Efficacy and Safety of Warfarin for the Treatment of Venous Thromboembolism　― A Multicenter Prospective Observational Cohort Study in Japan (AKAFUJI Study)

Background: A large-scale prospective study of the efficacy and safety of warfarin for the treatment of venous thromboembolism (VTE) has not been conducted in Japan. Therefore, we conducted a real-world prospective multicenter observational cohort study (AKAFUJI Study; UMIN000014132) to investigate the efficacy and safety of warfarin for VTE.Methods and Results: Between May 2014 and March 2017, 352 patients (mean [±SD] age 67.7±14.8 years; 57% female) with acute symptomatic/asymptomatic VTE were enrolled; 284 were treated with warfarin. The cumulative incidence of recurrent symptomatic VTE was higher in patients without warfarin than in those treated with warfarin (8.7 vs. 2.2 per 100 person-years, respectively; P=0.018). The cumulative incidence of bleeding complications was not significantly different between the 2 groups. The mean prothrombin time-international normalized ratio (PT-INR) during warfarin on-treatment was 2.5 in 6 patients. The incidence of bleeding complications was significantly higher in patients with PT-INR >2.5, whereas the incidence of recurrent VTE was not significantly different between the 3 PT-INR groups. The cumulative incidence of recurrent VTE and bleeding complications did not differ significantly among those in whom VTE was provoked by a transient risk factor, was unprovoked, or was associated with cancer.Conclusions: Warfarin therapy with an appropriate PT-INR according to Japanese guidelines is effective without increasing bleeding complications, regardless of patient characteristics.