Comparison between Liquid and Tablet Formulations of Levothyroxine in the Initial Treatment of Congenital Hypothyroidism

OBJECTIVE: To evaluate the effects of liquid (drops) and tablet formulations of levothyroxine in homogeneous groups of infants with congenital hypothyroidism (CH) as diagnosed through neonatal screening. STUDY DESIGN: Forty-two consecutive infants with CH were subdivided into 2 groups consisting of infants with the severe or the moderate/mild form. For each form, the infants with CH were randomly assigned to receive liquid (group 1) or tablet (group 2) formulation. In all patients, thyroid function tests were performed before the beginning of therapy and at 15 and 30 days and at 3 and 6 months after the beginning of therapy. RESULTS: In the severe form, after 15 days of treatment, serum thyrotropin (TSH) levels became normal in 8 of 9 patients in group 1 and in 5 of 9 patients in group 2; serum free triiodothyronine (fT3) levels were significantly higher in group 1 than in group 2; and serum fT4 levels were higher than the upper limit of the normal range in all patients in both groups. During the follow-up, there were significantly more patients with suppressed TSH concentrations in group 1 than in group 2. In the moderate/mild form, the patients of group 1 and group 2 showed median values of TSH, fT3, and fT4 that were not significantly different. No clinical or electrocardiographic signs of heart disease were found. There were no significant differences in the developmental quotient between group 1 and group 2 patients with severe and moderate/mild CH. CONCLUSIONS: Our data seem to indicate that there is not complete bioequivalence between drops and tablets, especially in infants with severe CH.