton TA et al. N Engl J Med. 2012; doi: 10.1056/NEJMoa1210384.
  2. Warkentin TD. N Engl J Med. 2012; doi: 10.1056/NEJMe1211480.