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- 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:
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]).
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.
Taking levothyroxine at the same time as calcium carbonate, ferrous sulphate, 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.
FDA Prescribing Information
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.
Multimedia: Slideshows, Images & Quizzes
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Hashimoto's ThyroiditisHashimoto's thyroiditis is the most common cause of hypothyroidism in the US. This conditions is caused by inflammation of the thyroid gland. Symptoms may include:
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- cold intolerance,
- excessive sleepiness,
- dry or coarse hair,
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Hypothyroidism During PregnancyHypothyroidism during pregnancy can be treated with synthetic thyroid hormones to maintain the proper thyroid hormone balance. Hypothyroidism symptoms include fatigue, weight gain, lethargy, and constipation. Treatment of hypothyroidism in pregnant women is important, because inadequate levels of thyroid hormones may affect the fetus, and child during growth and development.
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Pendred SyndromePendred syndrome, a genetic disorder that causes hearing loss. Generally, the hearing loss is affected in early childhood. Pendred syndrome also affects other parts fo the body (for example, the thyroid gland). Treatment is generally cochlear ear implants.
Thyroid Blood TestsThyroid blood tests determine the adequacy of the levels of thyroid hormones in in a patient. The blood tests can determine if the thyroid gland's hormone production is normal, overactive , or underactive. The level of thyroid hormones may help to diagnose hypothyroidism or hyperthyroidism. The test may also point to other diseases of conditions of the thyroid gland.
Thyroid DisordersThere 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.
Thyroid NodulesThyroid 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.
Illustrations of ThyroidThe thyroid is a butterfly-shaped gland located in the front of the neck just below the Adams apple. See a picture of the Thyroid and learn more about the health topic.
Take the Thyroid QuizYour unexplained change in weight could indicate a thyroid condition. Take the Thyroid Quiz to learn about common symptoms and treatments of overactive and underactive thyroid disorders.
thyroid replacement-oralThyroid replacement hormones are prescription drugs prescribed to treat hypothyroidism. Side effects, drug interactions, dosage, and pregnancy safety information should be reviewed prior to taking this medication.
Thyroid ScanThyroid scanning is used to determine how active the thyroid is in manufacturing thyroid hormone. This can determine whether inflammation of the thyroid gland (thyroiditis) is present. It can also detect the presence and degree of overactivity of the gland (hyperthyroidism) or, conversely, it can determine the presence and degree of underactivity of the gland (hypothyroidism).
ThyroiditisThyroiditis is the inflammation of the thyroid gland. The inflamed thyroid gland can release an excess of thyroid hormones into the blood stream, resulting in a temporary hyperthyroid state. Some forms of thyroiditis can be diagnosed based on tenderness and enlargement of the thyroid gland. A thyroid scan sometimes is used in making the diagnosis. Thyroiditis can also be diagnosed with a biopsy of the thyroid gland.