From the Guidelines
Methimazole dosing should be initiated at the lowest possible dose, with the goal of maintaining FT4 or FTI in the high-normal range, and adjusted every two to four weeks based on thyroid function tests, as recommended by the American College of Obstetricians and Gynecologists 1. When treating hyperthyroidism in pregnancy, methimazole can be used, and the dosage should be tailored to the individual patient's needs.
- The initial dose is not explicitly stated in the provided evidence, but it is generally recommended to start with a low dose and adjust as needed.
- Monitoring of thyroid function tests, such as FT4 or FTI, should be performed every two to four weeks to ensure the dose is adequate and to minimize the risk of side effects 1.
- Potential side effects of methimazole include agranulocytosis, hepatitis, vasculitis, and thrombocytopenia, and patients should be instructed to report any symptoms such as sore throat, fever, or jaundice immediately 1.
- It is essential to note that methimazole can be used safely during breastfeeding, and women treated with this medication can breastfeed without concern 1.
- The dosage may need to be adjusted based on the patient's response to treatment, and the goal is to use the lowest possible dose to maintain euthyroidism 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.
- Initial Dosing:
- Adults: 15 mg (mild hyperthyroidism), 30-40 mg (moderately severe hyperthyroidism), or 60 mg (severe hyperthyroidism) per day, divided into 3 doses at 8-hour intervals.
- Pediatric: 0.4 mg/kg of body weight per day, divided into 3 doses at 8-hour intervals.
- Maintenance Dosing:
- Adults: 5 mg to 15 mg per day.
- Pediatric: approximately 1/2 of the initial dose. The dosing of Methimazole is based on the severity of hyperthyroidism and the patient's age, with adjustments made for maintenance therapy 2.
From the Research
Dosing Methimazole
- The effectiveness of methimazole in a single daily dose for the treatment of hyperthyroidism has been studied in several research papers 3, 4, 5, 6.
- A study published in 1986 found that a single daily dose of 15 mg methimazole was effective in treating hyperthyroidism in most patients, with 93% of patients becoming euthyroid within 12 weeks 3.
- Another study published in 1980 found that all patients treated with a single daily dose of methimazole became euthyroid, with a mean time to achieve euthyroidism of 16.7 weeks 4.
- A prospective randomized trial published in 1988 found that a small single daily dose of 15 mg methimazole was as effective as conventional divided doses in treating Graves' hyperthyroidism, with almost 80% of patients in both groups becoming euthyroid within 8 weeks 5.
- A study published in 1997 found that there was no difference in the clinical and immunological course or in the long-term remission rate of Graves' hyperthyroidism when treatment was initiated with either a small single daily dose (15 mg) or the conventional regimen (10 mg 3 times daily) 6.
- In terms of safety, a study published in 2016 found that methimazole treatment can induce insignificant liver function test (LFT) elevation, and that MMI can be safely administered in hyperthyroid patients with abnormal LFT 7.
Dosage Regimens
- The studies suggest that a single daily dose of 15 mg methimazole is a effective and safe dosage regimen for the treatment of hyperthyroidism 3, 5, 6.
- The conventional divided dose regimen of 10 mg 3 times daily is also effective, but may be associated with more adverse effects 3, 6.
- The optimal dosage regimen may depend on individual patient factors, such as the severity of hyperthyroidism and the presence of underlying liver disease 7.