- What is levothyroxine sodium, and how does it work (mechanism of action)?
- What brand names are available for levothyroxine sodium?
- Is levothyroxine sodium available as a generic drug?
- Do I need a prescription for levothyroxine sodium?
- What are the side effects of levothyroxine sodium?
- What is the dosage for levothyroxine sodium?
- Which drugs or supplements interact with levothyroxine sodium?
- Is levothyroxine sodium safe to take if I'm pregnant or breastfeeding?
- What else should I know about levothyroxine sodium?
What is levothyroxine sodium, and how does it work (mechanism of action)?
Levothyroxine is a synthetic (man-made) version of the principle thyroid hormone, thyroxine (T4) that is made and released by the thyroid gland. Thyroid hormone increases the metabolic rate of cells of all tissues in the body. In the fetus and newborn, thyroid hormone is important for the growth and development of all tissues including bones and the brain. In adults, thyroid hormone helps to maintain brain function, utilization of food, and body temperature, among other effects.
What brand names are available for levothyroxine sodium?
Synthroid, Levoxyl, Levothroid, Unithroid, Tirosint, Levo-T (discontinued brand)
Is levothyroxine sodium available as a generic drug?
GENERIC AVAILABLE: Yes. Generic and branded tablets of levothyroxine may differ:
- in the amount of levothyroxine they contain,
- the absorption of the levothyroxine into the body, and
- the distribution of levothyroxine throughout the body.
This means that ingestion of 1 mg of generic levothyroxine may not have the same effect on the body as 1 mg of another generic or branded levothyroxine. Practically speaking, this means that when changing between levothyroxine manufactured by different pharmaceutical companies, a change in dose may be necessary to maintain the desired effect or to prevent toxicity. When switching between brands or generics, it is important to ensure that both preparations are equivalent or to check blood thyroid levels weekly.
What are the side effects of levothyroxine sodium?
Levothyroxine therapy usually is well-tolerated. If symptoms occur, they often are due to toxic levels of thyroid hormone, and the symptoms are those of hyperthyroidism.
The most commonly reported side effects include:
- chest pain,
- increased heart rate or pulse rate,
- excessive sweating,
- heat intolerance,
- weight loss, or
- Women may experience irregular menstrual cycles.
What is the dosage for levothyroxine sodium?
For adult hypothyroidism, levothyroxine is started at 12.5-125 mcg/day administered orally. Starting doses and dose changes may differ with individual patients based upon age, the presence of cardiovascular disease, the development of tolerance (reduced effectiveness with continued use), side effects to the medication, and blood levels of thyroid hormone. It may take one to three weeks after initiating therapy with levothyroxine or changing the dose before effects are seen. The goal of replacement therapy is to maintain a normal blood thyroxine level.
Which drugs or supplements interact with levothyroxine sodium?
Initiation or discontinuation of therapy with levothyroxine in diabetic patients may create a need for an increase or decrease in the required dose of insulin and/or antidiabetic drug, (for example, glyburide [Micronase]).
Levothyroxine may increase the effect of blood thinners such as warfarin (Coumadin). Therefore, monitoring of blood clotting is necessary, and a decrease in the dose of warfarin may be necessary.
Intravenous administration of epinephrine to patients with coronary artery disease may lead to complications ranging from difficulty in breathing to a heart attack. These complications may occur more frequently among patients also taking levothyroxine. Therefore, careful observation is needed when intravenous epinephrine is given to patients receiving levothyroxine who also have coronary artery disease.
Converting a state of hypothyroidism (under activity) to a normal state (euthyroid state) with levothyroxine may decrease the actions of certain beta-blocking drugs, (for example, metoprolol [Lopressor] or propranolol [Inderal]). It may be necessary, therefore, to change the dose of beta-blocker. For the same reason, the dose of digoxin (Lanoxin), a drug used to manage heart failure or an irregular heart rhythm (for example, atrial fibrillation), also may need to be changed.
Converting hypothyroidism to the euthyroid state with levothyroxine may increase the blood level of theophylline (Slo-Bid), and it may be necessary to change the dose of theophylline.
Taking levothyroxine at the same time as calcium carbonate, ferrous sulfate, cholestyramine (Questran) or colestipol (Colestid) may decrease the effect of levothyroxine and lead to hypothyroidism. This occurs because the levothyroxine binds to these drugs and is not absorbed. Taking the levothyroxine one hour before or four hours after these drugs is necessary to prevent binding.
Is levothyroxine sodium safe to take if I'm pregnant or breastfeeding?
Thyroid hormone therapy in nursing mothers is usually safe but should be supervised by a physician.
What else should I know about levothyroxine sodium?
What preparations of levothyroxine sodium are available?
- Tablets: 0.025, 0.05, 0.075, 0.088, 0.1, 0.112, 0.125, 0.137, 0.15, 0.175, 0.2 and 0.3 mg.
- Capsules: 0.013, 0.025, 0.05, 0.075, 0.088, 0.1, 0.125 and 0.15 mg.
- Powder for intravenous injection: 200 mcg and 500 mcg per vial.
How should I keep levothyroxine sodium stored?
Levothyroxine tablets, capsules, and dry powder should be kept at room temperature, 15 C to 30 C (59 F to 86 F) in a light-resistant, tight container.
Powdered levothyroxine for intravenous injection should be used immediately once mixed with liquid.
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Levothyroxine (Synthroid, Levoxyl, Levothroid, Unithroid, Tirosint, Levo-T) is a synthetic version of the principle thyroid hormone, thyroxine (T4), which is made and released by the thyroid gland. Thyroid hormone increases the metabolic rate of cells of all tissues in the body. It is prescribed to treat hypothyroidism and to suppress thyroid hormone release in the management of cancerous thyroid nodules and growth of goiters. It is important to be aware of drug interactions, as well as common side effects on the user.
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Related Disease Conditions
Hypothyroidism is any state in which thyroid hormone production is below normal. Normally, the rate of thyroid hormone production is controlled by the brain by the pituitary gland. Hypothyroidism is a very common condition and the symptoms of hypothyroidism are often subtle but may include constipation, memory loss, hair loss, and depression. There are a variety of causes of hypothyroidism, and treatment depends on the cause.
There are several types of thyroid disorders including hypothyroidism, hyperthyroidism, goiters, thyroid nodules, and thyroid cancer. Symptoms vary by condition. Diagnosis is made with blood tests, scans, ultrasound, or biopsy. Treatments depend on the disorder and can include medication or surgery.
Hashimoto's thyroiditis or chronic lymphocytic thyroiditis is an autoimmune disorder causing inflammation of the thyroid gland. Hashimoto's thyroiditis is a type of hypothyroidism and is the most common cause of hypothyroidism in the US. Symptoms of Hashimoto's thyroiditis may include dry skin, fatigue, weight gain, feeling cold, excessive sleepiness, dry skin, dry coarse hair, difficulty swallowing, a lump in the front of the throat, muscle cramps, mood changes, vague aches and pains, problems concentrating, leg swelling, constipation, and depression. There is no cure for Hashimoto’s thyroiditis. Diet changes, natural supplements, vitamins, or other natural products will not treat Hashimoto’s thyroiditis. Treatment for the autoimmune disorder is with thyroid hormone replacement therapy, which will be necessary for the rest of the person’s life.
Hypothyroidism During Pregnancy
Hypothyroidism during pregnancy can be treated with synthetic thyroid hormones to maintain the proper thyroid hormone balance. Hypothyroidism symptoms and signs include fatigue, weight gain, lethargy, and constipation. Check out the center below for more medical references on pregnancy and hypothyroidism, including multimedia (slideshows, images, and quizzes), related disease conditions, treatment and diagnosis, medications, and prevention or wellness.
Thyroid nodules are the most common endocrine problem in the United States. The term thyroid nodule refers to any abnormal growth that forms a lump in the thyroid gland. The vast majority of thyroid nodules are benign.
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