Stephan Moll, MD writes… An important study was published on May 23rd, 2012 in the New England Journal of Medicine [ref 1], showing that aspirin decreases the risk of recurrent clots (DVT and PE) in patients who have had a previous unprovoked (= idiopathic) clot and who have completed 6 to 18 months of blood thinner therapy. Aspirin did not lead to 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 venous thromboembolism (also referred to as VTE – a term that encompasses DVT and PE). However, aspirin’s protective effect has only been mild. The 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 for a little more than 2 years. This was a double-blind study.
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. Major bleeding and clinically relevant non-major bleeding occurred was similar in both treatment groups.
Aspirin reduces the risk of recurrent clots in patients with unprovoked venous thromboembolism, once they have finished standard length of blood thinner therapy, with no apparent increase in the risk of major bleeding.
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 when they stop warfarin, that it is worthwhile to take aspirin long-term.
- What dose do I recommend? In the U.S., where the 100 mg tablet size studied in this NEJM study are not available I tell patients to take either a baby aspirin (81 mg) or an adult aspirin (325 mg) – typically I recommend the 81 mg size.
- Would I recommend that patients who are on long-term warfarin, Pradaxa or Xarelto, now stop their blood thinner 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 blood thinners.
- Would I recommend aspirin therapy in women who had a VTE associated with contraceptive pills, rings, or patches and have now come off blood thinners? Yes. However, such women were not included in the study published.
Becattini C et al. Aspirin for preventing the recurrence of venous thromboembolism. N Engl J Med 2012(May 24th);366:1959-1967.
Disclosure: I have no conflict of interest relevant to this post.
Last updated: Nov 9th, 2012