-2%
Thyrox contains Levothyroxine Sodium, a synthetic version of the naturally occurring hormone T4, secreted by the thyroid gland. In the body, around 30% of T4 is converted to the more active form, Triiodothyronine (T3). Most T4 binds to Thyroxine-Binding Globulin (TBG), prolonging its half-life. Only a tiny fraction (~0.03%) remains unbound and active.
Elimination half-life: 6–7 days (shorter in hyperthyroidism, longer in hypothyroidism).
Metabolism: Mainly in the liver with enterohepatic recycling.
A single daily dose is typically sufficient to maintain stable T3 levels.
- Used as replacement therapy in all forms of hypothyroidism except transient cases during recovery from subacute thyroiditis.
- For TSH suppression in patients with goitre, thyroid nodules, or post-treatment of thyroid cancer.
- To counteract the goitrogenic effects of certain medications, such as lithium.
- As a diagnostic agent in thyroid suppression testing.