title: Levothyroxine replacement in primary congenital hypothyroidism: the higher the initial dose the higher the rate of overtreatment.
abstract: BACKGROUND
  Congenital hypothyroidism (CH) is the most frequent endocrine disorder during the neonatal period, and a delay in diagnosis and treatment leads to irreversible complications. A high L-thyroxine (LT4) dose is recommended for treatment, while the optimal starting dose is still a matter of debate. The objective of this study was to determine the effects of various starting doses of LT4 on serum thyroid stimulating hormone (TSH) and thyroxine (fT4) at the end of the first month of treatment.
  
  
  METHODS
  A total of 71 patients (37 males, 52.1%) with CH were included in the study. The patients were designated into three sets of subgroups according to the following categorical variables: (i) initial LT4 doses: 6-9.9 μg/kg/day, 10-11.9 μg/kg/day and 12-17 μg/kg/day; (ii) initial TSH levels: 6-9.99 μIU/mL, 10-75 μIU/mL and >75 μIU/mL; and (iii) etiology: dyshormonogenesis and dysgenesis. A fT4 level >2.3 ng/dL±a TSH level <0.5 μIU/mL were considered as overtreatment.
  
  
  RESULTS
  The mean age of the study population was 22.3±13.2 days at diagnosis. At diagnosis, the mean fT4 was 0.84±0.32 ng/dL, and TSH was 39.3±30 μIU/mL. The mean initial dose of LT4 was 10.9±2.9 μg/kg/day. Overtreatment rates were significantly higher in the highest dose group (12-17 μg/kg/day) compared with the lowest dose group (6-9.9 μg/kg/day) (61.5% and 25%, respectively, p<0.05). None of the patients was undertreated.
  
  
  CONCLUSIONS
  In this study, we found that the rate of overtreatment was significantly higher in patients who were given LT4 doses of 12-17 μg/kg/day. Thus, monitoring thyroid functions earlier than one month of treatment is necessary.
authors.forename: Hale
authors.initials: H
authors.lastname: Tuhan
authors.forename: Ayhan
authors.initials: A
authors.lastname: Abaci
authors.forename: Gizem
authors.initials: G
authors.lastname: Cicek
authors.forename: Ahmet
authors.initials: A
authors.lastname: Anik
authors.forename: Gonul
authors.initials: G
authors.lastname: Catli
authors.forename: Korcan
authors.initials: K
authors.lastname: Demir
authors.forename: Ece
authors.initials: E
authors.lastname: Bober
mesh_terms: D003409:Congenital Hypothyroidism / Q000188:drug therapy*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D008297:Male; D013974:Thyroxine / Q000008:administration & dosage*
chemical_list: D013974:Thyroxine