title: Thromboembolic and bleeding outcomes of extended duration low-intensity warfarin following elective total knee arthroplasty.
abstract: BACKGROUND
  The purpose of this study was to describe the incidence of symptomatic venous thromboembolism (VTE), clinically-relevant bleeding, and death among a real-world population receiving warfarin prophylaxis targeting an international normalized ratio (INR) of 1.5 to 2.5 for four weeks following total knee arthroplasty (TKA).
  
  
  METHODS
  This retrospective, observational study included patients receiving warfarin following a TKA between August 1, 2005 and July 31, 2009 identified in the Kaiser Permanente Total Joint Replacement Registry. Patients<18 years, receiving warfarin for another indication, or without continuous KPCO membership during the study period were excluded.
  
  
  RESULTS
  There were 1487 patients with TKA included in the analysis. Mean patient age was 67.7 years and 61.7% were female. The median percent of time in therapeutic INR range during follow-up was 55% (interquartile range=35%-75%). Nineteen cases of symptomatic VTE [1.3%; 95% confidence interval (CI) 0.8%-2.0%] including ten pulmonary emboli (PE) (0.7%) were identified within 90 days of surgery. Clinically-relevant bleeding occurred in 1.7% (95% CI 1.1%-2.5%) of patients during warfarin prophylaxis and there were no deaths within 90 days of surgery.
  
  
  CONCLUSIONS
  The rates of symptomatic VTE and clinically-relevant bleeding following TKA in patients receiving warfarin prophylaxis with a target INR of 1.5 to 2.5 were low. Additional studies should include low-intensity warfarin to identify the regimen that optimally balances risks of bleeding and symptomatic VTE after major orthopedic surgery.
authors.affiliation: At the time of research, Ambulatory Care Specialty Resident, Pharmacy Department, Kaiser Permanente Colorado, Aurora, CO, USA; Clinical Pharmacy Anticoagulation and Anemia Services, Kaiser Permanente Colorado, Aurora, CO, USA.
authors.forename: Stephanie E
authors.initials: SE
authors.lastname: Cho
authors.affiliation: Clinical Pharmacy Research Team, Kaiser Permanente Colorado, 16601 E. Centretech ParkwayAurora, CO 80011, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Delate
authors.affiliation: At the time of research, Clinical Pharmacy Research Team, Kaiser Permanente Colorado, Aurora, CO, USA.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Witt
authors.affiliation: Clinical Pharmacy Anticoagulation and Anemia Services, Kaiser Permanente Colorado, Aurora, CO, USA. Electronic address: nathan.clark@kp.org.
authors.forename: Nathan P
authors.initials: NP
authors.lastname: Clark
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000627:therapeutic use*; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects* / Q000379:methods; D015331:Cohort Studies; D005260:Female; D006470:Hemorrhage / Q000188:drug therapy*; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D013923:Thromboembolism / Q000188:drug therapy*; D016896:Treatment Outcome; D014859:Warfarin / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D014859:Warfarin
keywords: Arthroplasty; Deep vein thrombosis; Pulmonary embolism; Thromboprophylaxis; Warfarin