title: Assessment of Dosing and Patient Factors on the Efficacy of Warfarin Following Total Joint Replacement.
abstract: 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.
authors.affiliation: Department of Orthopaedic Surgery, University of California, Irvine School of Medicine, USA.
authors.forename: Ryan
authors.initials: R
authors.lastname: Murphy
authors.affiliation: Institute for Clinical and Translational Science, University of California, Irvine, CA 92687, USA.
authors.forename: Annamarie
authors.initials: A
authors.lastname: Stehli
authors.affiliation: Inpatient Pharmacy, University of California, Irvine Medical Center, USA.
authors.forename: Hiep
authors.initials: H
authors.lastname: Nguyen
authors.affiliation: Institute for Clinical and Translational Science, University of California, Irvine, CA 92687, USA ; Department of Pediatrics, University of California, Irvine School of Medicine, USA.
authors.forename: Szu-Yun
authors.initials: SY
authors.lastname: Leu
authors.affiliation: Institute for Clinical and Translational Science, University of California, Irvine, CA 92687, USA ; Department of Medicine, University of California Irvine, Orange, CA 92868, USA.
authors.forename: Danh V
authors.initials: DV
authors.lastname: Nguyen
authors.affiliation: Department of Orthopaedic Surgery, University of California, Irvine School of Medicine, USA.
authors.forename: Ran
authors.initials: R
authors.lastname: Schwarzkopf
keywords: Coumadin; venous thromboembolism (VTE); warfarin international normalized ratio (INR)