Quality Assessment of Oral Anticoagulation by Time in Therapeutic Range in Patients with Venous Thromboembolism in Korea

Abstract

Purpose To assess the efficacy and safety of oral anticoagulation with warfarin by time in therapeutic range in patients with venous thromboembolism (VTE) in South Korea. Methods This was a retrospective, single-center study to evaluate patients diagnosed with VTE and managed with adjusted dose of warfarin over two-thirds of follow-up period in Thrombosis Clinic between February 2009 and August 2010. Validated dosing algorithm was used to manage the international normalized ratio (INR). Time in therapeutic range was calculated by Rosendaal method. Results The period of predetermined warfarin interruption for peri-operative management (1 week preoperatively and 3 weeks post-operatively) was censored. It was not analyzed in 34 episodes. Out of 76 patients with VTE, 47 (23 men; mean age 64.9 years) were analyzed. Approximately two-thirds (31/47) of patients were warfarin-naïve. Total number of admissions was 84. Expected duration of anticoagulation was 6 months in 22 patients (47%), 12 months in 1 (2%), and indefinite in 24 (51%). There were various comorbidities, including active malignancy in 7 patients (15%), mycobacterium tuberculosis on rifampicin in 4 (8.5%), chronic kidney disease in 4 (8.5%), and hemorrhagic cerebral infarct in 1 (2%). Overall time in therapeutic range (TTR) was 52.4%. Most proportion of out-of-range was below the therapeutic range (29.5%). There was no thromboembolic complication, although two cases of major bleeding complications were observed. Conclusion The validated dosing algorithm is effective for managing INRs in patients with VTE in Korea. Keywords: Time in therapeutic range, Warfarin, International normalized ratio, Venous thromboembolism