Safety of medications and hormones used in the treatment of pediatric thyroid disorders.

Levo-thyroxine (L-T4) is used to treat children with any form of hypothyroidism. In fact, L-T4 is the natural hormone and the principal product secreted by the thyroid. It is then converted into T3, the active compound at the tissue level, according to the temporary needs of the organism. Therefore, L-T4 can replace thyroid function in hypothyroid patients on a physiological basis. L-T4 administration is a safe and beneficial treatment that can be easily monitored by the concomitant measurement of TSH and free thyroid hormone levels. Antithyroid drugs (methimazole [MMI], carbimazole [CMI] and propylthiouracil [PTU]) are the initial treatment of choice for most children with hyperthyroidism, which is most commonly caused by Graves' disease. While generally similar in efficacy and safety, there are some differences. MMI and CMI have a longer half-life and so can be given once daily, improving compliance in children. At low doses, there are fewer side effects with MMI and CMI compared to PTU. Drug-related hepatitis and vasculitis are almost exclusively seen with PTU. Beta-adrenergic antagonists are safe adjunctive therapy. In specific situations, e.g., in preparing for thyroid surgery, iodine for a limited time is used to inhibit thyroid hormone secretion and reduce gland vascularity.