More is Less: Extended Enoxaparin After Surgery for Inflammatory Bowel Disease - A Cost-based Decision-Analysis

Abstract

Inflammatory Bowel Disease (IBD) patients undergoing colorectal surgery are at an increased risk of Venous Thromboembolism (VTE), particularly beyond 10 days post-op. Optimal VTE prophylaxis, however, is not well defined in this population. In cancer patients undergoing abdominopelvic surgery, several randomized trials suggested that extended therapy with enoxaparin was a more effective treatment strategy, while several decision analyses suggested subcutaneous heparin may result in more cost minimization. These previous studies were performed prior to the availability of generic enoxaparin and failed to incorporate rates of patient compliance. Thus we aimed to construct a cost minimization decision analysis which included these important factors in a population known to be at high-risk for VTE. We constructed a cost minimization decision model to evaluate four strategies for management of postoperative VTE risk after surgery for IBD: (1) inpatient subcutaneous heparin (SQH) 5000 units TID × 10 days; (2) inpatient enoxaparin 40 mg daily × 10 days; (3) SQH 5000 units TID × 30 total days (10 inpatient, 20 outpatient days); (4) enoxaparin 40 mg daily × 30 total days (10 inpatient, 20 outpatient days). Our model made the following assumptions: (1) no prior history of VTE; (2) only major bleeding required intervention; (3) 90% of major bleeds were treated medically with transfusion of 2 units PRBC and 10% required reoperation; (4) heparin-induced thrombocytopenia (HIT) occurred within the first 10 days of exposure. Rates of inpatient and outpatient VTE, adherence to outpatient treatment, and strategy specific complications including HIT and major bleeding for each strategy, were obtained from published literature and modeled. Costs (in US dollars), including costs of strategy specific complications, were based on published literature, institutional charges and average wholesale pricing. Sensitivity analyses were performed to account for uncertainty in estimates. In this model, extended duration prophylaxis with enoxaparin was associated with the greatest cost minimization with an estimated cost of $2,585, compared to extended SQH which cost $2,768. Inpatient-only prophylaxis with enoxaparin and SQH cost $2,944 and $3,267, respectively. Our model was sensitive to rates of VTE (Figure 1), rates of HIT, and drug costs (Figure 2). Sensitivity analysis revealed that the extended SQH strategy was associated with the most cost minimization when VTE rates with enoxaparin were >6.5% (vs. 5.7% in the base case) and costs of outpatient enoxaparin were >$712 (vs. $528 in the base case). SQH was also associated with the most cost minimization if patient adherence rates were >85% (vs. 65% in the base case). Our model, in contrast to previously published cancer surgery literature, suggests that in IBD patients extended duration prophylaxis with enoxaparin for a total of 30 days post-operatively would result in the greatest costminimization. This may be in part due to the availability of generic enoxaparin, reduced risk of HIT, and increased adherence with outpatient enoxaparin resulting in greater VTE prevention relative to SQH.