- Hyperthyroidism Slideshow Pictures
- Take the Thyroid Disorder Quiz
- Thyroid Symptoms and Solutions Slideshow Pictures
- What is methimazole, and how does it work (mechanism of action)?
- What brand names are available for methimazole?
- Is methimazole available as a generic drug?
- Do I need a prescription for methimazole?
- What are the side effects of methimazole?
- What is the dosage for methimazole?
- Which drugs or supplements interact with methimazole?
- Is methimazole safe to take if I'm pregnant or breastfeeding?
- What else should I know about methimazole?
What is methimazole, and how does it work (mechanism of action)?
Methimazole is used to treat an overactive thyroid gland (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 or supplements interact with methimazole?
: Warfarin (Coumadin) 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).
Is methimazole safe to take if I'm pregnant or 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).
PRESCRIBED FOR: Methimazole is used for treating 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.
Multimedia: Slideshows, Images & Quizzes
Thyroid Quiz: Test Your Medical IQ
Your unexplained change in weight could indicate a thyroid condition. Take the Thyroid Quiz to learn about common symptoms and...
Picture of Graves Disease
Generalized diffuse overactivity ("toxicity") of the entire thyroid gland which becomes enlarged into a goiter. See a picture of...
Hyperthyroidism Symptoms and Treatment
What is hyperthyroidism? Hyperthyroidism occurs when an overactive thyroid gland produces an excessive amount of thyroid...
Related Disease Conditions
Hyperthyroidism (Symptoms, Causes, Treatment Medication, Diet)
Hyperthyroidism is an excess of thyroid hormone due to an overactive thyroid gland. Symptoms can include increased heart rate,...
Thyroiditis is the inflammation of the thyroid gland. The inflamed thyroid gland can release an excess of thyroid hormones into...
There are several types of thyroid disorders including hypothyroidism, hyperthyroidism, goiters, thyroid nodules, and thyroid...
Graves' Disease (Symptoms, Causes, Diet, Treatment Options)
Graves' disease is an autoimmune disease that affects the thyroid. Some of the symptoms of Graves' disease include hand tremors,...
Treatment & Diagnosis
- Thyroid FAQs
- Drugs: Buying Prescription Drugs Online Safely
- Drugs: The Most Common Medication Errors
- How To Reduce Your Medication Costs
- Pharmacy Visit, How To Get The Most Out of Your Visit
- Indications for Drugs: Approved vs. Non-approved
- Medication Disposal
- Dangers of Mixing Medications
- Thyroid Storm
- Generic Drugs, Are They as Good as Brand-Names?
Medications & Supplements
Prevention & Wellness
Health Solutions From Our Sponsors
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
FDA Prescribing Information