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- What are thyroid replacement hormones and how do they work?
- What are some examples of thyroid replacement hormones?
- What are the uses for thyroid replacement hormones?
- Are there any differences among the different types of thyroid replacement hormones?
- What are the side effects of thyroid replacement hormones?
- Which drugs or supplements interact with thyroid replacement hormones?
What are thyroid replacement hormones and how do they work?
Thyroid replacement hormones are medications used to treat hypothyroidism, a condition in which the production of thyroid hormone in the body is abnormally low. Thyroid hormones increase cellular metabolism (activity of cells) that is responsible for growth, development of tissues, maintenance of brain function, body temperature regulation and several other cellular processes. Low levels of thyroid hormones in the body can result in many problems given the numerous activities that they mediate. The thyroid gland, a gland found in the lower neck is responsible for the production of thyroid hormones. It produces two main hormones, thyroxine (T4) and triiodothyronine (T3). The hormone responsible for most of the biological effects in the body is T3. When T4 is released into the blood by the thyroid gland, most of it is converted to T3 which is responsible for the cellular metabolic processes. Commercially available thyroid hormones are either natural or synthetic (man-made). Desiccated thyroid or thyroid extract (Armor Thyroid, Nature-Throid), a natural thyroid hormone is derived from beef or pork. Levothyroxine sodium (for example, Synthroid, Levoxyl and Levothroid), is the synthetic version of thyroxine (T4), liothyronine sodium (Cytomel, Triostat), is the synthetic version of tT3 and liotrix (Thyrolar) is a synthetic thyroid hormone containing a mixture of T4and T3.
What are some examples of thyroid replacement hormones?
The following is a list of the thyroid replacement hormones that are available in the United States:
What are the uses for thyroid replacement hormones?
Thyroid replacement hormones are used to treat hypothyroidism (low production of thyroid hormone) and myxedema, a condition that is caused by prolonged hypothyroidism. Thyroid replacement hormones prevent thyroid hormone release from cancerous thyroid nodules and are used therefore to treat thyroid cancers. They also are used to manage thyrotoxicosis, a condition in which there are high levels of thyroid hormones resulting from over-active thyroid glands and too much thyroid hormone. Thyrotoxicosis may progress to hypothyroidism or cause the growth of goiters necessitating the use of thyroid replacement hormones.
Are there any differences among the different types of thyroid replacement hormones?
There is conflicting evidence regarding which hormone replacement therapy should be preferred. The American Association of Clinical Endocrinologists recommends that clinical hypothyroidism is best treated with synthetic T4 levothyroxine (for example levothyroxine and sodium [Synthroid, Levoxyl and Levothroid]). There is variability between the absorption and distribution of generic T4 compared to brand name preparations. Hence it is recommended that patients remain with specific brand names during treatment. There is also variability between generic formulations and brand names of pure T3 (liothyronine [Cytomel, Triostat]), combined T4/T3 formulations (liotrix [Thyrolar]) and thyroid extracts from animal sources (Armour Thyroid, Nature-Throid etc.). Thyroid extracts from animal sources are no longer available in the United States. Emerging information shows that combination of T4/T3 therapy may have some advantages over T4 in cognitive performance and mood but studies are not conclusive.
What are the side effects of thyroid replacement hormones?
Thyroid replacement hormones usually are well tolerated. Symptoms that occur during treatment are often due to toxic, elevated levels of thyroid hormones and resulting symptoms from hyperthyroidism. Symptoms may include chest pain, increased heart rate or pulse rate, excessive sweating, heat intolerance, nervousness, headache, insomnia, diarrhea, vomiting, weight loss, and fever. Some women may experience irregular menstrual cycles.
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Which drugs or supplements interact with thyroid replacement hormones?
Thyroid replacement hormones should be used cautiously in people with diabetes since starting or discontinuing therapy may lead to a loss of control of the blood sugar requiring adjustments in doses of insulin or oral antidiabetic drugs (for example, glyburide [Micronase]). The effects of blood thinners such as warfarin (Coumadin) may be increased by thyroid replacement hormones warranting a decrease in the dose of warfarin in addition to monitoring of blood clotting.
Intravenous epinephrine administration in patients with coronary artery disease who are taking thyroid replacement hormones may increase the risk of complications such as difficulty in breathing and possibly heart attacks. The effectiveness of some beta blockers [for example, metoprolol (Lopressor) orpropranolol (Inderal)] may be reduced when a patient is converted from a state of hypothyroidism (under activity) to a normal state (euthyroid state). It also may be necessary to modify the dose of digoxin (Lanoxin) and theophylline (Slo-Bid) when a patient is converted from hypothyroidism (under activity) to a normal state (euthyroid state). There is increased elimination of theophylline in a euthyroid state compared to a state of hypothyroidism.
The effectiveness of thyroid replacement hormones may be decreased when given with drugs such as calcium carbonate, ferrous sulphate, cholestyramine (Questran) and colestipol (Colestid) that binds thyroid replacement hormones and prevent their absorption. This interaction may be reduced by separating the administration of these drugs from thyroid replacement hormones by four hours.
Thyroid 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.
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.
Thyroiditis 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.
Hashimoto's Thyroiditis (Symptoms, Diet, Treatments, Pregnancy)
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.
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.
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