Education Blog for Healthcare Professionals

Aspirin Prevents Recurrent DVT and PE – WARFASA Study

Stephan Moll, MD writes… A clinically very relevant study (WARFASA) published today (May 24, 2012) in the New England Journal of Medicine [ref 1] shows that aspirin, 100 mg per day, reduces the risk of recurrent venous thromboembolism (VTE) in patients with unprovoked (= idiopathic) VTE, who have completed 6 to 18 months of anticoagulant therapy, without an apparent increase in risk of major bleeding

Background and Methods

There has been some evidence over the years that aspirin has some protective effective against VTE, but the effect observed had been relatively mild. The WARFASA study published today investigated patients with a history of unprovoked VTE. After patients had been treated routinely with warfarin for 6-18 months, they were enrolled and randomized to aspirin 100 mg /day or placebo and treated in a double-blind design for a median of 2 years. Primary endpoints were symptomatic VTE and fatal PE. Primary safety outcome was major bleeding.


403 patients were enrolled: 205 received aspirin, 197 placebo. Median study period was 26.6 months. VTE recurred in 13.7% of patients treated with aspirin, and in 21.8 % on placebo, i.e. 6.6 % vs. 11.2 % per year (hazard ratio, 0.58; 95 % confidence interval, 0.35 to 0.93). This equals a 40 % risk reduction with aspirin. Major bleeding and clinically relevant non-major bleeding occurred was similar in both treatment groups.


Aspirin reduces the risk of recurrent VTE in patients with unprovoked VTE once they have finished standard length of anticoagulant therapy, with no apparent increase in the risk of major bleeding.

My Perspective

The study findings are remarkable. Aspirin can prevent some DVTs and PEs, with no detectable increase in major bleeding risk. Consequences for my practice:

  • Does this study change my clinical practice? Yes. I used to tell patients who came off warfarin after they had been treated for an appropriate length of time (often 3-6 months), that there was no strong reason to take aspirin. I now tell them that, once they stop warfarin, it is worthwhile to take aspirin long-term.
  • What dose do I recommend? I tell the patient that here in the U.S., where we do not have the100 mg tablet size studied in this NEJM publication, either a baby aspirin (81 mg) or an adult aspirin (325 mg) would be appropriate. I typically recommend the 81 mg size.
  • Would I recommend that patients who are on long-term warfarin, Pradaxa or Xarelto, now stop their anticoagulant and switch to aspirin instead? No. Clearly not. Warfarin is much more effective than aspirin. Aspirin is not a replacement for warfarin. But aspirin is better than nothing if the patient with unprovoked VTE has stopped anticoagulation.
  • Would I recommend aspirin therapy in women who had a VTE associated with contraceptives and have now come off anticoagulation? Yes, even though such women were not included in the study published.



Becattini C et al. Aspirin for preventing the recurrence of venous thromboembolism. 2012(May 24th);366:1959-1967.


Disclosure:  I have no conflict of interest relevant to this post.

Last updated: May 23rd, 2012

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