Low-Molecular-Weight Heparin Therapy for Patients Undergoing Total Knee Replacement Surgery: Cost and Outcomes

Abstract

Objective: In March 1997, a community hospital system changed the low-molecular-weight heparin (LMWH) product on formulary from enoxaparin to dalteparin through a therapeutic interchange for all uses except patients undergoing total knee replacement (TKR) surgery. In October 1997, therapeutic interchange of LMWHs (enoxaparin to dalteparin) was instituted for patients undergoing TKR surgery. The cost equivalence of these therapies in TKR surgery was evaluated. Methods: A cohort of patients admitted to three health-system facilities who underwent primary TKR surgery between July 1, 1996 and December 31, 1998 was assembled retrospectively. Costs and outcomes associated with a formulary interchange for LMWH products (from enoxaparin to dalteparin) initiated in October 1997 for TKR surgery were analyzed using data abstracted hospital records and decision support systems. To evaluate equivalence between the drugs, the difference in median inpatient health care costs (with 95% confidence intervals [CIs]) was calculated. Equivalence of outcomes (eg, adverse events) in terms of risk ratios was also evaluated. Results: Inpatient costs were essentially equivalent for patients treated with enoxaparin (n = 88) and dalteparin (n = 101), with a slightly higher median cost among enoxaparin-treated patients ($172 [95% CI, -$17 to + $395]). CIs for the crude and regression-adjusted findings included the possibility of no cost difference (ie, $0). The median time to hospital discharge was identical, at 6 days. Outcomes were otherwise similar between the two groups. Conclusions: Our therapeutic interchange program was successful. Inpatient costs were equivalent when patients were treated with either enoxaparin or dalteparin for TKR surgery.