Evaluation of the safety and efficacy of warfarin in Taiwanese patients

Objective: The safety and efficacy of warfarin therapeutic range in Asians remain to be ascertained. Physicians in Taiwan consider Asians are more likely to have bleeding complications rather than thromboembolic events from warfarin. The aim of this study was to determine if the proper INR range for patients in Taiwan is different. Methods: A retrospective study was conducted with 161 patients on warfarin therapy for more than 24 consecutive months during March 1, 2006 to Sepember 30, 2008. Total follow-up time was 3,504 patient-months. The incidence rates of thromboembolic and bleeding events for INR categories were calculated. Results: The overall incidence rates of INR ranges of < 1.5, 1.5 - 1.9, 2.0 - 2.4, 2.5 - 2.9, 3.0 - 3.4, and ≥ 3.5 were 8.1, 5.6, 2.0, 7.6, 33.3, and 121.2 per 1,000 patientmonths, respectively. The overall incidence rate at INR of > 3 is higher than that at INR of < 2 or 2 - 3 (p < 0.001), with the lowest incidence rate at INR between 2.0 and 2.4. When INR was maintained at a level < 2, patients taking warfarin for secondary prevention had a significantly higher event rate compared to the primary prevention group (p < 0.05). Age greater than 73 years was a risk factor for thromboembolic events before and after covariate adjustment. Conclusion: An INR range of 2 - 2.4 appeared to be associated with lower complications and better clinical outcomes in Taiwanese patients treated with warfarin. Lowering the intensity of anticoagulant therapy further does not decrease the number of events.