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What is the most important information I should know about methimazole?

Do not take methimazole if you are breast-feeding a baby.

Do not use this medication without telling your doctor if you are pregnant. It could cause harm to the unborn baby. Use an effective form of birth control, and tell your doctor if you become pregnant during treatment.

Methimazole can increase your risk of bleeding. If you need to have surgery, tell the surgeon ahead of time that you are using this medication.

Methimazole can lower the blood cells that help your body fight infections. This can make it easier for you to get sick from being around others who are ill. To be sure your blood cells do not get too low, your blood will need to be tested on a regular basis. Do not miss any scheduled visits to your doctor.

Do not receive a "live” vaccine while you are being treated with methimazole, and avoid coming into contact with anyone who has recently received a live vaccine. There is a chance that the virus could be passed on to you.

Keep using this medication even if you feel fine or have no symptoms of hyperthyroidism. You may need to keep taking methimazole long term to control your condition. Stopping the medication could cause your symptoms to return.

Warning

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

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What is methimazole?

Methimazole prevents the thyroid gland from producing too much thyroid hormone.

Methimazole is used to treat hyperthyroidism (overactive thyroid). It is also used before thyroid surgery or radioactive iodine treatment.

Methimazole may also be used for purposes other than those listed in this medication guide.


Precautions

Do not use this medication if you are allergic to methimazole.

Before taking methimazole, tell your doctor if you are allergic to any drugs, or if you have:

  • liver disease;
  • a blood cell disorder; or
  • a weak immune system.

If you have any of these conditions, you may not be able to use methimazole, or you may need dosage adjustments or special tests during treatment.

FDA pregnancy category D. This medication can cause harm to an unborn baby. Do not use methimazole without your doctor’s consent if you are pregnant. Tell your doctor if you become pregnant during treatment. Use an effective form of birth control while you are using this medication.

Methimazole can pass into breast milk and may harm a nursing baby. Do not use methimazole if you are breast-feeding a baby.

Avoid being near people who have colds, the flu, or other contagious illnesses. Contact your doctor at once if you develop signs of infection.

Do not receive a "live” vaccine while you are being treated with methimazole, and avoid coming into contact with anyone who has recently received a live vaccine. There is a chance that the virus could be passed on to you.

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Instructions

Seek emergency medical attention if you think you have used too much of this medicine.

Symptoms of a methimazole overdose may include nausea, vomiting, upset stomach, headache, joint pain, fever, itching, swelling, or pale skin and easy bruising or bleeding.

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at your next regularly scheduled time. Do not take extra medicine to make up the missed dose.

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Side-effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop taking methimazole and call your doctor at once if you have any of these serious side effects:

  • fever, chills, sore throat, body aches, flu symptoms;
  • easy bruising or bleeding, unusual weakness;
  • blood in your urine or stools;
  • severe blistering, peeling, and red skin rash; or
  • nausea, stomach pain, low fever, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Keep taking methimazole and talk with your doctor if you have any of these less serious side effects:

  • headache, drowsiness, dizziness;
  • mild nausea, vomiting, or stomach upset;
  • itching, minor skin rash;
  • muscle, joint, or nerve pain;
  • swelling; or
  • hair loss.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

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Interactions

Before taking methimazole, tell your doctor if you are using any of the following drugs:

  • theophylline (Theo-Dur, Elixophyllin, Uniphyl, and others);
  • a blood thinner such as warfarin (Coumadin);
  • digoxin (digitalis, Lanoxin); or
  • a beta-blocker such as acebutolol (Sectral), atenolol (Tenormin), betaxolol (Kerlone), bisoprolol (Zebeta), carteolol (Cartrol), carvedilol (Coreg), esmolol (Brevibloc), labetalol (Normodyne, Trandate), metoprolol (Lopressor, Toprol), nadolol (Corgard), penbutolol (Levatol), pindolol (Visken), propranolol (Inderal, InnoPran), sotalol (Betapace), or timolol (Blocadren).

If you are using any of these drugs, you may not be able to use methimazole, or you may need dosage adjustments or special tests during treatment.

There may be other drugs not listed that can affect methimazole. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

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Disclaimer

Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.

Copyright 1996-2004 Cerner Multum, Inc. Version 2.05. Revision date 8/23/04

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