Experiences of a low-intensity anticoagulation regimen for extended secondary prevention of venous thromboembolism.

Extended treatment with vitamin K antagonists for more than 6 months is often used for secondary prevention of venous thromboembolism (VTE) in patients at high or moderate risk for recurrent events. The intensity of anticoagulant therapy is usually maintained at an International Normalized Ratio (INR) of 2-3. An INR of 1.5-2 might also prevent thromboembolic events with less complications of bleeding, but results from randomized trials are not yet available. In a non-prospective, uncontrolled study 40 patients with a history of VTE and an estimated high risk for recurrent events due to several previous events and/or thrombophilic defects were, after a median of 11.5 months on regular intensity anticoagulation (INR 2-3), switched to a low intensity regimen (INR 1.5-2). In six of the patients an estimated high risk for complications of bleeding contributed to this decision. After a median follow-up of 36 months (140 patient-years) recurrent events, complications of bleeding and some basic quality of life measurements regarding the new treatment were registered. No recurrent events, four minor bleedings and no major bleedings were registered. Twenty-six patients preferred an INR of 1.5-2 compared to 2-3. The main reasons for that preference were a lower risk for bleeding (13 patients) and less frequent monitoring of the INR (18 patients). No patient preferred full-dose anticoagulation at INR 2-3. In patients at a high risk for recurrence of VTE an initial period of regular intensity anticoagulation, followed by a low-intensity regimen, may provide effective and safe secondary prophylaxis.