OBJECTIVES: To model the costs of thromboprophylaxis following total hip arthroplasty (THA) with either low-intensity warfarin, enoxaparin, or fondaparinux. METHODS: This was a cost-minimization analysis of anticoagulants expected to have equivalent tolerability and effectiveness.  Data were obtained from an HMO’s joint replacement registry.  Patients were included if they had THA between August 2005 and March 2009, continuous enrollment in the 180 days prior to and 90 days following THA, utilized low-intensity warfarin thromboprophylaxis, and had not been chronically anticoagulated previously.  Patients received warfarin therapy supervised through a pharmacist-run anticoagulation service that included mobile phlebotomy for INR monitoring.  Iterative modeling from the HMO’s perspective utilized registry data to calculate the costs of thromboprophylaxis with anticoagulants at 2010 AWP minus 35%, monitoring at $50 per phlebotomy, $15 per INR, and 0.1 hour pharmacist time (at $75/hr) per INR.  Patient training for any anticoagulant use was included at 0.25 hr pharmacist time. Duration of therapy was modeled to a mean of 35 days for injectible (enoxaparin and fondaparinux) thromboprophylaxis for which monitoring services would not be required.  Sensitivity analyses included reducing AWPs by 25% prior to discounting and increasing phlebotomy and INRs to $75 and $25, respectively. RESULTS:   835 THAs for 800 patients were included.  The mean age and duration warfarin therapy were 66 years and 40 days, respectively, and 62% were females. The base-case thromboprophylaxis cost was $556 (95% CI=$545-$567), $701 (95% CI=$693-$709), and $2677 (95% CI=$2646-$2708) for warfarin, enoxaparin, and fondaparinux, respectively. 25% AWP reduction resulted in thromboprophylaxis costs of $553 (95% CI=$542-$564), $564 (95% CI=$558-$571), and $2145 (95% CI=$2120-$2171) for warfarin, enoxaparin, and fondaparinux, respectively.   Increasing monitoring costs resulted in thromboprophylaxis cost of $756 (95% CI=$740-$771) for warfarin. CONCLUSIONS: Warfarin thromboprophylaxis had the lowest cost but is sensitive to monitoring costs whereas injectible thromboprophylaxis is sensitive to drug acquisition costs.