title: Levothyroxine absorption in morbidly obese patients before and after Roux-En-Y gastric bypass (RYGB) surgery.
abstract: BACKGROUND
  Roux-en-Y gastric bypass (RYGB) modifies the anatomical structure of the upper intestine tract, reduces gastric acid secretion, and may impair LT4 absorption. The aim of this study was to evaluate the LT4 absorption in morbidly obese patients before and after RYGB.
  
  
  METHODS
  Thirty morbidly obese patients were divided in two groups: The NS group included 15 patients before RYGB surgery (BMI = 43.1 ± 4 kg/m(2)), and the S group included 15 patients after surgery (BMI = 37.3 ± 4 kg/m(2)). Two baseline samples were collected, and 600 μg of oral LT4 tablets were administered. Blood samples were collected at 30, 60, 120, 180, 240, 300, and 1440 min. Serum-free T4 (FT4), total T4 (TT4), and TSH were measured at each time point. The increase in TT4, FT4, and TSH (ΔTT4, ΔFT4, and ΔTSH) was calculated, subtracting from the baseline mean value.
  
  
  RESULTS
  The pharmacokinetics parameters regarding LT4 absorption, maximum ΔTT4, and area under the curve(AUC) of both ΔTT4 and ΔFT4 were significantly higher in the S group compared with the NS group (p < 0.05). It was observed, however, that there was a significant delay in the absorption of LT4 in the S group. Basal serum TSH and leptin levels were higher in the NS group (p = 0.016 and 0.026, respectively), whereas basal serum TT4, FT4, ΔTSH, and the AUC of ΔTSH were similar between groups.
  
  
  CONCLUSIONS
  In this study, we have demonstrated that Roux-en-Y bypass surgery does not diminish LT4 absorption. A small but significant delayed absorption of LT4, however, was observed in patients after surgery.
authors.affiliation: Department of Biological Sciences, Federal University of São Paulo, Rua Prof. Artur Riedel 275, Eldorado, Diadema, São Paulo 09972-270, Brazil.
authors.forename: Ileana Gabriela Sanchez
authors.initials: IG
authors.lastname: Rubio
authors.forename: Ana Luiza
authors.initials: AL
authors.lastname: Galrão
authors.forename: Marco Aurelio
authors.initials: MA
authors.lastname: Santo
authors.forename: Antonio Carlos
authors.initials: AC
authors.lastname: Zanini
authors.forename: Geraldo
authors.initials: G
authors.lastname: Medeiros-Neto
mesh_terms: D000293:Adolescent; D000328:Adult; D015331:Cohort Studies; D004305:Dose-Response Relationship, Drug; D005260:Female; D005500:Follow-Up Studies; D015390:Gastric Bypass; D006801:Humans; D007037:Hypothyroidism / Q000150:complications / Q000188:drug therapy* / Q000378:metabolism; D007408:Intestinal Absorption / Q000187:drug effects*; D008297:Male; D008875:Middle Aged; D009767:Obesity, Morbid / Q000188:drug therapy / Q000209:etiology / Q000378:metabolism* / Q000601:surgery*; D011182:Postoperative Care; D011300:Preoperative Care; D011446:Prospective Studies; D013974:Thyroxine / Q000378:metabolism / Q000493:pharmacokinetics*; D015431:Weight Loss; D055815:Young Adult
chemical_list: D013974:Thyroxine