OPTIMAL DURATION OF ORAL ANTICOAGULANT-THERAPY - A RANDOMIZED TRIAL COMPARING 4 WEEKS WITH 3 MONTHS OF WARFARIN IN PATIENTS WITH PROXIMAL DEEP-VEIN THROMBOSIS

The optimal duration of oral anticoagulant therapy for patients with a cute proximal deep vein thrombosis (DVT) is uncertain. Based on the hy pothesis that a normal impedance plethysmogram (IPG) following DVT def ines a group of patients at low risk of recurrent venous thromboemboli sm (VTE), a trial was conducted to evaluate the efficacy of only four weeks of warfarin. Patients with venographically confirmed acute proxi mal DVT who had received four weeks of warfarin after initial heparin and whose four week IPG was normal were allocated to either continue w arfarin (targeted International Normalized Ratio 2.0 to 3.0) for a fur ther eight weeks or receive placebo. Patients with an abnormal four we ek IPG received warfarin for a further eight weeks. Based on clinical characteristics at the time of the qualifying thrombosis, all patients were classified as having either continuing or transient risk factors for recurrent VTE. During the eight weeks following randomization, ni ne (8.6%) of the 105 placebo patients developed recurrent VTE compared to one (0.9%) of the 109 warfarin patients, P = 0.009. Over the entir e 11 months of follow-up, 12 placebo patients developed recurrence com pared to seven warfarin patients, P = 0.3. Nineteen of the 192 patient s with an abnormal four week IPG experienced recurrence during the nin e months after discontinuing warfarin. In the 301 patients who receive d three months of warfarin in the randomized trial or in the cohort st udy, all 26 recurrent events were in the 212 patients with continuing risk factors. In conclusion, an IPG four weeks after proximal DVT is n ot a useful predictor for recurrent VTE; whereas the presence of conti nuing risk factors is a very strong predictor. Four weeks of oral anti coagulants may be all that is required in patients without continuing risk factors, Patients with continuing risk factors may require more t han three months of oral anticoagulants.