Subcutaneous low-molecular-weight heparin vs warfarin for prophylaxis of deep vein thrombosis after hip or knee implantation - An economic perspective

Background: Postoperative venous thrombosis and pulmonary embolism present a major clinical threat to patients undergoing total hip or knee arthroplasty. We performed an economic evaluation of warfarin sodium and subcutaneous low-molecular-weight heparin sodium prophylaxis comparing cost and effectiveness. Methods: A consecutive series of 1436 patients who underwent hip or knee arthroplasty comparing these 2 regimens in a randomized trial with objective documentation of outcomes provided the opportunity to perform economic evaluations for Canada and the United States. Results: Deep vein thrombosis was documented in 231 (37.4%) of 617 patients given warfarin and in 185 (31.4%) of 590 patients given low-molecular-weight heparin (P=.03). In Canada, warfarin and low-molecular-weight heparin (tinzaparin sodium) incurred costs per 100 patients of $11598 and $9197, respectively, providing a cost savings of $2401 for the low-molecular-weight heparin group. The drug cost of low-molecular-weight heparin (tinzaparin) was $6 per day and for warfarin was $0.32 per day. Sensitivity analysis showed that low-molecular-weight heparin is more costly if drug costs are increased by 1.5-fold (ie. the cost of tinzaparin is increased from $6 per day to $8.82 per day or more). In the United States, the analysis was also not definitive; low-molecular-weight heparin was more costly than warfarin at drug costs of $15 and $2.01 per day, respectively. Conclusions: Our findings indicate that the decision to use low-molecular-weight heparin or warfarin prophylaxis in patients undergoing major joint replacement surgery is a finely tuned trade-off. Prophylaxis with low-molecular-weight heparin is equally or more effective than the more complex prophylaxis with warfarin. Major bleeding is uncommon but less frequent with warfarin use. The most significant parameters that influence the comparative cost-effectiveness are the cost of the drug, the cost of international normalized ratio monitoring, and the costs associated with major bleeding. The analysis also demonstrates that the results are health care system dependent (Canada vs US). In Canada, low-molecular-weight heparin (tinzaparin) is less costly because it avoids the need for international normalized ratio monitoring. In the United States, the drug cost for low-molecular-weight heparin will likely be the principal determinant of relative cost-effectiveness.