The action of levothyroxine is...
The action of levothyroxine is identical to the action of natural thyroid hormone - thyroxine which is produced by the thyroid gland. After biotransformation in the body in liothyronine (in the liver and kidneys),
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Generic Eltroxin contains Levothyroxine (L-thyroxine) - a synthetic thyroid hormone; levogyrate isomer of thyroxine (T4);
The action of levothyroxine is identical to the action of natural thyroid hormone - thyroxine which is produced by the thyroid gland. After biotransformation in the body in liothyronine (in the liver and kidneys), it enters the body cells and exert regulatory effect on the development, tissue growth and metabolism. Mechanisms of metabolic effects include receptor binding to the genome, changes in oxidative metabolism in mitochondria and regulation the flow of substrates and actions inside and outside the cells.
In small doses Levothyroxine possesses an anabolic effect.
In medium doses Levothyroxine stimulates growth and development, increases in oxygen demand of tissues, stimulates the metabolism of proteins, fats and carbohydrates, increases the functional activity of the cardiovascular and central nervous systems.
In large doses Levothyroxine inhibits the production of thyrotropin-releasing hormone of the hypothalamus (TTRG) and pituitary thyroid stimulating hormone (TSH).
In hypothyroidism the clinical effect of levothyroxine is observed after 3-5 days, maximum - after 3-4 weeks and persists after withdrawal for 1-3 weeks.
Which is Eltroxin Pharmacokinetics?
After oral administration nearly 80% are absorbed into the blood circulation. Food reduces the absorption of levothyroxine. The maximum plasma concentration is achieved in 6 hours after administration. Levothyroxine binds to plasma proteins (thyroxine binding globulin, thyroxine binding prealbumin and albumin) by 99%. It is distributed in the liver, brain, muscles where Levothyroxine is converted into liothyronine. About 15% of Levothyroxine is excreted by kidneys and bile in unchanged form and as conjugates.
Substitution therapy is absolutely necessary for maintaining normal metabolism in all cases of thyroid function deficiency.
Suppressive therapy is performed after surgery on thyroid gland cancer and radioactive iodine treatment to prevent recurrence of the tumor, as well as in relapse of nodular goiter.
Which is Eltroxin dose?
Daily dose of Eltroxin is indicated individually in dependence of indications, functional condition of thyroid gland, the size of thyroid gland, age, weight, condition of cardiovascular system. Levothyroxine is usually taken once daily in the morning on empty stomach 30 minutes before meal swallowing tablets with a small amount of water without chewing.
Application of Levothyroxine during pregnancy and breastfeeding.
During pregnancy and lactation levothyroxine should be used under medical supervision. Levothyroxine is well researched and there is no reason to assume toxic effects on the fetus or the development of defects.
If you are pregnant, you should continue taking levothyroxine for the treatment of hypothyroidism.
The use of levothyroxine in combination with thyreostatics is contraindicated because it can cause hypothyroidism in the fetus.
Levothyroxine should be used with caution during lactation (breastfeeding).
Levothyroxine is well tolerated and side effects are not common. The use of high-doses of levothyroxine may cause hyperthyroidism symptoms such as tachycardia, arrhythmia, angina (chest pain), tremors, sleep disturbances, insomnia, fatigue, sense of anxiety , increased sweating, hyperhidrosis, loss of body weight (in some cases - a transient increase in body weight due to increased appetite), vomiting, diarrhea, hyperglycemia;
In very rare cases Eltroxin may cause hair loss (alopecia), adrenal insufficiency, impairment of kidney function in children (at high initial doses).
Special warnings and precautions
Eltroxin should be used with caution in patients with cardiovascular diseases (including coronary artery disease, heart failure, hypertension). In these cases, levothyroxine sodium should be used in a low initial dose.
The treatment should be started gradually in elderly patients with prolonged hypothyroidism. An acute adrenal crisis may develop in patients with adrenal insufficiency without adequate maintenance therapy with corticohormons. Eltroxin should be used with caution in patients with diabetes.
In some cases, thyroid hormone can cause or exacerbate pre myasthenic syndrome.
Levothyroxine reduces the effect of insulin and oral antidiabetic drugs.
Levothyroxine reduces the effect of cardiac glycosides.
Levothyroxine increases the effects of antidepressants.
Levothyroxine increases the prothrombin time in concomitant use with oral anticoagulants (coumarin derivatives).
Phenytoin, salicylates, dicumarol, furosemide (in high doses), clofibrate increase the levels of levothyroxine in the blood at the same time may experience arrhythmias.
Cholestyramine, colestipol, sucralfate, aluminum hydroxide (aluminum hydroxide and magnesium), calcium carbonate reduce the absorption of levothyroxine.
Estrogens increase the concentration associated with the thyroglobulin fraction of levothyroxine.
In simultaneous application with chloroquine may increase levothyroxine metabolism, apparently due to induction of chloroquine liver enzymes. Patients receiving Levothyroxine, when applying proguanil or chloroquine may increase the concentration of TSH.
Protein binding of levothyroxine alter anabolic hormons, asparaginase, tamoxifen.
Amiodarone, aminoglutetimid, aminosalicylic acid, etionamid, antithyroid drugs, beta-blockers, carbamazepine, chloral hydrate, diazepam, levodopa, dopamine, metoclopramide, lovastatin, somatostatin, and others may change the levels of thyroid and thyroid-stimulating hormone, usually affecting the synthesis, secretion , distribution, metabolism, action or elimination of thyroid hormones, or altering the secretion of TSH.
Ritonavir may increase the need for levothyroxine dose to achieve the desired effects.
Sertraline in patients with hypothyroidism may decrease the effects of levothyroxine.
Eltroxin should be stored at dry and protected from light place out of reach of children. Do not use the medication after expiration date