Aspirin didn't reduce recurrent VTE but did reduce major vascular events

Low-dose aspirin may have therapeutic benefit for patients who have completed initial anticoagulant therapy for an unprovoked venous thromboembolism (VTE) even though the rate of recurrent VTE was not significantly reduced in a recent study.

The trial included more than 800 patients who had a first unprovoked VTE and completed treatment with heparin followed by warfarin for at least six weeks (most for at least three months). They were randomized to either 100 mg of aspirin per day or placebo for up to four years. Results were published online by the New England Journal of Medicine on Nov. 4.

The rate of recurrent VTE was lower in the aspirin group, but the difference was not statistically significant (6.5% per year on placebo vs. 4.8% per year on aspirin; hazard ratio, 0.74; 95% CI, 0.52 to 1.05; P=0.09). Aspirin did significantly decrease a prespecified composite outcome: The rate of VTE, myocardial infarction, stroke or cardiovascular death was 5.2% per year with aspirin compared to 8.0% on placebo (hazard ratio, 0.66; P=0.01). The groups had similar rates of major or clinically relevant nonmajor bleeding episodes (0.6% per year with placebo vs. 1.1% per year with aspirin; P=0.22).

The authors concluded that although aspirin didn't significantly reduce VTE, it did significantly reduce major vascular events, providing a net clinical benefit. They noted that recruitment and retention of fewer patients than planned led to the trial being underpowered to detect an effect on VTE. When the results were combined with those of another recent, similar trial, a statistically significant reduction in VTE of 32% was found (P=0.007).

Based on the findings of the current study, the authors calculated that for every 1,000 patients treated with aspirin for a year, there would be 17 fewer VTEs, 28 fewer major thrombotic events and five additional nonfatal bleeding episodes. Aspirin is less effective than warfarin but may be more attractive to patients for long-term use, they concluded.

An accompanying editorial agreed, noting that in addition to the lesser expense and freedom from monitoring, aspirin is more easily reversible and provides extra protection against arterial thrombosis. It seems to be a “reasonable option” for patients who have completed initial anticoagulation, the editorialist concluded.