Adjustments to warfarin dosing after gastric bypass and sleeve gastrectomy

Surg Obes Relat Dis. 2018 May;14(5):700-706. doi: 10.1016/j.soard.2017.12.021. Epub 2018 Jan 2.


Background: Warfarin dosing after bariatric surgery may be influenced by alterations in gastrointestinal pH, transit time, absorptive surface area, gut microbiota, food intake, and adipose tissue.

Objectives: The aim of this study was to describe trends in warfarin dosing after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG).

Setting: Single academic center.

Methods: All patients chronically on warfarin anticoagulation before RYGB or SG were retrospectively identified. Indications for anticoagulation, history of bleeding or thrombotic events, perioperative complications, and warfarin dosing were collected.

Results: Fifty-three patients (RYGB n = 31, SG n = 22) on chronic warfarin therapy were identified (56.6% female, mean 54.4 ± 11.7 yr of age). Of this cohort, 34.0% had prior venous thromboembolic events, 43.4% had atrial fibrillation, and 5.7% had mechanical cardiac valves. Preoperatively, the average daily dose of warfarin was similar in the RYGB group (8.3 ± 4.1 mg) and SG group (6.9 ± 2.8 mg). One month after surgery, mean daily dose of warfarin was reduced 24.1% in the RYGB group (P<.001) and 23.2% in the SG group (P = .002). At 12 months postoperatively, the required daily warfarin dose compared with baseline remained statistically different (RYGB: 6.8 ± 3.8 mg; SG: 6.1 ± 2.0 mg).

Conclusions: The warfarin dose is expected to be decreased by approximately 25% from preoperative levels after both RYGB and SG. Lower dose requirement within the first month after bariatric surgery is followed by a trend toward increased warfarin dose requirements, but remain less than baseline. Because dose requirements change constantly over time, frequent postoperative monitoring of the international normalized ratio is recommended.

Keywords: Anticoagulation; Bleeding; Gastric bypass; INR; Sleeve gastrectomy; Thrombosis; Warfarin.

MeSH terms

  • Anticoagulants / administration & dosage*
  • Atrial Fibrillation / complications
  • Bariatric Surgery / methods*
  • Drug Administration Schedule
  • Female
  • Gastrectomy / methods
  • Gastric Bypass / methods
  • Heart Valve Prosthesis
  • Hemorrhage / complications
  • Humans
  • International Normalized Ratio
  • Laparoscopy / methods*
  • Male
  • Middle Aged
  • Obesity, Morbid / complications
  • Obesity, Morbid / surgery
  • Postoperative Care
  • Preoperative Care / methods
  • Retrospective Studies
  • Venous Thromboembolism / complications
  • Warfarin / administration & dosage*


  • Anticoagulants
  • Warfarin