Initial Treatment and Titration of Methimazole for Hyperthyroidism
For patients with hyperthyroidism, methimazole should be initiated at 15 mg daily for mild disease, 30 mg daily for moderate disease, and 60 mg daily for severe disease, with subsequent titration to a maintenance dose of 5-15 mg daily based on thyroid function tests. 1
Initial Dosing Strategy
- For mild hyperthyroidism: Start with 15 mg of methimazole daily 1
- For moderate hyperthyroidism: Start with 30-40 mg of methimazole daily 1
- For severe hyperthyroidism: Start with 60 mg of methimazole daily 1
- The initial daily dose is typically divided into 3 doses given at 8-hour intervals, though single daily dosing may be effective in many cases 1, 2
Monitoring and Titration
- Measure free T4 and TSH levels every 2-4 weeks during initial treatment to assess response 3
- For immune checkpoint inhibitor-related thyrotoxicosis, monitor thyroid function every 2-3 weeks after diagnosis to catch potential transition to hypothyroidism 3
- The goal is to maintain free T4 in the high-normal range using the lowest possible thioamide dosage 3
- Once euthyroidism is achieved, typically within 4-12 weeks, transition to a maintenance dose 2, 4
Maintenance Dosing
- Maintenance dose typically ranges from 5-15 mg daily 1
- For pediatric patients, maintenance dose is approximately half of the initial dose 1
- Once stable, thyroid function tests can be performed less frequently (every 3-6 months) 3
Administration Considerations
- Single daily dosing of 15 mg methimazole has been shown to be effective in most patients with Graves' disease and causes fewer adverse effects than higher doses 2
- For persistent thyrotoxicosis (>6 weeks), consider endocrinology consultation for additional workup and possible adjustment of medical therapy 3
Special Populations
Pregnant Women
- Methimazole can be used in pregnant women with the goal of maintaining free T4 in the high-normal range 3
- Monitor free T4 or free T4 index every 2-4 weeks during pregnancy 3
- Women treated with methimazole can breastfeed safely 3
Severe Cases
- For severe symptoms (Grade 3-4), consider hospitalization 3
- Beta-blockers (e.g., atenolol or propranolol) can be used for symptomatic relief until methimazole reduces thyroid hormone levels 3
- Endocrine consultation is recommended for all severe cases 3
Long-Term Management
- Standard duration of therapy is typically 12-18 months 5, 6
- Long-term continuation of low-dose methimazole (2.5-5 mg daily) beyond the standard duration has been shown to significantly reduce recurrence rates 6
- Hyperthyroidism relapses in approximately 50% of patients after discontinuation of standard therapy 5
- For patients with recurrent disease, ablative therapy (radioiodine or surgery) should be considered 5
Potential Side Effects and Monitoring
- Monitor for agranulocytosis, which typically presents with sore throat and fever; if these symptoms develop, obtain a complete blood count and discontinue methimazole 3
- Other potential side effects include hepatitis, vasculitis, and thrombocytopenia 3
- Mild hepatotoxicity is more common with propylthiouracil than with methimazole 4
- Lower doses of methimazole (15 mg/day) have significantly fewer adverse effects compared to higher doses (30 mg/day) 4