Use this medicine only as directed by your doctor. Do not use more or less of it and do not use it more often or for a longer time than your doctor ordered. To do so may increase the chance of side effects.

This medicine works best when there is a constant amount in the blood. To help keep the amount constant, do not miss any doses. Also, if you are taking more than one dose a day, it is best to take the doses at evenly spaced times day and night. For example, if you are to take 3 doses a day, the doses should be spaced about 8 hours apart. If this interferes with your sleep or other daily activities, or if you need help in planning the best times to take your medicine, check with your health care professional.

Food in your stomach may change the amount of methimazole that is able to enter the bloodstream. To make sure that you always get the same effects, try to take methimazole at the same time in relation to meals every day. That is, always take it with meals or always take it on an empty stomach.

Dosing

The dose of these medicines will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of these medicines. If your dose is different, do not change it unless your doctor tells you to do so.

The number of tablets that you take or the number of suppositories that you use depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are taking antithyroid agents.

For methimazole
• For oral dosage form (tablets):
  • For treatment of hyperthyroidism (overactive thyroid):
    • Adults and teenagers At first, 15 to 60 milligrams (mg) a day for up to six to eight weeks. Later, your doctor may want to lower your dose to 5 to 30 mg a day. This may be taken once a day or it may be divided into two doses a day.
    • Children Dose is based on body weight and must be determined by your doctor. The usual dose is 0.4 mg per kilogram (kg) (0.18 mg per pound) of body weight a day. Later, your doctor may want to lower the dose to 0.2 mg per kg (0.09 mg per pound) of body weight a day. The dose may be taken once a day or it may be divided into two doses a day.
  • For treatment of thyrotoxicosis (a thyroid emergency):
    • Adults and teenagers 15 to 20 mg every four hours.
• For rectal dosage form (suppositories):
  • For treatment of thyrotoxicosis (a thyroid emergency):
    • Adults and teenagers 15 to 20 mg inserted into the rectum every four hours. Your doctor may change your dose as needed.
    • Children The dose is based on body weight and must be determined by your doctor. The usual dose is 0.4 mg per kg (0.18 mg per pound) of body weight inserted into the rectum a day. This may be used as a single dose or it may be divided into two doses a day.

For propylthiouracil
• For oral dosage form (tablets):
  • For treatment of hyperthyroidism (overactive thyroid):
    • Adults and teenagers At first, 300 to 900 milligrams (mg) a day. Some people may need up to 1200 mg a day. This may be taken as a single dose or it may be divided into two to four doses in a day. Later, your doctor may lower your dose to 50 to 600 mg a day.
    • Children 6 to 10 years of age At first, 50 to 150 mg a day. This may be taken as a single dose or it may be divided into two to four doses in a day. Later, your doctor may change your dose as needed.
    • Children 10 years of age and older At first, 50 to 300 mg a day. This may be taken as a single dose or it may be divided into two to four doses in a day. Then, your doctor may change your dose as needed.
  • For treatment of thyrotoxicosis (a thyroid emergency):
    • Adults and teenagers 200 to 400 mg every four hours. Your doctor will lower your dose as needed.
    • Newborn infants Dose is based on body weight and must be determined by your doctor. The usual dose is 10 mg per kilogram (kg) (4.5 mg per pound) of body weight a day. This is usually divided into more than one dose a day.
• For rectal dosage forms (enemas or suppositories):
  • For treatment of thyrotoxicosis (a thyroid emergency):
    • Adults and teenagers 200 to 400 mg inserted into the rectum every four hours. Your doctor may change your dose as needed.
    • Children 6 to 10 years of age 50 to 150 mg inserted into the rectum a day. This dose may be used as a single dose or it may be divided into two to four doses in a day. Your doctor may change your dose as needed.
    • Children 10 years of age and older 50 to 300 mg inserted into the rectum a day. This dose may be used as a single dose or it may be divided into two to four doses in a day. Your doctor may change your dose as needed.
    • Newborn infants Dose is based on body weight and must be determined by your doctor. The usual dose is 10 mg per kg (4.5 mg per pound) of body weight inserted into the rectum. This is usually divided into more than one dose a day. Your doctor may change your dose as needed.

Missed dose

If you miss a dose of this medicine, take it as soon as possible. If it is almost time for your next dose, take both doses together. Then go back to your regular dosing schedule. If you miss more than one dose or if you have any questions about this, check with your doctor.

Storage

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other high-moisture areas. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

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.

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

• 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