title: Feasibility of Extended-interval Follow-up for Patients Receiving Warfarin.
abstract: OBJECTIVE
  The 2012 American College of Chest Physician Evidence-Based Management of Anticoagulant Therapy guidelines suggest an international normalized ratio (INR) testing interval of up to 12 weeks, rather than every 4 weeks, for patients with consistently stable INRs while taking vitamin K antagonists. We aimed to examine the feasibility of extended-interval follow-up in a real-world setting.
  
  
  METHODS
  Patients receiving stable warfarin therapy for ≥ 12 weeks at baseline began extended-interval follow-up with visits occurring at 6 weeks, 14 weeks, and every 12 weeks thereafter to a maximum of 68 weeks or until they were no longer suitable for extended-interval follow-up. A single INR excursion >0.3 from goal was permitted if a reversible precipitating factor was identified and the INR was expected to return to goal without dose adjustment. The primary outcome was the proportion of patients completing all study follow-up visits.
  
  
  RESULTS
  Of 48 patients enrolled, 47 had evaluable data. The most common indication for anticoagulation was atrial fibrillation/flutter (53.2%). At baseline, mean prior warfarin treatment duration was 6.7 ± 6 years and median number of weeks on a stable regimen was 24 weeks (IQR, 19-37.5). Eleven patients (23%) completed all study follow-up visits, whereas 17 (36%) did not maintain a stable INR past the 14-week follow-up.
  
  
  CONCLUSIONS
  A large proportion of patients with previously stable (≥ 3 months) INRs were not able to maintain stable INRs during extended-interval follow-up. More research is needed to identify patient characteristics predictive of success with extended-interval follow-up prior to broad implementation.
authors: Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.|Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: Nicholas W
authors: NW
authors: Carris
authors: Department of Pharmacy Practice, Belmont University College of Pharmacy, Nashville, TN, USA.
authors: Alisa
authors: A
authors: Spinelli
authors: Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: Danielle
authors: D
authors: Pierini
authors: Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: James R
authors: JR
authors: Taylor
authors: Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.|Division of Internal Medicine, Department of Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.
authors: Katherine Vogel
authors: KV
authors: Anderson
authors: Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.|Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: Karen
authors: K
authors: Sando
authors: Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: Jason
authors: J
authors: Powell
authors: Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.|Division of Internal Medicine, Department of Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.
authors: Eric I
authors: EI
authors: Rosenberg
authors: Division of Hematology/Oncology, Department of Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.
authors: Marc S
authors: MS
authors: Zumberg
authors: Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.|Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: Steven M
authors: SM
authors: Smith
authors: Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.|Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: John G
authors: JG
authors: Gums
authors: Department of Community Health and Family Medicine, College of Medicine, University of Florida, Gainesville, FL, USA.|Department of Pharmacotherapy and Translational Research, College of Pharmacy, University of Florida, Gainesville, FL, USA.
authors: Eric
authors: E
authors: Dietrich
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage / Q000627:therapeutic use*; D001281:Atrial Fibrillation / Q000188:drug therapy*; D016903:Drug Monitoring / Q000379:methods*; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D011446:Prospective Studies; D012307:Risk Factors; D013997:Time Factors; D014859:Warfarin / Q000008:administration & dosage / Q000627:therapeutic use*; D055815:Young Adult
chemical_list: D000925:Anticoagulants; D014859:Warfarin
keywords: Anticoagulation; interval; monitoring; warfarin