Default Dosage of Thyrozol (Propylthiouracil) for Hyperthyroidism
The standard initial dosage of propylthiouracil (Thyrozol) for adults with hyperthyroidism is 300 mg daily, typically divided into 3 equal doses of 100 mg taken at 8-hour intervals. 1
Dosage Guidelines
Adult Dosing
- Initial dose: 300 mg daily divided into 3 equal doses (100 mg every 8 hours)
- Severe hyperthyroidism or large goiter: May increase to 400 mg daily initially; occasionally up to 600-900 mg daily
- Maintenance dose: 100-150 mg daily once stabilized 1
Special Populations
- Elderly patients: Start with lower doses due to potential decreased hepatic, renal, or cardiac function 1
- Pregnant women: The goal is to maintain FT4 or FTI in the high-normal range using the lowest possible thioamide dosage, with monitoring every 2-4 weeks 2
Administration Considerations
- Propylthiouracil should be administered in divided doses rather than a single daily dose for optimal efficacy
- Research shows that divided dosing (every 8 hours) is significantly more effective than single daily dosing 3
- In one study, patients receiving propylthiouracil in divided doses (150 mg every 8 hours) had better response rates than those receiving a single daily dose of 450 mg 3
Monitoring and Adjustments
- Monitor FT4 or FTI every 2-4 weeks during initial treatment 2
- Adjust dosage based on thyroid function tests
- Beta blockers (e.g., propranolol) can be used concurrently to manage symptoms until thioamide therapy reduces thyroid hormone levels 2
Important Cautions
- Side effects to monitor: Agranulocytosis (presents with sore throat and fever), hepatitis, vasculitis, and thrombocytopenia 2
- If symptoms of agranulocytosis develop, obtain a complete blood count and discontinue the medication 2
- Propylthiouracil is generally not recommended for pediatric patients except in rare instances where other therapies are not appropriate 1
- Cases of severe liver injury have been reported with doses as low as 50 mg/day, but most cases were associated with doses of 300 mg/day and higher 1
Treatment Response
- Response to divided dosage schedules is typically prompt and predictable
- Most patients achieve remission within 10 weeks on a properly divided dosing schedule 3
- Poor response to treatment may indicate non-compliance rather than medication resistance 4
Remember that the goal of treatment is to achieve euthyroidism with the lowest effective dose to minimize side effects while controlling hyperthyroid symptoms.