Evaluation of L-thyroxine requirement in treatment of congenital hypothyroidism

The optimal daily requirement of L-T4 in replacement therapy for hypothyroidism was evaluated in evaluated in 24 cases of congenital hypothyroidism and 3 of juvenile myxedema, ranging from 3 to 30 years of age. The optimal dose of L-T4, defined as the minimal dose necessary to suppress the serum concentration of TSH into the normal range, was determined in each patient. The optimal dose of L-T4 between 3 and 5 years of age was 5-7 microgram/kg/day, which was higher than a level of 2-4 microgram/kg/day in adult. All patients appeared clinically euthyroid, and their serum concentration of T4 and T3 remained within the normal range while the optimal dose of L-T4 was being administered. These observations imply that physiologic requirement of L-T4 are lower than previously recommended dosages. Further studies to establish more precise therapeutic guidelines are needed.