Superiority of fixed-dose warfarin for chronic anticoagulation

Long-term anticoagulation for stroke prevention is a labor-intensive endeavor, requiring close monitoring of patients to maintain efficacy and avoid toxicity. Theoretically, fixed daily doses of warfarin may facilitate the establishment and maintenance of anticoagulation, with lesser fluctuations of the international normalized ratio (INR), and favor long-term compliance. This pilot project aimed at assessing the potential advantages of fixed daily dosing for chronic anticoagulation.

We compared the experiences of two separate practices within the same institution. Clinic A exclusively uses fixed daily doses. Clinic B allows the use of variable doses. The anticoagulation records of 96 patients (47 from clinic A and 49 from Clinic B) were reviewed. The incidences of INRs outside target range, occurrence of dose changes or interventions, and magnitude of dose changes were recorded at 1, 3, 6, 9 and 12 months after the institution of anticoagulation. Data were analyzed using Chi square analysis.

The demographic characteristics of both groups were comparable. Of the 576 INRs recorded during a period of 12 months, 316 were outside target range. There were 126 INRs outside target range in group A and 190 in group B (P < .0001). Group B accounted for 103 of the 169 dose changes resulting from an INR outside target range, whereas group A accounted for 66 (P < .05). The number of interventions and magnitude of dose changes were similar in both groups.

Fixed daily dosing offers several advantages over variable dosing in maintaining anticoagulation.