Methimazole

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Generic Name: Methimazole Brand Name(s): Generics only. No brands available.

Uses

What is methimazole used for?

Methimazole is commonly used for treating an overactive thyroid gland and treating or preparing the overactive thyroid gland for surgery. It may also be used when your doctor has advised against the removal of the thyroid. It may also be for other conditions as determined by your doctor.

Methimazole is an antithyroid agent. It works by inhibiting the production of thyroid hormone. Thyroid hormones are produced and released by the thyroid gland and regulate the body’s metabolism.

How should I take methimazole?

Use methimazole as directed by your doctor. Check the label on the medicine for exact dosing instructions.

Take methimazole by mouth with or without food. If stomach upset occurs, take with food to reduce stomach irritation.

Take methimazole on a regular schedule around the clock, unless your doctor tells you otherwise.

How do I store methimazole?

Methimazole is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store methimazole in the bathroom or the freezer. There may be different brands of methimazole that may have different storage needs. It is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush methimazole down the toilet or pour them into a drain unless instructed to do so. It is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

Precautions & warnings

What should I know before using methimazole?

Before using this drug, tell your doctor if:

  • You are pregnant or breastfeeding. This is because, while you are expecting or feeding a baby, you should only take medicines on the recommendation of a doctor.
  • You are taking any other medicines. This includes any medicines you are taking which are available to buy without a prescription, such as herbal and complementary medicines.
  • You have allergy with any of active or inactive ingredients of methimazole or other medications.
  • You have any other illnesses, disorders, or medical conditions.
  • You have allergies to medicines, foods, or other substances.
  • You have bone marrow or liver problems.
  • You have exfoliative dermatitis (widespread redness and scaling of the skin).

Methimazole may cause drowsiness, dizziness, or lightheadedness. These effects may be worse if you take it with alcohol or certain medicines. Use methimazole with caution. Do not drive or perform other possibly unsafe tasks until you know how you react to it.

Lab tests, including thyroid and liver function tests, complete blood cell counts, and blood clotting tests (e.g., PT, INR), may be performed while you use methimazole. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.

Is it safe during pregnancy or breastfeeding?

There are no adequate studies in women for determining risk when using methimazole during pregnancy or while breastfeeding. Please always consult with your doctor to weigh the potential benefits and risks before taking methimazole. Methimazole is pregnancy risk category D, according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk
  • B=No risk in some studies
  • C=There may be some risk
  • D=Positive evidence of risk
  • X=Contraindicated
  • N=Unknown

Side effects

What side effects can occur from methimazole?

All medicines may cause side effects, but many people have no, or minor, side effects. Check with your doctor if any of these most common side effects persist or become bothersome:

  • Change in taste
  • Dizziness
  • Drowsiness
  • Headache
  • Joint pain
  • Lightheadedness
  • Muscle pain
  • Nausea
  • Numbness and tingling
  • Stomach upset
  • Vomiting

Seek medical attention right away if any of these severe side effects occur:

  • Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue)
  • Changes in appetite
  • Dark urine
  • Fainting
  • Fast or irregular heartbeat
  • Fever, chills, or persistent sore throat
  • Severe or persistent headache, nausea, or vomiting
  • Stomach pain
  • Tremor
  • Unusual bruising or bleeding
  • Unusual hair loss
  • Unusual tiredness or weakness
  • Vision changes
  • Yellowing of the skin or eyes

Not everyone experiences these side effects. There may be some side effects not listed above. If you have any concerns about a side-effect, please consult your doctor or pharmacist.

Interactions

What drugs may interact with methimazole?

Methimazole may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist. For your safety, do not start, stop, or change the dosage of any drugs without your doctor’s approval.

Does food or alcohol interact with methimazole?

Methimazole may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with methimazole?

Methimazole may interact with your health condition. This interaction may worsen your health condition or alter the way the drug works. It is important to always let your doctor and pharmacist know all the health conditions you currently have.

Dosage

The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using this methimazole.

What is the dose of methimazole for an adult?

Usual Adult Dose for Hyperthyroidism

Initial:

Mild hyperthyroidism: 5 mg orally every 8 hours.

Moderately severe hyperthyroidism: 10 mg orally every 8 hours (up to 40 mg per day).

Severe hyperthyroidism: 20 mg orally every 8 hours.

Maintenance: 5 to 15 mg orally daily.

What is the dose of methimazole for a child?

Usual Pediatric Dose for Hyperthyroidism

Greater than or equal to 1 year:

Initial dose: 0.4 mg/kg/day orally in 3 equally divided doses 8 hours apart.

Maintenance dose: 0.2 mg/kg/day orally in 3 equally divided doses 8 hours apart.

Maximum dose: 30 mg/day.

How is methimazole available?

Methimazole is available in the following dosage forms and strengths:

  • Tablet

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room.

What should I do if I miss a dose?

If you miss a dose of methimazole, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Review Date: August 15, 2017 | Last Modified: August 25, 2017

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