Aspirin to Prevent Recurrent Venous Thromboembolism

Taken together, two trials suggest that aspirin is moderately effective.

In the recent Italian WARFASA trial, aspirin lowered the incidence of recurrent venous thromboembolism (VTE) after first unprovoked VTE events (JW Gen Med May 24 2012). Now, in an international study (ASPIRE), investigators have addressed the same issue in 822 adults who completed 3 to 12 months of standard anticoagulation therapy for unprovoked VTE (42% with pulmonary embolism, 57% with proximal deep venous thrombosis only). Patients then were randomized to receive either 100 mg of aspirin or placebo daily. During average follow-up of 3 years, the following outcomes were noted:

• In the intent-to-treat analysis, the annual rate of recurrent VTE (the primary outcome) was 6.5% in the placebo group and 4.8% in the aspirin group (P=0.09).
• The annual rate of a secondary outcome — a composite of VTE events, myocardial infarction, stroke, or cardiovascular death — was 8.0% in the placebo group and 5.2% in the aspirin group (P=0.01).
• Major bleeding occurred in six placebo recipients and eight aspirin recipients.
• All-cause mortality was 4% in both groups.

Comment: After completing initial courses of anticoagulation, patients with unprovoked VTE are at high risk for recurrence. Indefinite continuation of warfarin lowers that risk substantially but confers considerable ongoing bleeding risk. Aspirin offers a reasonable compromise for such patients. In ASPIRE, a reduction in the VTE endpoint with aspirin didn't quite reach statistical significance, but a combined venous–arterial endpoint did. Because the ASPIRE and WARFASA trials were nearly identical, the two research teams planned prospectively to pool their results. The pooled results appear in this report: Aspirin lowered risk for recurrent VTE by 32% (P=0.007) and lowered risk for combined vascular events (venous and arterial) by 34% (P=0.002) without significantly raising risk for major bleeding.
— Allan S. Brett, MD
Published in Journal Watch General Medicine November 4, 2012
CITATION:
Brighton TA et al. Low-dose aspirin for preventing recurrent venous thromboembolism. N Engl J Med 2012 Nov 4; [e-pub ahead of print]. [Link to free full-text NEJM article PDF | Medline® abstract]