- Side Effects
- Drug Interactions
- Pregnancy & Breastfeeding
- What Else to Know
Generic Name: methimazole
Brand Names: Tapazole, Northyx (discontinued)
Drug Class: Antithyroid Agents
What is methimazole, and what is it used for?
Methimazole is used to treat an overactive thyroid gland (hyperthyroidism). It also is used for decreasing symptoms of hyperthyroidism in preparation for surgical removal of the thyroid gland or before inactivating the thyroid gland with radioactive iodine. Long-term use of methimazole may lead to a remission of the hyperthyroidism.
Grave's disease is the most common cause of hyperthyroidism. Grave's disease is an autoimmune disease resulting from antibodies that attach to receptors on thyroid hormone-producing cells in the thyroid gland and trigger overproduction of thyroid hormone. An enzyme (peroxidase) produces thyroid hormones, i.e., thyroxine (T4) and triiodothyronine (T3), by combining iodine with a protein called thyroglobulin. Methimazole prevents iodine and peroxidase from their normal interactions with thyroglobulin to form T4 and T3. This action decreases thyroid hormone production. Methimazole also interferes with the conversion of T4 to T3. Since T3 is more potent than T4, this also reduces the activity of thyroid hormones. The FDA approved methimazole in March 1999.
What are the side effects of methimazole?
Methimazole is generally well-tolerated with side effects occurring in 3 out of every 100 patients. The most common side effects are related to the skin and include:
Other common side effects are:
Less common but more serious side effects include a decrease in white blood cells (agranulocytosis) and blood platelets (thrombocytopenia). Symptoms and signs of agranulocytosis include infections of the throat, the gastrointestinal tract, and skin with an overall feeling of illness and fever. Since platelets are important for the clotting of blood, thrombocytopenia may lead to problems with excessive bleeding. Hepatitis and death of liver cells (hepatic necrosis) have rarely been associated with methimazole.
What is the dosage for methimazole?
The initial adult dose of methimazole is:
- 15 mg/day for mild hyperthyroidism
- 30-40 mg/day for moderately severe hyperthyroidism
- 60 mg/day for severe hyperthyroidism
The daily dose is divided into three doses administered every 8 hours.
The maintenance dose is 5-15 mg/day.
The usual initial children's dose is 0.4 mg/kg given in 3 divided doses administered 8 hours apart, and the maintenance dose is half the initial dose.
Which drugs interact with methimazole?
Warfarin works by reducing the activity of vitamin K and therefore the formation of vitamin K dependent clotting factors. Methimazole may increase the activity of warfarin by further reducing the activity of vitamin K in the body.
Hyperthyroidism increases elimination of beta blockers. Correcting hyperthyroidism will cause less elimination of beta blockers. Therefore, the dose of beta blockers may require reduction when hyperthyroidism is corrected. A similar reaction may also occur with digoxin (Lanoxin) and theophylline (Respbid, Slo-Bid, Theo-24, Theolair).
Pregnancy and breastfeeding
Methimazole is excreted in breast milk and may potentially cause harm to the infant.
What else should I know about methimazole?
What preparations of methimazole are available?
Tablet: 5, 10 mg
How should I keep methimazole stored?
Methimazole should be stored at room temperature, 15 C and 30 C (59 F and 86 F).
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Methimazole (Tapazole) is a medication used to treat hyperthyroidism. Grave's disease is the most common cause of hyperthyroidism. Review side effects, drug interactions, dosage, and pregnancy safety information prior to taking methimazole.
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Related Disease Conditions
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.
Hyperthyroidism is an excess of thyroid hormone due to an overactive thyroid gland. Symptoms can include increased heart rate, weight loss, heart palpitations, frequent bowel movements, depression, fatigue, fine or brittle hair, sleep problems, thinning skin, and irregular vaginal bleeding. Graves' disease is the most common cause of hyperthyroidism. Many other health problems or taking excess thyroid hormone medication can cause an overactive thyroid gland. Treatment for the condition is with medication, radioactive iodine, thyroid surgery (rarely), or reducing the dose of thyroid hormone. No diet has been shown to treat hyperthyroidism or its symptoms and signs.
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What Can You Not Eat With Graves’ Disease
Doctors may ask people with Graves’ disease to avoid certain foods because of the following reasons: These people may have issues with foods that contain iodine. Caffeine and foods with a high caffeine content may aggravate the symptoms of hyperthyroidism. Food allergens (if any) may also cause symptoms similar to those of Graves’ disease (weight loss and diarrhea).
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.
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.
How Does Graves Disease Affect the Body?
Graves’ disease is an autoimmune disease that affects the thyroid gland. In this disease, there is an overproduction of thyroid hormones. Thyroid hormones control the body’s metabolism, so they affect almost all the organs of the body.
What Can Trigger Graves’ Disease?
Researchers believe that Graves’ disease results from a combination of genetics and outside triggers, such as bacteria or viruses.
Does Graves’ Ophthalmopathy Go Away?
Graves’ ophthalmopathy may not go away on its own; however, its symptoms can be effectively managed with adequate treatment.
What Is the Main Cause of Graves' Disease?
While the exact cause of Graves’ disease is unknown, certain factors may put you at an increased risk of developing the autoimmune disease. Learn those factors below.
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What is Graves' disease, and how does it affect your eyes? Learn the signs of thyroid eye disease, what causes it, and how it is treated.
Is Graves’ Disease the Same as Thyrotoxicosis?
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