title: Are levothyroxine requirements lower in thyroidectomized diabetic patients on metformin treatment?
abstract: BACKGROUND
  Recent studies have suggested that metformin (MF) may lower thyrotropin concentration. This suggests a possible need for a dose reduction of levothyroxine in hypothyroid patients taking MF. However, contradictory results from heterogeneous study populations indicate that the underlying causes have not been completely elucidated. Patients with postoperative hypothyroidism-a condition not influenced by endogenous thyroid hormone production-have not been evaluated in order to evaluate the impact of MF.
  
  
  OBJECTIVE
  To determine the impact of MF in total thyroidectomized patients receiving levothyroxine replacement.
  
  
  METHODS
  One hundred ninety-two patients underwent total thyroidectomy during three years and were receiving levothyroxine substitution. Patients were divided into two groups depending on MF use: the non-MF group included 159 patients, of whom 134 were women [mean (SD) age, 52 (15.7) years; mean (SD) body weight, 70.2 (13.5) kg; 56 with differentiated thyroid cancer]; the MF group comprised 33 patients, of whom 24 were women [mean (SD) age, 63 (9.8) years; mean (SD) body weight, 79.3 (13.9) kg; 9 with differentiated thyroid cancer]. Levothyroxine requirements were compared between the groups, and the differentiated thyroid cancer cases were also analyzed separately.
  
  
  RESULTS
  Thyrotropin levels did not differ significantly between the MF and the non-MF groups. No differences in total levothyroxine dosage were found: 114 (100-150) [median (Q1-Q3)] μg in the non-MF group versus 125 (100-142) μg in the MF group (p=0.9). When calculating the weight-adjusted levothyroxine dose, significant differences were evident: 1.66 (1.38-2.08) μg/kg in the non-MF group versus 1.53 (1.26-1.70) μg/kg in the MF group (p=0.010). However, in a multivariate regression model with thyrotropin levels, age, body mass index, sex, and type of thyroid disease, MF treatment lost its significance.
  
  
  CONCLUSIONS
  Thyroidectomized patients receiving MF treatment need a lower thyroxine dose than patients who do not receive the drug, possibly due to different characteristics (greater weight, age) of the patients with diabetes mellitus type 2.
authors.affiliation: Department of Endocrinology, Vall d'Hebron University Hospital, Autonomous University of Barcelona , Barcelona, Spain .
authors.forename: Anna
authors.initials: A
authors.lastname: Casteràs
authors.forename: Carles
authors.initials: C
authors.lastname: Zafon
authors.forename: Andreea
authors.initials: A
authors.lastname: Ciudin
authors.forename: Jordi
authors.initials: J
authors.lastname: Mesa
mesh_terms: D000328:Adult; D000368:Aged; D003924:Diabetes Mellitus, Type 2 / Q000150:complications / Q000188:drug therapy*; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D007037:Hypothyroidism / Q000150:complications / Q000188:drug therapy*; D008297:Male; D008687:Metformin / Q000627:therapeutic use*; D008875:Middle Aged; D013965:Thyroidectomy; D013974:Thyroxine / Q000008:administration & dosage / Q000627:therapeutic use*; D016896:Treatment Outcome
chemical_list: D008687:Metformin; D013974:Thyroxine