Aspirin Prevents Recurrent Unprovoked Venous Thromboembolism

Aspirin is probably less effective –– but safer –– than warfarin.
Patients with unprovoked venous thromboembolism (VTE) face a dilemma: Recurrent VTE is common after warfarin anticoagulation is stopped, but the cumulative incidence of serious bleeding is high when patients continue warfarin therapy indefinitely. This difficult tradeoff provides an impetus to see whether aspirin is a suitable alternative for such patients.
Italian researchers identified 403 patients with a first symptomatic VTE event that was unprovoked (i.e., not associated with standard VTE risk factors); 63% had proximal deep venous thrombosis, and 37% had pulmonary embolism. After 6 to 18 months of treatment with a vitamin K antagonist, patients were randomized to either aspirin (100 mg daily) or placebo for 2 years.
The incidence of recurrent VTE was significantly lower in the aspirin group than in the placebo group (6.6% vs. 11.2% annually; P=0.02). The frequency of bleeding events was identical in the two groups (1 major bleed and 3 nonmajor bleeds). Aspirin afforded protection both to patients whose index event was deep venous thrombosis and to those whose index event was pulmonary embolism.
Comment: For patients with unprovoked VTE, this trial provides persuasive evidence that aspirin reduces the incidence of recurrent events after conventional warfarin therapy. Aspirin is less effective than warfarin, but bleeding risks are lower with aspirin. Newer oral anticoagulants (e.g., dabigatran and rivaroxaban) have also been studied as extended maintenance therapies for patients with VTE, but are not yet FDA-approved for this purpose.
— Allan S. Brett, MD
Published in Journal Watch General Medicine May 24, 2012