Description
L-Tyroxine Pharmacodynamics
The active substance of the drug L-thyroxine – sodium levothyroxine is a synthetic left-handed isomer of thyroxine, which in its effect is identical to the natural thyroid hormone synthesized by the human thyroid gland. After partial conversion to triiodothyronine (Tz) in the liver and kidneys and transfer to body cells, sodium levothyroxine influences tissue development and growth and metabolism. In low doses it has an anabolic effect on protein and fat metabolism. In medium daily doses it stimulates growth and development, increases tissue oxygen demand, stimulates metabolism of proteins, fats and carbohydrates, increases the functional activity of the cardiovascular system and the central nervous system. At high doses, sodium levothyroxine inhibits the production of thyrotropin-releasing hormone of the hypothalamus and thyrotropic hormone (TSH) of the pituitary gland. The therapeutic effect is observed 7-12 days after the start of use, the effect of the drug after its withdrawal lasts for the same time. Clinical effect in hypothyroidism is seen after 3-5 days. Diffuse goiter decreases or disappears within 3-6 months of using the drug.
Indications
– hypothyroidism;
– euthyroid goiter;
– As a substitute therapy and for prevention of goiter recurrence after surgical operations on the thyroid gland;
– As a suppressive and substitution therapy for malignant tumors of the thyroid gland, mainly after surgical treatment;
– diffuse toxic goiter: after achieving an euthyroid state with antithyroid drugs (in the form of combination or monotherapy);
– As a diagnostic aid in the thyroid suppression test
Contraindications
– Hypersensitivity to sodium levothyroxine and/or any excipient of the drug
– untreated thyrotoxicosis;
– untreated pituitary insufficiency;
– untreated adrenal insufficiency;
– Use in combination with antithyroid drugs during pregnancy;
– lactose intolerance, lactase deficiency, glucose-galactose malabsorption syndrome.
Do not start treatment with the drug in the presence of acute myocardial infarction, acute myocarditis, acute pancarditis.
Dosage and administration
- The daily dose is determined individually, depending on the indications, the clinical condition of the patient and the data of laboratory examination.
- Daily dose of levothyroxine sodium is taken orally in the morning on an empty stomach at least 30 min before a meal, followed by a small amount of liquid (half a glass of water) and without chewing.
- During substitution therapy of hypothyroidism in patients younger than 55 years old in absence of cardiovascular diseases, sodium levothyroxine is used in a daily dose of 1.6-1.8 mkg/kg of body weight; in patients older than 55 years or with cardiovascular diseases – 0.9 mkg/kg of body weight.
- Initial phase of replacement therapy for hypothyroidism
- Patients without cardiovascular diseases under 55 years of age
– The initial dose: women – 75-100 mcg/day, men – 100-150 mcg/day. - Patients with cardiovascular disease or older than 55 years
– The starting dose is 25 micrograms per day.
– Increase the dosage by 25 mcg at 1-month intervals until the TTH level in the blood is normalized.
– If cardiovascular symptoms appear or worsen, adjust the cardiovascular therapy
Recommended doses of levothyroxine sodium for treatment of congenital hypothyroidism
Age Daily dose (mcg) Dose per body weight (mcg/kg)
0-6 months 25-50 10-15
6-12 months 50-75 6-8
1-5 years 75-100 5-6
6-12 years 100-150 4-5
> 12 years 100-200 2-3 - Indications Recommended doses of sodium levothyroxine (mcg/day)
- Treatment of euthyroid goiter 75-200
- Prevention of relapse after surgical treatment of euthyroid goiter 75-200
- In the complex treatment of thyrotoxicosis 50-100
- Thyroid cancer suppressive therapy 150-300
- Thyroid suppression test 4 weeks before test 3 weeks before test 2 weeks before test 1 week before test
75 mcg/d 75 mcg/d 150-200 mcg/d 150- 200 mcg/d
Infants and children less than 3 years of age should receive a single daily dose of levothyroxine sodium 30 minutes before their first feeding. The tablet is dissolved in water to a fine suspension, which is prepared immediately before taking the drug. - In patients with severe long-term hypothyroidism treatment should be started with extreme caution, with low doses – from 12.5 mcg/day, the dose is increased to maintenance at longer intervals – by 12.5 mcg/day every 2 weeks and the blood TSH concentration is determined more frequently.
- For hypothyroidism, levothyroxine sodium is usually taken for life. At thyrotoxicosis levothyroxine sodium is used in complex therapy with antithyroid drugs after achievement of euthyroid condition. In all cases, the duration of treatment with the drug is determined by the doctor.
- For accurate dosing, the most appropriate dosage of sodium levothyroxine should be used.
