Risks of long-term oral anticoagulation in a non-trial medical environment

Randomised controlled trials have shown that anticoagulation with warfarin reduces the risk of stroke in patients with atrial fibrillation by two thirds. However there is concern as to whether the rate of anticoagulant-related haemorrhage seen in these trials would be reproduced in a non-trial setting. Four hundred and ten consecutive patients attending a special anticoagulation clinic over one year were asked to complete a questionnaire concerning their warfarin treatment. The total number of years on warfarin was 2870. Of the 410 patients, 59 (14%) admitted to 88 bleeding episodes while on warfarin. Of these bleeding problems, 36/88 (41%) required admission to hospital or to casualty for treatment and 52/88 (59%) required only a lowering or temporary cessation of warfarin therapy. The calculated annual non-fatal bleeding rate of 3% in this survey is identical to that reported from the Copenhagen AFASAK trial. Similarly the 1.3% annual rate of major bleeding requiring attendance at hospital is identical to that in the Stroke Prevention in Non-Rheumatic Atrial Fibrillation trial. The results of this study suggest that oral anticoagulation is as safe in an ordinary medical setting as in a closely supervised trial setting.