Assessment of Dosing and Patient Factors on the Efficacy of Warfarin Following Total Joint Replacement

Ryan Murphy 1, Annamarie Stehli 2, Hiep Nguyen 3, Szu-Yun Leu 2, 5, Danh V Nguyen 2, 4, Ran Schwarzkopf *, 1
1 Department of Orthopaedic Surgery, University of California, Irvine School of Medicine, USA
2 Institute for Clinical and Translational Science, University of California, Irvine, CA 92687, USA
3 Inpatient Pharmacy, University of California, Irvine Medical Center, USA
4 Department of Medicine, University of California Irvine, Orange, CA 92868, USA
5 Department of Pediatrics, University of California, Irvine School of Medicine, USA

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© Murphy et al.; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the 101 The City Drive South, Pavilion III, Building 29, Orange, CA 92868, USA; Tel: - 714-456-5759; Fax: 714-456-7547; E-mail:


The purpose of this study was to determine the percentage of patients discharged with a subtherapeutic INR <1.8 using our institutions inpatient warfarin dosing nomogram following total joint arthroplasty (TJA). We examined predisposing risk factors for a subtherapeutic discharge (INR <1.8), including increased body weight, age, gender, end stage renal disease (ESRD), smoking, and peri-operative transfusion.

Chart review identified 249 patients for study inclusion. Logistic regression (LR) was used to identify associated risk factors for a subtherapeutic INR (<1.8) on day of discharge.

The majority of patients (58.6%, 146 of 249) following TJA surgery were found to have a subtherapeutic INR level (INR<1.8) at discharge (mean length of stay 2.6 days). Multivariate LR analysis found that weight greater than 180 lbs. (OR 2.08, CI 1.09, 3.98, P=0.027) was found to increase the odds of a subtherapeutic INR on day of discharge. Our results were not significant for weight 20% beyond ideal body weight, age (>65y), gender, peri-operative transfusion, smoking, ESRD or autoimmune disease.

A patient’s body weight influences response to warfarin following TJA. An inpatient warfarin dosing nomogram that takes into account a patient’s weight should be used to reduce the risk of subtherapeutic INR levels in obese TJA patients.

Keywords: Coumadin, venous thromboembolism (VTE), warfarin international normalized ratio (INR).