Levothyroxine is a synthetic thyroid hormone, identical to thyroxine (T4) that is produced and released by the thyroid gland. In the peripheral tissues, T4 is converted to T3, the active metabolite, by deiodination. T3 and T4 diffuses into the cell nucleus and bind to the thyroid receptors attached to DNA. This activates gene transcription and synthesis of mRNA and cytoplasmic proteins. Thus thyroid hormones regulate multiple metabolic processes and play an essential role in normal growth and development, and maturation of CNS and bone. Levothyroxine is effective as replacement or supplemental therapy in natural thyroxine deficiency.
