Levothyroxine sodium is indicated for the treatment of hypothyroid conditions of various etiologies, including those which are medically and surgically affected. The drug is prescribed for the prevention and treatment of euthyroid diffuse goiter, toxic diffuse goiter, and congenital functional deficiency of the thyroid gland.
Levothyroxine sodium is a generic version of Synthroid® – prescribed drug well-known in the USA, Canada and UK.
Levothyroxine is also used in complex therapy to prevent the recurrence of nodular malignant thyroid formations after surgery. The drug is prescribed as an additional component for differential diagnostic tests in which suppression of thyroid function is required. Levothyroxine is used in the complex treatment of Graves’ disease and euthyroid hyperplasia of the thyroid gland.
Levothyroxine sodium tablets are intended for oral administration. It should be taken on an empty stomach, preferably in the morning with water. The daily dose is prescribed strictly individually depending on the form of the disease, the severity of its course and indications. In hypothyroidism, the initial dose is 50–100 mcg, with a transition to the supporting dose, 125–250 mcg. In cases of congenital hypothyroidism, 8–10 mcg per kg of weight per day for babies up to six months of age is recommended, while for those 6–12 months of age, 6–8 mcg per kg of weight per day is generally prescribed. For treatment of endemic goiter, first 50 mcg per day is recommended, and after that 100–200 mcg. For euthyroid goiter, 100–200 mcg per day is prescribed.
Levothyroxine is not indicated in hyperthyroidism of any etiology or hypersensitivity to the drug. Also, patients with adrenocortical insufficiency and acute myocardial infarction should not take the drug. It is contraindicated to take in pregnancy, along with thyreostatics, since the active substance (levothyroxine sodium) reduces their effectiveness, and high doses of thyreostatics can lead to the onset of a baby’s congenital hypothyroidism. It is necessary to know that the drug in complex therapy with antidepressants and anticoagulants significantly enhances the effect of these drugs.
Levothyroxine Side effects
Levothyroxine can cause the following side effects: anxiety, heart rhythm disturbance, chest pain, diarrhea, hyperhidrosis, alopecia, decreased adrenal function, and tremors; in children – renal function impairment; allergic reactions – itching, skin rash.
Levothyroxine does not cause significant weight loss in most people.
In cases of drug overdose, thyrotoxic crisis may occur, which can be delayed for a few days. Symptomatic therapy includes beta-adrenoblockers, corticosteroids, and plasmapheresis.
The drug is almost 80% absorbed in the upper parts of the small intestine; intake of food decreases absorption. The maximum level of the active substance in the blood plasma is observed after 5–6 hours. Levothyroxine is metabolized mainly in the liver, muscles, brain, and kidneys. It is excreted from the body in the form of metabolites with urine and bile.
The half-life is 6–7 days. The therapeutic effect begins to manifest itself after 3–5 days of taking the drug. Early hyperplastic diffuse goiter disappears or decreases significantly during 3–6 months of taking the drug. In the later stages of the disease, a significant reduction in the size of the thyroid gland occurs in more than 30% of cases.
The drug is prescribed with caution for diseases of the cardiovascular system. In such cases, patients should begin to take a low initial dose of Levothyroxine with a gradual increase. Treatment should be started gradually with a prolonged course of hypothyroidism.
In patients with adrenocortical insufficiency, an acute adrenal crisis is possible. Therefore, adequate support for corticosteroids is required. The drug is administered with caution in case of diabetes insipidus. In patients with diabetes mellitus, when performing a differential diagnostic test for thyroid suppression, it is recommended to increase the doses of antidiabetic drugs.
Pregnancy and breastfeeding
Use during pregnancy and lactation requires the supervision of a doctor. It is forbidden to use the drug together with thyreostatic drugs in connection with the risk of hypothyroidism in the fetus.
Levothyroxine for children
This drug can be taken by children after six months of age.
In the elderly
With prolonged treatment of hypothyroidism in elderly patients, the drug should be taken gradually.
The drug potentiates the effect of indirect anticoagulants and reduces the effectiveness of hypoglycemic peroral drugs. Salicylates, dicoumarol, furosemide, and clofibrate can displace levothyroxine from its connection with plasma proteins. Sucralfate, aluminum hydroxide, calcium carbonate, and cholestyramine reduce the absorption of levothyroxine from the gastrointestinal tract.
In combination with ritonavir, the need for levothyroxine may increase. When combined with sertraline, there may be a decrease in the effects of levothyroxine sodium.
With the rapid intravenous administration of phenytoin against the background of levothyroxine therapy, the concentration of free levothyroxine in the blood plasma may increase, which can cause arrhythmia. The combination with chloroquine causes an increase in the metabolism of levothyroxine. In combination with proguanil or chloroquine, an increase in the concentration of thyroid-stimulating hormones is possible.