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 5-7μg/kg/day, which was higher than a level of 2-4μg/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.