Abstract
Levothyroxine is a synthetic levoisomer of thyroxine. Currently, it is one of the most commonly prescribed drugs worldwide.
The main indication for levothyroxine treatment is hypothyroidism of any type. It is also used for suppression therapy in patients with thyroid cancer.
The therapeutic dose depends on the residual thyroid secretion, the weight of the patient, and the purpose of the treatment. The initial dose typically ranges from 25 to 50 μg daily, with further adjustment according to the level of thyroid-stimulating hormone (TSH).
Initial dose titration is not recommended during postoperative replacement therapy and in pregnant women with hypothyroidism. Most of the plasma thyroxine is bound to transport proteins.
However, only the free thyroxin is biologically active. Thyroxine is mainly a prohormone which is metabolized to the more active triiodothyronine.
Properly managed levothyroxine treatment is safe with minimal adverse effects. Palpitations and other symptoms of hyperthyroidism may occur with overdose.
For proper absorption, levothyroxine should be taken on an empty stomach, separately from other medications, at least 30 minutes before breakfast. Absorption may be impaired by other medications, especially by those increasing the pH of gastric acid.