Fixed Minidose Versus-adjusted Low-dose Warfarin After Total Joint Arthroplasty: a Randomized Prospective Study

Widespread use of adjusted low-dose warfarin has been limited by the inconvenience of outpatient laboratory monitoring and the perceived risk of bleeding complications. We sought to determine if the dose of warfarin could be lowered safely even further, eliminating the need for laboratory monitoring and lowering the complication rate. Two hundred forty-five Patients undergoing primary total joint arthroplasty (n = 245) were randomized prospectively to adjusted low-dose warfarin (international normalized ratio [INR], 1.4-1.8) or fixed minidose warfarin (2 mg daily, regardless of INR) before hospital discharge. Prophylaxis continued for 6 weeks, with twice-weekly laboratory monitoring. Patients were followed for bleeding, thromboembolic events, and minor reported complications of warfarin therapy. With the numbers available, the rates of thromboembolic and bleeding events were not significantly different using equivalence analysis. Of patients in the fixed group, 8% had INRs >3.1, necessitating a decrease in dosage to 1 mg. Although such a fixed-dose protocol may simplify outpatient prophylaxis, intermittent monitoring still would be required because a subset of patients achieve a moderate level of anticoagulation and would be at risk for bleeding complications.