Synthroid (Levothyroxine) Medication


synthroid levothyroxine medication used to treat disorders of the thyroid gland and obesitySynthroid is the most commonly used name for levothyroxine sodium. In particular, it is a thyroid hormone produced synthetically, which has the same effect as the endogenous hormone thyroxine-4 (T-4). Hormones of the thyroid gland are responsible, mainly, for regulating the metabolic rate and play an important role for the human body. When hormonal thyroid medications are prescribed, the metabolism is markedly improved. This manifests itself in a more rapid transformation of carbohydrates, proteins and fats, as the body burns more calories per day. For medical purposes, these hormones are used to treat disorders of the thyroid gland and obesity (caused by such a violation).

What is Synthroid?

Levothyroxine, a thyroid hormone, is used to treat hypothyroidism, a condition in which the thyroid gland does not produce enough thyroid hormone. Without this hormone, the body can not function properly, as a result: poor growth; slow speech; lack of energy; weight gain; hair loss; dry, thick skin; and hypersensitivity to cold. When taken correctly, levothyroxine changes these symptoms. Levothyroxine is also used to treat congenital hypothyroidism and goiter (enlargement of the thyroid gland).

How Does Synthroid Work? Mechanisms of metabolic effectsIt is used in case of hypothyroid conditions of different etiology (including those caused by surgical or medicamental effects), prevention of recurrence of nodular goiter after resection of the thyroid gland, diffuse euthyroid goiter; diffuse toxic goiter – after the creation of an euthyroid state by thyreostatics (in the form of combined or monotherapy); thyroid cancer after surgical treatment (to suppress tumor recurrence and as a substitute therapy), as a diagnostic tool in the test of thyroid suppression. As a part of complex therapy: Graves disease, autoimmune thyroiditis.

How Does Synthroid Work?

Mechanisms of metabolic effects include receptor binding to the genome, changes in oxidative metabolism in the mitochondria, and regulation of the flow of substrates and cations both inside and outside the cell. In small doses, it has an anabolic effect, in the middle – it stimulates growth and development, increases the oxygen demand of tissues, regulates the metabolism of proteins, fats and carbohydrates, increases the functional activity of the cardiovascular system and the central nervous system, in large – inhibits the production of thyrotropin-releasing hormone of the hypothalamus and thyroid-stimulating hormone of the pituitary gland.

If ingested, 80% of the dose taken is absorbed almost exclusively in the upper part of the small intestine, eating reduces absorption. Cmax in the blood serum is achieved approximately 5-6 hours after administration. Binding to whey proteins (thyroxin-binding globulin, thyroxine-binding prealbumin and albumin) is more than 99%. In various tissues, monoiodiodization of sodium levothyroxine occurs with the formation of triiodothyronine (T3) and inactive products. Thyroid hormones are metabolized mainly in the liver, kidneys, brain and muscles. A small amount is subjected to deamination and decarboxylation, as well as conjugation with sulfuric and glucuronic acids (in the liver). Metabolites are excreted in urine and bile. T1 / 2 – 6-7 days. With thyrotoxicosis, T1 / 2 is shortened to 3-4 days, with hypothyroidism extended to 9-10 days.

The clinical effect with hypothyroidism manifests itself in 3-5 days. Early diffuse hyperplastic goiter decreases or disappears within 3-6 months, at late nodal stages a significant reduction in thyroid size is observed only in 30% of cases, but almost all patients are prevented from further growth.

Safety Information

Synthroid levothyroxine safety informationBefore taking levothyroxine, tell your doctor and pharmacist if you are allergic to levothyroxine, thyroid hormone, other drugs, or any of the ingredients in levothyroxine. Ask your pharmacist for a list of ingredients. Tell your doctor and pharmacist that prescription and over-the-counter medications you are taking, in particular

  • Amphetamines;
  • Anticoagulants (“blood solvents”), such as Warfarin (Coumadin);
  • Antidepressants or sedatives;
  • Arthritis medicine;
  • Aspirin;
  • Beta-blockers, such as Metoprolol (Lopressor, Toprol), Propranolol (Anaprilin) or Timolol (Blocadren, Timoptic);
  • Chemotherapy for cancer agents;
  • Diabetes drugs (insulin and tablets);
  • Digoxin (Lanoxin);
  • Estrogens;
  • Methadone;
  • Oral contraceptives;
  • Phenytoin (Dilantin);
  • Steroids;
  • Theophylline (TheoDur);
  • and vitamins.

If you take antacids, calcium carbonate (Tums), Cholestyramine (Questran), Colestipol (Colestid), Iron, Orlistat (Alli), Simethicone (Phazyme, Gas X), Polystyrene sodium sulfonate (Kayexalate), or Sucralfate (Carafate) , take it at least 4 hours before or 4 hours after taking levothyroxine. Tell your doctor if you have or have ever had:

  • diabetes;
  • hardening of the arteries (atherosclerosis);
  • kidney disease;
  • hepatitis;
  • cardiovascular diseases such as high blood pressure,
  • chest pain (angina pectoris),
  • arrhythmia, or heart attack; or a decreased adrenal or pituitary gland.
  • if you have surgery, including dental surgery, tell the doctor or dentist that you are taking levothyroxine.

Restrictions on the use: CHD (atherosclerosis, stenocardia, myocardial infarction in history), arterial hypertension, arrhythmia, sugar and diabetes insipidus, severe long-term hypothyroidism, malabsorption syndrome (dose adjustment may be required), pituitary insufficiency, elderly age.


The drug has no embryotoxic, teratogenic and mutagenic effects. It poorly penetrates the placental barrier. In small doses, it penetrates into breast milk, even with high-dose therapy. In the second and third trimester of pregnancy the need for thyroid hormones increases, therefore it is necessary to inform the attending physician about pregnancy for possible correction of the doses of the drug.

The use of the drug in a combination with thyreostatic drugs during pregnancy and lactation is not recommended, because of this, the child may develop hypothyroidism, only monotherapy with levothyroxine is indicated.

Be careful if taking other drugs together with Synthroid:

  • The drug reduces the effect of insulin and oral antidiabetic drugs, so when prescribing levothyroxine to patients with diabetes, it is necessary to monitor blood sugar and, if necessary, adjust the dose of insulin or oral antidiabetics.
  • With simultaneous intake of the drug reduces the effect of cardiac glycosides.
  • The drug enhances the pharmacological effect of antidepressants.
  • Levothyroxine is able to increase prothrombin time when taken together with anticoagulants, especially this interaction is expressed with coumarin derivatives.
  • Estrogens reduce the effectiveness of levothyroxine.

About Synthroid Dosing

Synthroid dosageAs with all drugs of the thyroid gland, the dose should be increased gradually. Usually, athletes start with a dose of 25-100 mg and slowly increase to 25-50 mg every day or every other day. The last dose should not exceed 200-400 mg ). With thyroid hormone drugs, there is always the risk of changing the metabolic process when consuming an excessively high dose or with long use.

You need to be careful not to exceed the dose and not take the drug for more than 6-8 weeks. For the same reason, it is important to reduce the dose at the end of the cycle gradually, as well as increase. It is recommended to reduce the dose by 25-50 mg after 1 or 2 days. The body will get used to the change in the hormonal level, and you will avoid the “shock” that is possible with a sharp cessation.

Manifestations of an overdose can appear immediately after taking or a few days later. When an overdose of the drug there are symptoms of thyrotoxicosis, in severe cases right up to thyrotoxic crisis. They are characterized by a palpitation, diarrhea, pain in the epigastric region, tachycardia, attacks of stenocardia. There are also manifestations of heart failure, tremor, disturbances in sleep and wakefulness, fever, heat intolerance, increased sweating, and increased irritability. The laboratory indicators of the free thyroxine index and the level of T3 and T4 are increasing. There may be a decrease in body weight.

Treatment consists in the cancellation of the drug. In acute overdose, intramuscular injection of glucocorticosteroids (Prednisolone, hydrocortisone, dexamethasone) or the administration of B-adrenoblockers is indicated. In critical cases, when poisoning with levothyroxine, plasmapheresis is indicated.

What Forms Does the Medication Come in?

Synthroid tablets formsThere are tablets of different dosages. 1 tablet contains:

  • Levothyroxine (Synthroid) – 25, 50, 75, 100, 125 and 200 mcg;
  • Excipients, including lactose.

Levothyroxine, which is a part of the drug, is similar in action to human endogenous thyroid hormones. In the body, levothyroxine is metabolized to lyothyronine, which, when ingested into cells and tissues, is able to regulate the development and growth of cells, and to influence metabolism. In particular, the drug is able to influence oxidative metabolism in the mitochondria and selectively regulate the flow of cations inside and outside the cell. In addition, the effect of levothyroxine depends on its dosage, so, in small doses, it is able to have anabolic effect, in the middle it affects mainly cells and tissues

How Should I Use This Medication?

The whole dose of the drug is taken at a time, preferably in the morning, on an empty stomach 30 minutes before a meal, with a sufficient amount of water. Breast children, the tablet is ground and dissolved in a small amount of water, the resulting suspension is given 30 minutes before the first morning feeding, it is necessary to prepare the suspension immediately before taking.

The dose of the drug is selected individually, taking into account the weight, age, severity and nature of the disease, laboratory indicators characterizing the functional state of the thyroid gland.

Usually the initial dose for adults with hypothyroidism and euthyroid goiter is 25-100 mcg per day, then the dose is gradually increased every 2-3 weeks by 25-50 mcg until a maintenance dose is reached. For children, the initial dose of 12.5-50 mcg per day, the maintenance dose is achieved in the same way as for adults.

In severe form of hypothyroidism or in the case of hypothyroidism, which has existed for a long time, the initial dose is reduced and the dose is increased more slowly.

In malignant tumors of the thyroid gland, after surgery, 150-300 mg per day is prescribed.

In hypothyroidism, caused by the removal of part or all of the thyroid gland, levothyroxine is taken throughout life. To carry out the diagnosis by the method of the suppression scintigram, levothyroxine is prescribed at a dose of 200 mg per day for 14 days, or 3 mg once a week before the repeated test.