Levothyroxine Use in Infants and Children with Congenital or Acquired Hypothyroidism

Contributing Editor: Marcia L. Buck, Pharm.D.; Editorial Board: Kristi N. Hofer, Pharm.D.; Michelle W. McCarthy, Pharm.D.

Disclosures

Pediatr Pharm. 2008;14(10) 

In This Article

Dosing Recommendations

Levothyroxine is administered as a single daily dose. It is recommended that oral doses be given in the morning on an empty stomach, ideally 30 minutes to 1 hour before breakfast. For older adolescents and adults requiring full replacement, the oral dose is approximately 1.7 mcg/kg/day, with a usual daily dose of 100 to 125 mcg. Doses greater than 200 mcg/day are not typically necessary.[2,3,5]

In newborns, the recommended oral dose is 10 to 15 mcg/kg/day or approximately 25 mcg/day. Infants with cardiac disease should start at a lower dose. In older infants and children, the following table may be used as a guide for the initial dose:

 

 

Parenteral levothyroxine may be administered intramuscularly or intravenously. The initial parenteral dose should be one-half of the oral dose. Further adjustments should be guided by serum thyroid function tests.[2,3,5]

Total or free serum T4 and TSH should be monitored on a routine basis in infants and children taking levothyroxine. It is recommended that T4 be maintained in the upper half of the normal range. Serum TSH should be kept below 20 mUnit/L, but may remain elevated in infants with congenital hypothyroidism for a prolonged period after therapy has been initiated. Levels should be obtained at 2 and 4 weeks after the start of treatment, then every 1 to 2 months during the first year of life. Monitoring should be done every 2 to 4 months in children between 1 and 3 years of age. After that point, the manufacturer recommends that routine monitoring be done every 3 to 12 months.[2,3]

Recent guidelines from the American Academy of Pediatrics, the American Thyroid Association, and the Lawson Wilkins Pediatric Endocrine Society suggest that monitoring every 6 to 12 months is adequate for children with congenital hypothyroidism over 3 years of age in whom previous levels have been satisfactory. The authors also recommend that free T4 and TSH levels be obtained 4 weeks after any change in levothyroxine dose.[5]

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