Antithyroid Agents (Systemic)

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 used in children and, in effective doses, has not been shown to cause different side effects or problems in children than it does in adults.

Adolescents - This medicine has been used in teenagers and, in effective doses, has not been shown to cause different side effects or problems in teenagers than it does in adults.

Older adults - Elderly people may have an increased chance of certain side effects during treatment. Your doctor may need to take special precautions while you are taking this medicine.

Other medicines - Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking antithyroid agents, it is especially important that your health care professional know if you are taking any of the following:

• Amiodarone or
• Iodinated glycerol or
• Potassium iodide (e.g., Pima) - The use of these medicines may change the effect of antithyroid agents

• Anticoagulants (blood thinners) - The use of antithyroid agents may affect the way anticoagulants work in your body

• Beta-adrenergic blocking agents (e.g., Inderal, Metoprolol, Sotalol) - The use of antithyroid agents may change the amount of beta-blockers you need to take.
• Digitalis glycosides - The use of antithyroid agents may affect the amount of digitalis glycosides in the bloodstream

Other medical problems - The presence of other medical problems may affect the use of antithyroid agents. Make sure you tell your doctor if you have any other medical problems, especially:

• Liver disease - The body may not get this medicine out of the bloodstream at the usual rate, which may increase the chance of side effects