Initial treatment dose of L-thyroxine in congenital hypothyroidism

Objectives: To determine the optimal initial treatment dose of L-thyroxine in congenital hypothyroidism (CH) by evaluating the time 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...

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Published inThe Journal of pediatrics Vol. 141; no. 6; pp. 786 - 792
Main Authors Selva, Karin A., Mandel, Scott H., Rien, Leanne, Sesser, David, Miyahira, Richard, Skeels, Michael, Nelson, Jerald C., LaFranchi, Stephen H.
Format Journal Article
LanguageEnglish
Published New York, NY Mosby, Inc 01.12.2002
Elsevier
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Summary:Objectives: To determine the optimal initial treatment dose of L-thyroxine in congenital hypothyroidism (CH) by evaluating the time 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. (J Pediatr 2002;141:786-92)
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ISSN:0022-3476
1097-6833
DOI:10.1067/mpd.2002.128887