Methimazole

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Methimazole

Methimazole is an antithyroid drug similar in action to propylthiouracil.

Indications

Methimazole is used to treat hyperthyroidism, a condition that usually occurs when the thyroid gland produces too much thyroid hormone. It is also taken before thyroid surgery or radioactive iodine therapy. This medication is sometimes prescribed for other uses; ask your healthcare provider or pharmacist for more information.

Form

Methimazole comes as a tablet and may be taken from one to three times a day, with food (check with your healthcare provider or pharmacist for further information). Follow the directions on your prescription label carefully, and ask your healthcare provider or pharmacist to explain any part you do not understand.

Adverse Effects

Contact your healthcare provider IMMEDIATELY if a fever or sore throat develops while taking methimazole; this could indicate the development of agranulocytosis, an uncommon side effect resulting from a drop in the white blood cell count (specifically, neutropenia, which indicates a deficiency of neutrophils). A complete blood count (CBC) with differential needs to be evaluated by your healthcare provider.

General Side Effects

Although side effects from methimazole are not common (~5%), they can occur. Tell your healthcare provider if any of these symptoms are severe or persist:

skin rash
itching
abnormal hair loss
upset stomach
vomiting
loss of taste
abnormal sensations (tingling, prickling, burning, tightness, and pulling)
swelling
joint and muscle pain
drowsiness
dizziness
decreased white blood cells
decreased platelets

If you experience any of the following symptoms, call your healthcare provider immediately:

sore throat
fever
headache
chills
unusual bleeding or bruising
right-sided abdominal pain with decreased appetite
yellowing of the skin or eyes
skin eruptions

Drug Warnings

Before taking Methimazole

Tell your healthcare provider and pharmacist if you are allergic to methimazole, propylthiouracil, lactose, or any other drugs.
Tell your healthcare provider and pharmacist what prescription and nonprescription medications you are taking, especially anticoagulants ('blood thinners') such as warfarin (Coumadin), beta blockers such as propranolol (Inderal), diabetes medications, digoxin (Lanoxin), theophylline (Theobid, Theo-Dur), and vitamins.
Tell your healthcare provider if you have or have ever had any blood disease, such as decreased white blood cells (leukopenia), decreased platelets (thrombocytopenia), or aplastic anemia, or liver disease (hepatitis, jaundice).
Tell your healthcare provider if you are pregnant, plan to become pregnant, or are breast-feeding. An alterntive anti-thyroid drug, propylthiouracil is often substituted during pregnancy or breast-feeding. If you become pregnant while taking methimazole, discuss with your healthcare provider whether you should switch to propylthiouracil with your healthcare provider. Early studies suggested that methimazole may harm the fetus, although more recent studies suggest this may not be the case.
If you are having surgery, including dental surgery, tell the healthcare provider or dentist that you are taking Methimazole.