Oral anticoagulation strategies after a first idiopathic venous thromboembolic event

PURPOSE: The optimal duration and intensity of warfarin therapy after a first idiopathic venous thromboembolic event are uncertain. We used decision analysis to evaluate clinical and economic outcomes of different anticoagulation strategies with warfarin. METHODS: We built a Markov model to assess 6 strategies to treat 40- to 80-year-old men and women after their first idiopathic venous thromboembolic event: 3-month, 6-month, 12-month, 24month, and unlimited-duration conventional-intensity anticoagulation (International Normalized Ratio, 2-3) and unlimited-duration low-intensity anticoagulation (international Normalized Ratio, 1.5-2). The model incorporated age- and sex-specific clinical parameters, utilities, and costs. Using a societal perspective, we compared strategies based on quality-adjusted life-years (QALYs), lifetime costs, and incremental cost-effectiveness ratios. RESULTS: In our baseline analysis, incremental cost-effectiveness ratios were lower in younger patients and in men, reflecting the higher bleeding risk at older ages, and the lower risk of recurrence among women. Based on a willingness-to-pay of <$50 000/QALY, the 24-month strategy was most cost-effective in 40-year-old men ($48 805/QALY), while the 6-month strategy was preferred in 40-year-old women ($35 977/QALY) and 60-year-old men ($29 878/QALY). In patients aged >= 80 years, 3-month anticoagulation was less costly and more effective than other strategies. Cost-effectiveness results were influenced by the risks associated with recurrent venous thromboembolism, the major bleeding risk of conventional-intensity anticoagulation and the disutility of taking warfarin. CONCLUSION: Longer initial conventional-intensity anticoagulation is cost-effective in younger patients while 3 months of anticoagulation is preferred in elderly patients. Patient age, sex, clinical factors, and patient preferences should be incorporated into medical decision making when selecting an appropriate anticoagulation strategy. (c) 2005 Elsevier Inc. All rights reserved.