What is the recommended dosage of Methimazole for treating hyperthyroidism?

Recommended Dosage of Methimazole for Hyperthyroidism

The recommended initial daily dosage of methimazole for treating hyperthyroidism is 15 mg for mild disease, 30-40 mg for moderately severe disease, and 60 mg for severe hyperthyroidism, divided into 3 doses at 8-hour intervals, with a maintenance dosage of 5-15 mg daily. 1

Initial Dosing Based on Disease Severity

• For mild hyperthyroidism: 15 mg daily initially 1
• For moderately severe hyperthyroidism: 30-40 mg daily initially 1
• For severe hyperthyroidism: 60 mg daily initially 1
• The initial dose is typically divided into 3 doses given at 8-hour intervals 1

Maintenance Dosing

• After achieving control of hyperthyroidism, the maintenance dose ranges from 5-15 mg daily 1
• The goal of therapy is to maintain free T4 or Free T4 Index (FTI) in the high-normal range using the lowest possible thioamide dosage 2

Pediatric Dosing

• Initial pediatric dosage: 0.4 mg/kg of body weight daily, divided into 3 doses given at 8-hour intervals 1
• Maintenance pediatric dosage: approximately half of the initial dose 1

Monitoring Recommendations

• Monitor free T4 or FTI every 2-4 weeks during the initial treatment phase 2
• Once stabilized, continue monitoring to adjust dosage as needed to maintain euthyroid state 3
• Patients typically achieve euthyroid status within 5-6 weeks of starting treatment 4

Alternative Dosing Regimens

• Single daily dosing of 15 mg methimazole has been shown to be effective in controlling hyperthyroidism in most patients with Graves' disease 4
• Single daily dosing may cause fewer adverse effects compared to higher doses 4
• Studies show that 93% of patients treated with a single daily dose of 15 mg achieve euthyroidism within 12 weeks 4

Special Considerations

• For pregnant patients, propylthiouracil (PTU) is preferred over methimazole during the first trimester due to lower risk of birth defects 2
• Women treated with methimazole can breastfeed safely 2
• Beta-blockers (e.g., propranolol, atenolol) can be used as adjunctive therapy to control symptoms until methimazole reduces thyroid hormone levels 2, 3

Potential Side Effects and Monitoring

• Monitor for agranulocytosis, which typically presents with sore throat and fever 2
• If symptoms of agranulocytosis develop, obtain a complete blood count and discontinue methimazole 2
• Side effects appear to be dose-related, with higher incidence at doses of 30 mg daily compared to 15 mg daily 4

Intravenous Administration in Special Circumstances

• For patients unable to take oral medication (e.g., ileus, severe vomiting, emergency surgery), intravenous methimazole may be considered 5
• This is a rare but viable option for refractory cases when oral or rectal administration is not possible 5