A pharmacoeconomic assessment of enoxaparin and warfarin as prophylaxis for deep vein thrombosis in patients undergoing knee replacement surgery

Abstract

This paper examines the relative cost-effectiveness of enoxaparin and warfarin as prophylactic therapy for the prevention of deep vein thrombosis (DVT) in patients undergoing knee replacement surgery in a managed care setting. Although enoxaparin is more expensive than warfarin, it is also more effective in the prevention of DVT after knee replacement surgery. To date there has been no comprehensive assessment of the cost-effectiveness of the alternative agents used for this purpose. This evaluation is undertaken using a decision model that contrasts enoxaparin and warfarin regimens. The model takes explicit account of the incidence of proximal DVT, distal DVT, pulmonary embolism (PE), and major bleeds. The probabilities of clinical events are taken from data from a published randomized, controlled, clinical trial. Key assumptions are that PEs derive only from asymptomatic proximal DVTs and that a false-positive diagnosis of DVT is made in 10% of cases. Unit resource cost data are taken from pharmacoeconomic studies of DVT prophylaxis in hip replacement surgery. The analysis focuses on the actual or expected cost of prophylactic treatment using enoxaparin as opposed to warfarin and, as appropriate measures of cost-effectiveness, the cost per DVT event avoided and the cost per incidence of PE avoided. The expected cost of warfarin prophylaxis is $105 less per patient than that of enoxaparin. In terms of expected cost per DVT event avoided, enoxaparin prophylaxis is $2525 less than for warfarin; in terms of expected cost per PE avoided, it is $87,201 less. Enoxaparin is more cost-effective than warfarin in terms of both DVT events and PEs avoided in patients who have undergone knee replacement surgery.