title: Comparison of Warfarin Dosages and International Normalized Ratios Before and After Roux-en-Y Gastric Bypass Surgery.
abstract: OBJECTIVE
  As data are limited for dosing warfarin in patients who have undergone bariatric surgery, our objective was to gather data on warfarin pharmacotherapy to aid in the prescribing practices and dosage adjustment of warfarin after Roux-en-Y gastric bypass (RYGB) surgery.
  
  
  METHODS
  Retrospective medical record review.
  
  
  METHODS
  Anticoagulation clinic.
  
  
  METHODS
  Twelve patients who underwent RYGB surgery between 2009 and 2011.
  
  
  RESULTS
  Data were collected on patient demographics, therapeutic indications for warfarin, weekly warfarin doses, and international normalized ratio (INR) values before and after RYGB surgery. To examine whether the relationship between the warfarin dose and therapeutic effect (i.e., INR) of warfarin changed from before to after surgery, we generated a ratio between each INR measurement and the weekly warfarin dose that immediately preceded it (warfarin dose/INR ratio). Mean weekly warfarin dose after RYGB surgery decreased significantly relative to presurgery dose (estimated marginal mean ± SE presurgery dose 37.08 ± 3.31 mg vs postsurgery dose 28.08 ± 3.27 mg; [F(205.63) = 13.23, p<0.001]), whereas INRs increased significantly after surgery from presurgery levels (estimated marginal mean ± SE presurgery INR 2.36 ± 0.15 vs postsurgery INR 2.94 ± 0.14; [F(213.76) = 6.55, p<0.05]). The ratio of warfarin dose/INR from presurgery (estimated marginal mean ± SE 17.64 ± 1.67) to postsurgery (estimated marginal mean ± SE 10.94 ± 1.64) was also significantly reduced [F(206.47) = 20.61, p<0.001], suggesting that a lower warfarin dose was required to produce the desired INR after surgery compared with before surgery.
  
  
  CONCLUSIONS
  Warfarin dosages tended to decrease after RYGB surgery, in agreement with previously published literature. These findings suggest the need for increased INR monitoring and patient education for patients taking warfarin after RYGB surgery.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, College of Health Professions, North Dakota State University, Fargo, North Dakota.|Neuropsychiatric Research Institute, Fargo, North Dakota.
authors.forename: Kristine J
authors.initials: KJ
authors.lastname: Steffen
authors.affiliation: Neuropsychiatric Research Institute, Fargo, North Dakota.
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Wonderlich
authors.affiliation: Neuropsychiatric Research Institute, Fargo, North Dakota.
authors.forename: Ann L
authors.initials: AL
authors.lastname: Erickson
authors.affiliation: Sanford Health Anticoagulation Clinic, Fargo, North Dakota.
authors.forename: Heather
authors.initials: H
authors.lastname: Strawsell
authors.affiliation: Neuropsychiatric Research Institute, Fargo, North Dakota.|Department of Neuroscience, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota.
authors.forename: James E
authors.initials: JE
authors.lastname: Mitchell
authors.affiliation: Neuropsychiatric Research Institute, Fargo, North Dakota.|Department of Neuroscience, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota.
authors.forename: Ross D
authors.initials: RD
authors.lastname: Crosby
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D015390:Gastric Bypass / Q000379:methods*; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014859:Warfarin / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D000925:Anticoagulants; D014859:Warfarin
keywords: INR; Roux-en-Y gastric bypass; anticoagulant; bariatric surgery; international normalized ratio; pharmacokinetic; warfarin