I had thought that aspirin was for the most part not considered very useful as a medication that could prevent venous thrombosis but had an important role in preventing arterial thrombosis .Now we have evidence from a clinical trial that aspirin may be useful in prevention of venous thrombosis.See here. As the discussion section of the NEJM article (linked below) indicated there had been previous published data suggesting aspirin's value in venous thrombosis prevention but for some reason aspirin never seemed to achieve a reputation as a useful venous thrombosis prevention.
The trial,WARFASA,studied patients who had received 6-18 months of standard therapy for venous thromboembolism (VTE) .The treatment group received 100 mg aspirin per day and the recurrence of VTE was significantly less in the treatment group. The recurrence rate was 11.2 events/years in the control group versus 6.6 in the aspirin group with one instance of major bleeding in each group. The recurrence rate seen in the control group is compatible with the usually quoted 10% per year recurrence in patient with unprovoked VTE after anticoagulation therapy is discontinued. See here for the study published in NEJM.
The study was done in Italy where the 100 mg aspirin tablet is available.As far as I can tell in the US,we have only a 80 mg. aspirin.and the regular strength aspirin.
Of course, aspirin is not the new warfarin but might it have a role in the longer term treatment of a patient with unprovoked VTE? Dr. Stephen Moll, a hematologist with special interest in thrombosis offers his take on this study and how he plans to use aspirin in some of his VTE patients. See here for the commentary on his blog ClotConnect.
Another similar trial is underway ( the ASPIRE trial ) is scheduled to offer some results later in 2012 and hopefully will be able to offer confirmation of this rather small trial.
Interestingly,the 9th edition of the ACCP clinical guidelines on antithrombolic therapy and prevention recommends against the use of aspirin in the prevention of VTE in long haul flights.See here.