title: Improved levothyroxine pharmacokinetics after bariatric surgery.
abstract: BACKGROUND
  The absorption of levothyroxine (LT4) is affected by many factors. Bariatric surgery is recommended in severely obese patients. The aim of this study was to determine the consequences of bariatric surgery on LT4 pharmacokinetic parameters, and to identify the regions of the gastrointestinal tract where LT4 is absorbed in patients with severe obesity before and after surgery.
  
  
  METHODS
  We studied 32 severely obese nonhypothyroid patients who underwent sleeve gastrectomy (SG; n=10), Roux-en-Y gastric bypass (RYGBP; n=7), or biliopancreatic diversion with long limbs (BPD-LL; n=15). Before surgery, from 8:00 a.m., blood samples were collected before and every 30 minutes after the oral administration of a solution of 600 μg of LT4. The same procedure was repeated 35 days after surgery. We estimated the pharmacokinetic parameters of LT4 before and after surgery, including the area under the curve (AUC), the peak thyroxine concentration (Cmax), and the time to peak thyroxine concentration (Tmax).
  
  
  RESULTS
  Following surgery, in the SG group, the mean AUC was higher than it was before surgery (18.97±6.01 vs. 25.048±6.47 [μg/dL]·h; p<0.01), whereas the values of Cmax and Tmax were similar to those before surgery. In the RYGBP group, mean AUC, Cmax, and Tmax were similar before and after surgery. In the BPD-LL group, mean AUC and Cmax were higher after surgery than before (14.18±5.64 vs. 25.51±9.1 [μg/dL]·h, p<0.001; 5.62±1.34 vs. 8.16±2.57 μg/dL, p<0.001, respectively), whereas Tmax was similar.
  
  
  CONCLUSIONS
  The pharmacokinetic parameters of LT4 absorption are improved following SG and BPD-LL types of bariatric procedures. We conclude that the stomach, the duodenum, and the upper part of the jejunum are not sites for LT4 absorption, because in the above-mentioned bariatric procedures these are bypassed or removed.
authors.affiliation: Division of Endocrinology, Department of Internal Medicine, University Hospital of Patras, Patras, Greece.
authors.forename: Margarita
authors.initials: M
authors.lastname: Gkotsina
authors.forename: Marina
authors.initials: M
authors.lastname: Michalaki
authors.forename: Irene
authors.initials: I
authors.lastname: Mamali
authors.forename: Georgios
authors.initials: G
authors.lastname: Markantes
authors.forename: George C
authors.initials: GC
authors.lastname: Sakellaropoulos
authors.forename: Fotios
authors.initials: F
authors.lastname: Kalfarentzos
authors.forename: Apostolos G
authors.initials: AG
authors.lastname: Vagenakis
authors.forename: Kostas B
authors.initials: KB
authors.lastname: Markou
mesh_terms: D000293:Adolescent; D000328:Adult; D050110:Bariatric Surgery; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000378:metabolism* / Q000601:surgery; D013963:Thyroid Hormones / Q000097:blood; D013974:Thyroxine / Q000493:pharmacokinetics*; D016896:Treatment Outcome
chemical_list: D013963:Thyroid Hormones; D013974:Thyroxine