Abstract
In Britain in 1980 the bio-availability of L.Thyroxine was increased by 11%. Treatment of 13 hypothyroid children (7congenital, 6 juvenile. (3 - 16 years) was reassessed using a highly sensitive assay of T.S.H. T3, T4, Free T3 + Free T4.
At the beginning of the study 12 children had T.S.H. below the upper limit of normal (< 5 MU/L). At intervals of 4 weeks L Thyroxine was reduced by 12.5 ug until the T.S.H. was elevated above normal. The one child with an elevated T.S.H. had L. Thyroxine increased by 12.5 ug at 4 weekly intervals until the T.S.H. fell into the normal range (0.3-5 MU/L). The optimal dose was defined as the minmm dose to maintain T.S.H. < 5 MU/L.
Mean dose at start of study 108.5± 4.7 ug/M2/day/3.8±.18 ug/kg/day. Mean optimal dose was 92.5 ± 4.0 ug/M2day/3.24 ± 0.13 ug/kg/day. There was no difference in optimal dosage in congenital or juvenile cases. Optimal dose correlated strongly with both surface area (r = 0.98) and weight (r = 0.97). Some children had subtle behavioural signs of over-treatment initially; in none was bone age advanced. Mean values for T3, T4, Free T3 + Free T4 all fell at the upper limit of the normal range on both initial and optiral dosage.
We conclude that current dosage recommendations for L. Thyroxine may be too high and highly sensitive T.S.H. assay assist in titration of dosage.
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Hodges, S., O'Malley, B. & Swift, P. OPTIMAL DAILY DOSAGE OF THYROXINE IN CHILDHOOD: A REAPPRAISAL. Pediatr Res 23, 133 (1988). https://doi.org/10.1203/00006450-198801000-00194
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DOI: https://doi.org/10.1203/00006450-198801000-00194