TARGETED LEVOTHYROXINE THERAPY FOR TREATMENT OF CONGENITAL HYPOTHYROIDISM.

OBJECTIVE: The purpose of this study was to determine if infants with congenital hypothyroidism (CH) whose initial dose of levothyroxine (LT4) is based on thyroid gland anatomy require fewer dose adjustments in the first 6 months of life than those who were started empirically on LT4.

METHODS: Newborns with CH who had a thyroid ultrasound performed at diagnosis were eligible for this prospective, historical case-controlled study. The daily LT4 dose prescribed was based on results on the thyroid ultrasound as follows: 15 mcg/kg for athyreosis, 12 mcg/kg for a dysgenetic thyroid, and 10 mcg/kg for an anatomically normal gland. Routine labs according to standard guidelines were obtained, and the number of dose adjustments over the first 6 months of therapy was recorded. Each study participant was matched with 2 historical controls with CH based on sex and thyroid anatomy.

RESULTS: Twenty-two subjects (10 with athyreosis, 4 with dysgenetic glands, and 8 with anatomically normal glands) were matched to 44 controls. There was no significant difference in the overall number of adjustments in the study group compared to controls (P = .74). However, there were significantly fewer adjustments made for undertreatment (P = .03) and significantly more adjustments made for overtreatment (P = .006) in subjects with athyreosis compared to controls.

CONCLUSION: Targeted LT4 therapy does not appear to decrease the overall frequency of dose adjustments for infants with CH. However, 15 mcg/kg/day appears to exceed thyroid hormone requirements in infants with CH due to athyreosis.

ABBREVIATIONS: CH = congenital hypothyroidism LT4 = levothyroxine OT = overtreatment T4 = thyroxine TSH = thyroid-stimulating hormone UT = undertreatment.