Levothyroxine sodium is used as replacement or supplemental therapy in congenital or acquired hypothyroidism of any etiology, except transient hypothyroidism during the recovery phase of subacute thyroiditis. Levothyroxine sodium is specifically indicated for use in the management of subclinical hypothyroidism and primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) hypothyroidism. Primary hypothyroidism may result from functional deficiency, primary atrophy, partial or complete absence of the thyroid gland, or from the effects of surgery, radiation, or antithyroid agents, with or without the presence of goiter.
Replacement therapy with levothyroxine sodium must be maintained continuously to control the symptoms of hypothyroidism. Levothyroxine sodium generally is the preferred thyroid agent for replacement therapy because its hormonal content is standardized and its effect is therefore predictable.
Levothyroxine sodium also is considered the drug of choice for the treatment of congenital hypothyroidism (cretinism). For a discussion on the use of levothyroxine in the treatment of congenital hypothyroidism,
Levothyroxine sodium IV injection is used in the treatment of myxedema coma. Levothyroxine sodium injection has been used in other conditions when rapid thyroid replacement is required; however, this is not an FDA-labeled use for the currently available injection.
Levothyroxine sodium may be used with antithyroid agents in the treatment of thyrotoxicosis to prevent goitrogenesis and hypothyroidism. While administration of levothyroxine occasionally may be useful to prevent antithyroid agent-induced hypothyroidism in the management of thyrotoxicosis during pregnancy, combination therapy generally is considered unnecessary since it may increase the requirement for antithyroid agents and therefore the risk of fetal hypothyroidism, which is not amenable to exogenous thyroid agent therapy.
Pituitary TSH Suppression
Levothyroxine sodium may be used to suppress the secretion of thyrotropin (thyroid-stimulating hormone, TSH) in the treatment or prevention of various types of euthyroid goiters, including thyroid nodules, subacute or chronic lymphocytic thyroiditis (Hashimoto's thyroiditis), and multinodular goiter. Levothyroxine sodium also is used as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated (papillary and follicular) thyroid cancer.