Antithyroid agents (Systemic).

Some commonly used brand names are:

In the U.S. --

 
   Tapazole (Methimazole (meth-IM-a-zole)) 

In Canada --

 
   Propyl-Thyracil (Propylthiouracil (proe-pill-thye-oh-YOOR-a-sill) 
      (Generic name product may also be available in the U.S.)) 
   Tapazole (Methimazole (meth-IM-a-zole)) 

Another commonly used name for methimazole is thiamazole.

Description Methimazole and propylthiouracil are used to treat conditions in which the thyroid gland produces too much thyroid hormone.

These medicines work by making it harder for the body to use iodine to make thyroid hormone. They do not block the effects of thyroid hormone that was made by the body before their use was begun.

Methimazole and propylthiouracil are available only with your doctor's prescription, in the following dosage forms:

 
   Oral 
      Methimazole 
         o Tablets (U.S. and Canada) 
      Propylthiouracil 
         o Tablets (U.S. and Canada) 

Before Using This Medicine In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For antithyroid agents, the following should be considered:

Allergies -- Tell your doctor if you have ever had any unusual or allergic reaction to methimazole or propylthiouracil. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy -- Use of too large a dose during pregnancy may cause problems in the fetus. However, use of the proper dose, with careful monitoring by the doctor, is not likely to cause problems.

Breast-feeding -- These medicines pass into breast milk. (Methimazole passes into breast milk more freely and in higher amounts than propylthiouracil.) However, your doctor may allow you to continue to breast-feed, if your dose is low and the infant gets frequent check-ups. If you are taking a large dose, it may be necessary for you to stop breast-feeding during treatment.

Children -- This medicine has been …