medwireNews: Children using an oral solution of levo-thyroxine (L-T4) for treatment of congenital hypothyroidism may require closer monitoring during the first few months than those using tablet formulations, say researchers.

Although the study participants largely achieved thyroid-stimulating hormone levels within the target range, significantly more of the children taking L-T4 solution than those taking tablets had levels lower than 0.5 mUI/L at 1 and 6 months, at 57% versus 38% and 47% versus 33%, respectively.

And at 1 month, 37.4% of those taking the solution versus 24.2% of those taking tablets had free thyroxine levels higher than 2.2 ng/dL, which was also a significant difference.

This indicates “a higher risk of overtreatment during the first months of therapy probably due to a higher absorption of the liquid L-T4 than the tablet form”, say Maria Cristina Vigone (Vita-Salute San Raffaele University, Milan, Italy) and study co-authors.

Overtreatment is associated with behavioural problems and impaired cognitive development, they note.

The team therefore recommends reduced starting doses for children taking L-T4 solution, of 8–13 µg/kg per day, with a follow-up interval of less than 15 days.

The median starting dose in the study was 11.24 μg/kg per day for the 117 children using L-T4 solution and 11.16 μg/kg per day for the 137 taking tablets, with an overall range of 3.50–15.67 μg/kg per day.

The children were monitored up until the age of 3 years, and outcomes over the full follow-up period were generally similar with both L-T4 formulations, which the researchers say confirms their efficacy in a study that is markedly larger and longer than previous ones.

“Therefore, no need for closer dose adjustment or difference in therapeutic approach would seem to be required after 3 months of follow-up when using the liquid formulation,” they write in the European Journal of Endocrinology.

The researchers note that the presence of ethanol in the L-T4 solution is somewhat controversial, despite the maximum amount potentially ingested being well within what is regarded as the safe limit for chronic use.

They found that growth was similar between the two treatment groups, and all developmental scores were within normal parameters. However, Developmental Quotient scores tended to be lower for children taking solution rather than tablets, with these differences attaining significance for language at 1 year and hand–eye coordination at 3 years.

“Further assessment will be necessary to validate these data, specifically concerning the effects of prolonged chronic exposure to ethanol, the greater tendency to iatrogenic hyperthyroidism during the first months of life with oral solution, the severity of [congenital hypothyroidism] and the parental level of education and bilingualism”, the team concludes.

By Eleanor McDermid

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Eur J Endocrinol 2021; doi:10.1530/EJE-20-1444

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