Comparison of Warfarin Dosages and International Normalized Ratios Before and After Roux-en-Y Gastric Bypass Surgery

Study 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. Design Retrospective medical record review. Setting Anticoagulation clinic. Patients Twelve patients who underwent RYGB surgery between 2009 and 2011. Measurements and Main 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