What is the recommended treatment and dosage of Methimazole (generic name) for hyperthyroidism?

From the Guidelines

Methimazole is recommended at an initial dose of 10-30 mg daily for hyperthyroidism, with the goal of maintaining FT4 or FTI in the high-normal range using the lowest possible thioamide dosage. The specific dosage depends on the severity of the condition, with mild cases potentially starting at 5-10 mg daily and moderate to severe cases requiring 20-30 mg daily, often divided into 2-3 doses 1. According to the most recent guidelines, methimazole is preferred in the second and third trimesters of pregnancy, while propylthiouracil is preferred in the first trimester due to possible teratogenicity with methimazole 1.

Key Considerations

• The dose of methimazole should be gradually reduced to a maintenance level of 5-15 mg daily once thyroid levels normalize, usually within 4-8 weeks 1.
• Treatment typically continues for 12-18 months, after which some patients may achieve remission.
• Common side effects include rash, itching, and rarely, agranulocytosis (severe decrease in white blood cells) 1.
• Regular blood tests are essential to monitor thyroid function and medication effects, typically every 4-6 weeks initially, then every 2-3 months once stabilized.
• Patients should take the medication at the same time each day, with or without food, and report symptoms like fever, sore throat, or unusual bleeding immediately as these could indicate serious side effects.

Monitoring and Adjustments

• Measuring the FT4 or FTI every two to four weeks can be helpful in adjusting the dosage of methimazole 1.
• A beta blocker (e.g., propranolol) can be used to reduce symptoms until thioamide therapy reduces thyroid hormone levels 1.
• If symptoms of agranulocytosis develop, such as sore throat and fever, a complete blood cell count should be obtained, and the thioamide should be discontinued 1.

From the FDA Drug Label

DOSAGE AND ADMINISTRATION Methimazole tablets, USP are administered orally. The total daily dosage is usually given in 3 divided doses at approximately 8-hour intervals. Adult The initial daily dosage is 15 mg for mild hyperthyroidism, 30 mg to 40 mg for moderately severe hyperthyroidism and 60 mg for severe hyperthyroidism, divided into 3 doses at 8-hour intervals. The maintenance dosage is 5 mg to 15 mg daily. Pediatric Initially, the daily dosage is 0.4 mg/kg of body weight divided into 3 doses and given at 8-hour intervals. The maintenance dosage is approximately 1/2 of the initial dose.

The recommended treatment and dosage of Methimazole for hyperthyroidism are as follows:

• Adults:
  • Initial daily dosage:
    • 15 mg for mild hyperthyroidism
    • 30 mg to 40 mg for moderately severe hyperthyroidism
    • 60 mg for severe hyperthyroidism
  • Maintenance dosage: 5 mg to 15 mg daily
• Pediatric:
  • Initial daily dosage: 0.4 mg/kg of body weight
  • Maintenance dosage: approximately 1/2 of the initial dose 2

From the Research

Recommended Treatment and Dosage of Methimazole for Hyperthyroidism

The recommended treatment and dosage of Methimazole for hyperthyroidism vary depending on the severity of the condition and the patient's response to the medication.

• The initial dose of Methimazole for severe Graves' disease hyperthyroidism is usually 30 mg/day, but this dose is associated with more frequent adverse effects compared to a lower dose of 15 mg/day 3.
• A study compared the efficacy and adverse effects of Methimazole 15 mg + inorganic iodine 38 mg/day (M15+I) and Methimazole 30 mg/day (M30) as initial therapy for Graves' disease patients with moderate to severe hyperthyroidism, and found that the M15+I group had a higher proportion of patients achieving euthyroidism within 30 and 60 days, with fewer adverse effects requiring discontinuation of Methimazole 3.
• Another study found that low-dose Methimazole (1.25-2.5 mg daily) was effective in controlling hyperthyroidism in a patient with Graves' disease, even after multiple recurrences, without any adverse events during three decades of treatment 4.
• The response to Methimazole in Graves' disease is influenced by factors such as the daily dose, pretreatment T3 levels, and goitre size, with higher doses and larger goitres associated with a delayed response 5.
• A single daily dose of 15 mg Methimazole was found to be effective in treating hyperthyroidism due to Graves' disease, with a lower frequency of adverse effects compared to a higher dose of 30 mg 6.
• A comparison of single daily doses of Methimazole and propylthiouracil in the treatment of Graves' hyperthyroidism found that Methimazole was more effective in inducing euthyroidism and reducing serum TRAb levels 7.

Dosage Considerations

• The dosage of Methimazole should be individualized based on the patient's response to the medication and the severity of their hyperthyroidism.
• A lower dose of Methimazole (15 mg/day) may be associated with fewer adverse effects, but may not be as effective in inducing euthyroidism as a higher dose (30 mg/day) 3, 6.
• The use of inorganic iodine in combination with Methimazole may enhance the therapeutic effect and reduce the frequency of adverse effects 3.