Methimazole Dosage

Medically reviewed by Drugs.com. Last updated on Mar 20, 2023.

Applies to the following strengths: 5 mg; 10 mg; 15 mg; 20 mg

Usual Adult Dose for Hyperthyroidism

Initial dose:
Mild hyperthyroidism: 15 mg orally per day
Moderately severe hyperthyroidism: 30 to 40 mg orally per day
Severe hyperthyroidism: 60 mg orally per day

Maintenance dose:
5 to 15 mg orally per day

Comments: Daily doses are usually given in 3 divided doses at approximately 8 hour intervals

Uses:

For the treatment of Graves' disease with hyperthyroidism or toxic multinodular goiter in whom surgery or radioactive iodine therapy is not an appropriate treatment option.
To ameliorate symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy.

Usual Pediatric Dose for Hyperthyroidism

Initial dose: 0.4 mg/kg orally per day

Maintenance dose: 0.2 mg/kg orally per day (approximately half the initial dose)

Comments: Daily doses are usually given in 3 divided doses at approximately 8 hour intervals

Renal Dose Adjustments

Data not available

Liver Dose Adjustments

Data not available

Dose Adjustments

An elevated TSH, during periodic monitoring of thyroid function, should lead to a decrease in the dosage of methimazole.

Precautions

CONTRAINDICATIONS:

Hypersensitivity to the active substance or any product excipients

Consult WARNINGS section for additional precautions.

Dialysis

Data not available

Other Comments

Administration advice:

Take orally in equally divided doses at approximately 8-hour intervals

General:

Patients treated with this drug should be under close surveillance due to the potential for serious adverse effects.
Avoid use during the first trimester of pregnancy due to reports of fetal abnormalities; after the first trimester it may be preferable to switch to methimazole due to hepatotoxicity of propylthiouracil.

Monitoring:

Routine monitoring of TSH and free T4 levels is necessary to avoid under or over treatment
Consider monitoring prothrombin time if there are concerns of bleeding; prothrombin time should be monitored before surgical procedures
Obtain complete blood counts if there are signs and symptoms of agranulocytosis
Perform liver function testing if there are any symptoms of hepatic dysfunction

Patient advice:

Patients should understand the importance of contacting their healthcare provider promptly if they experience any signs or symptoms of liver dysfunction, low blood counts, bleeding, or vasculitis.
Women should be instructed to speak to their healthcare provider if they are pregnant or plan to become pregnant.