Aspirin given for up to 2 years after initial anticoagulant treatment reduces the risk of venous thromboembolism recurrence without increasing risk of major bleeding.

Context Venous thromboembolism, which encompasses deep vein thrombosis and pulmonary embolism, is a relatively common disorder with an incidence in western countries of around 1/1000 per annum. Events are categorised as either provoked, that is occurring in the context of a known temporary risk factor such as surgery, or unprovoked, that is occurring without an associated known risk factor. There is a general consensus that provoked events have a low risk of recurrence and should be treated for a finite period of anticoagulation. However, unprovoked events have a higher rate of recurrence (8–10% per annum) following discontinuation of anticoagulation. This high rate of recurrence has prompted debate around the optimal duration of anticoagulant therapy for this group of patients. The dilemma is that prolonged anticoagulation reduces the risk of recurrent thrombosis while increasing the risk of bleeding events including potentially fatal intracranial bleeding. Efforts to resolve this dilemma have two main approaches. The first is to identify patient features and markers that predict risk of recurrence. The second is to continue thromboprophylaxis using less intense anticoagulation in anticipation that this might confer a benefit in terms of reducing thrombosis recurrence without significantly increasing the risk of bleeding. Previous investigation into such an approach using low-intensity anticoagulation with warfarin (aiming for an international normalised ratio of 1.5–2) showed that although there appeared to be a benefit for low intensity warfarin it was inferior to conventional intensity warfarin with no reduction in major bleeding. 4