Initial treatment dose of L-thyroxine in congenital hypothyroidism

Karin A. Selva, Scott H. Mandel, Leanne Rien, David Sesser, Richard Miyahira, Michael Skeels, Jerald C. Nelson, Stephen H. LaFranchi

Research output: Contribution to journalArticlepeer-review

73 Scopus citations


Objectives: To determine the optimal initial treatment dose of L-thyroxine in congenital hypothyroidism (CH) by evaluating the rime course of rise of thyroxine (T4) and free T4 concentrations into an established "target range" and normalization of thyroid-stimulating hormone (TSH) and to reevaluate the "target range" for T4 and free T4 concentrations during the first 2 weeks of CH treatment. Study design: Infants of birth weight 3 to 4 kg with CH (n = 47) detected by newborn screening were randomly assigned into three L-thyroxine treatment dose arms: 37.5 μg/day (group 1); 62.5 μg/day for 3 days, then 37.5 μg/day (group 2); and 50 μg/day (group 3). Serum T4, free T4, triiodothyronine (T3), free T3, and TSH were measured before treatment and at 3 days and 1, 2, 4, 8, and 12 weeks after treatment. Results: T4 and free T4 concentrations increased into the target range (10 to 16 μg/dL) by 3 days of therapy in infants in groups 2 and 3 and by 1 week in group 1; 50 μg/day (average 14.5 μg/kg/day) provided the most rapid normalization of TSH by 2 weeks. With the use of linear regression analysis of T4 versus TSH or free T4 versus TSH plots, the intercept at the lower range of normal for TSH (1.7 mU/L) showed T4 = 19.5 μg/dL and free T4 = 5.23 ng/dL. Conclusions: Initial dosing of 50 μg/day (12-17 μg/kg per day) raised serum T4 and free T4 concentrations to target range by 3 days and normalized TSH by 2 weeks of therapy. We recommend consideration of a somewhat higher "target range" of 10 to 18 μg/dL for T4 and 2 to 5.0 ng/dL for free T4 during the first 2 weeks of L-thyroxine treatment. After 2 weeks of treatment, the target range drops to 10 to 16 μg/dL for T4 and 1.6 to 2.2 for free T4.

Original languageEnglish (US)
Pages (from-to)786-792
Number of pages7
JournalJournal of Pediatrics
Issue number6
StatePublished - Dec 1 2002

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health


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