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ANTICOAGULATION

Low-Dose Warfarin for Prevention of Symptomatic Thromboembolism After Orthopedic Surgery

at time of study, Pharmacy Student, College of Pharmacy, Butler University, Indianapolis, IN; now, Clinical Pharmacist, Lutheran Hospital of The Lutheran Health Network, Fort Wayne, IN

Ronald J Jones, PharmD

Associate Professor of Clinical Pharmacy, College of Pharmacy, Ohio Northern University, Ada, OH; Adjunct Assistant Professor, College of Pharmacy, Butler University; Clinical Educator/Practitioner, Lutheran Hospital of The Lutheran Health Network

Reprints: Dr. Jones, Pharmacy Department, Lutheran Hospital, Fort Wayne, IN 46804-4160, fax 260/435-7609, r-jones{at}onu.edu

BACKGROUND: Warfarin dosing with a target international normalized ratio (INR) range of 1.5–2.5 has not been reported as adequate for venous thromboembolism (VTE) prophylaxis after total knee (TKR) and total hip replacement (THR) surgery.

OBJECTIVE: To evaluate the rate of symptomatic VTE after TKR and THR surgery using a low-dose (INR 1.5–2.5) warfarin protocol started the evening before surgery compared with a literature cohort treated with enoxaparin.

METHODS: TKR/THR patients treated with a 21-day low-dose warfarin protocol were followed via a consecutive observational design. Main outcome measures were symptomatic VTE and pulmonary embolism (PE), with major bleeds and death as secondary outcomes. Low-dose warfarin was compared with a literature cohort of patients treated with enoxaparin who received enoxaparin for a similar length of time and was evaluated for the same outcomes. Cohort event rates were derived as a weighted average using the DerSimonian model.

RESULTS: VTE, PE, bleeds, and deaths in the low-dose warfarin group were 8 (1.04%), 4 (0.52%), 8 (1.04%), and 4 (0.52%), respectively. The cohort weighted average values were 35 (1.33%), 19 (0.72%), 65 (2.46%), and 18 (0.67%), respectively. Odds ratios for low-dose warfarin for VTE, PE, and VTE plus PE were 0.778 (95% CI 0.36 to 1.68), 0.717 (0.24 to 2.11), and 0.754 (0.41 to 1.42), respectively, all nonsignificant. Odds ratios for bleeds and death were 0.420 (0.20 to 0.87; p = 0.02) and 0.756 (0.26 to 2.24; NS), respectively.

CONCLUSIONS: For this evaluation, low-dose warfarin was comparable to the enoxaparin cohort for development of VTE, PE, and VTE+PE. Incidences of bleeds in the enoxaparin cohort were significantly higher than in patients receiving low-dose warfarin.

Key Words: arthroplasty, enoxaparin, low-molecular-weight heparin, thromboembolism, total hip replacement, total knee replacement, warfarin

Published Online, May 10, 2005. www.theannals.com, DOI 10.1345/aph.1E536

This article has been cited by other articles:

				S. A Spinler and R. J Friedman Comment: low-dose warfarin for prevention of symptomatic thromboembolism after orthopedic surgery Ann. Pharmacother., November 1, 2005; 39(11): 1954 - 1955. [Full Text] [PDF]