To some degree it does, but it is by far not as effective as warfarin or other anticoagulants. However, a very noteworthy study was presented today (Dec 12, 2012) at the annual American Society of Hematology meeting [ref 1]. It showed that aspirin was much more effective than placebo in preventing venous thromboembolism (VTE) in patients with a history of unprovoked VTE. This is thrilling news. However, the study needs to be replicated and results confirmed in a second study.
Aspirin and DVT and PE: Previous data
There has been some evidence over the years that aspirin protects some against VTE [ref 2,3]. However, the effect observed has been mild. Therefore, the conclusion has been for years that aspirin does not in any major way protect from VTE. This is in keeping with the concept that venous clots are made up mostly of fibrin and that platelets contribute little to venous thrombosis.
The new study
The study presented today at the annual meeting of the American Society of Hematology (WARFASA study) investigated patients with a history of unprovoked VTE. They were enrolled after they had been treated for their VTE with warfarin for 6-18 months and then randomized to aspirin or placebo. It was a double-blind study. Patients were followed for an average of 2 years. Primary endpoints were symptomatic VTE and fatal PE. The aspirin dose used was 100 mg a day. 403 patients were enrolled, 205 of whom received aspirin, 198 placebo. The study found that aspirin was effective in preventing some clots: recurrent VTE occurred in 11.0 % of patients treated with placebo and in 5.9 % on aspirin. This was a 40 % risk reduction. Major bleeding and clinically relevant non-major bleeding occurred similarly in both treatment groups. Thus, the appropriate conclusion that aspirin was safe and effective in preventing some VTEs. A few limitations of this new study need to be mentioned: It has only been presented and published as an abstract, not yet in a peer-reviewed journal; and a follow-up study needs to be done to see whether the results can be confirmed.
The study findings are remarkable. Aspirin can prevent some DVTs and PEs, without an increase in bleeding risk.
- Does this study change my clinical practice? Yes. I used to tell patients who came off warfarin after treatment for an appropriate length of time (often 3-6 months) that there was no strong reason to take aspirin. I will now tell them that, once they stop warfarin, it is worthwhile to take aspirin long-term.
- What dose will I recommend? I will tell the patient that here in the U.S. where we do not have 100 mg tablet sizes, either a baby aspirin (81 mg) or an adult aspirin (325 mg) would be appropriate.
- Would I recommend that patients who are on long-term warfarin now stop warfarin and switch to aspirin instead? No. Clearly not. Warfarin is much more effective than aspirin. Aspirin is not a replacement for warfarin.
- Becattini C et al. Aspirin for the prevention of recurrence of venous thromboembolism. The WARFASA study. Blood 2011;118:251(abstract 543).
- Antiplatelet Trialists’ Collaboration: Collaborative overview of randomized trials of antiplatelet therapy – III. Reduction in venous thrombosis and pulmonary embolism by antiplatelet prophylaxis among surgical and medical patients. BMJ 1994;308:235-246.
- Prevention of pulmonary embolism and deep vein thrombosis with low dose aspirin: Pulmonary Embolism Prevention (PEP) trial. Lancet 2000,Apr 15;355(9212):1295-302.
Disclosure: I have no conflict of interest relevant to this post.
Last updated: Dec 12th, 2011