Tyroksiini

Tyroksiini, also known as thyroxine or T4, is a thyroid hormone produced naturally by the thyroid gland and used medically as a replacement therapy for hypothyroidism. In the body, T4 largely acts as a prohormone that is converted in tissues to the more active triiodothyronine (T3), which regulates metabolism, growth, and development.

Medical use and mechanism: Tyroksiini is the standard treatment for overt and many cases of subclinical hypothyroidism. The goal of therapy is to normalize thyroid-stimulating hormone (TSH) levels and free T4 to restore normal metabolism. In severe hypothyroidism or life-threatening cases (myxedema coma), intravenous thyroxine may be used.

Pharmacokinetics and dosing: Synthetic thyroxine is typically taken once daily on an empty stomach, as absorption is best without food. The drug has a long half-life of about seven days, with steady state reached after several weeks. Starting doses are usually around 50 mcg daily for most adults, with adjustments based on TSH and free T4 measurements every 4–6 weeks. Elderly patients or those with heart disease often begin at lower doses.

Safety, monitoring, and interactions: Overtreatment can cause symptoms of hyperthyroidism and increases in heart rate, atrial fibrillation, or bone loss. Drug interactions are common; minerals like calcium or iron, and certain medications (e.g., cholestyramine, proton pump inhibitors) can reduce absorption. Changes in thyroid hormone levels can affect anticoagulation therapy, mood, and metabolic parameters. Regular monitoring of TSH and free T4 is recommended, especially during dose changes or pregnancy.

Special considerations: Thyroxine requirements may rise during pregnancy and in recovery from some illnesses. Therapy should be individualized, and patients should report symptoms such as palpitations, anxiety, or weight changes promptly.