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Liotrix is a synthetically derived thyroid hormone replacement preparation. It consists of levothyroxine sodium (thyroxine, T4) and liothyronine sodium (triiodothyronine, T3) in a 4 to 1 ratio by weight. Liotrix was developed when it was believed that serum levels of both T4 and T3 were maintained by direct thyroidal secretion. It is now known that the thyroid gland secretes approximately ten times more T4 than T3 and that 80% of serum T3 is derived from deiodination of T4 in peripheral tissues. Administration of levothyroxine alone is sufficient for maintaining serum T4 and T3 levels in most patients and combination hormone replacement therapy generally offers no therapeutic advantage. In fact, administration of T3 may result in supratherapeutic levels of T3.
Liotrix is a synthetically derived thyroid hormone replacement preparation. It consists of levothyroxine sodium (thyroxine, T4) and liothyronine sodium (triiodothyronine, T3) in a 4 to 1 ratio by weight. Liotrix was developed when it was believed that serum levels of both T4 and T3 were maintained by direct thyroidal secretion. It is now known that the thyroid gland secretes approximately ten times more T4 than T3 and that 80% of serum T3 is derived from deiodination of T4 in peripheral tissues. Administration of levothyroxine alone is sufficient for maintaining serum T4 and T3 levels in most patients and combination hormone replacement therapy generally offers no therapeutic advantage. In fact, administration of T3 may result in supratherapeutic levels of T3.
The hormones, T and T, are tyrosine-based hormones produced by the thyroid gland. Iodine is an important component in their synthesis. The major secreted form of thyroid hormone is T4. T4 is converted T3, the more active thyroid hormone, by deiodinases in peripheral tissues. T3 acts in the body to increase basal metabolic rate, alter protein synthesis and increase the body's sensitivity to catecholamines (such as adrenaline). Thyroid hormones are essential for proper development and differentiation of all cells of the human body. T and T regulate protein, fat and carbohydrate metabolism to varying extents. The most pronounced effect of the hormones is in altering how human cells use energetic compounds. The thyroid hormone derivatives bind to the thyroid hormone receptors initially to initiate their downstream effects.
May be used to treat primary, secondary or tertiary hypothyroidism. May also be used to suppress thyroid stimulating hormone (TSH) secretion in patients with simple (nontoxic) goiter, subacute or chronic lymphocytic thyroiditis multinodular goiter, and in the management of thyroid cancer. May be used in conjunction with other antithyroid agents to treat thyrotoxicosis to prevent goitrogenesis and hypothyroidism. May also be used for differential diagnosis of suspected mild hyperthyroidism or thyroid gland autonomy.
