Maximum Dose of Propylthiouracil (PTU)
The maximum daily dose of propylthiouracil (PTU) is 900 mg per day for adults, as indicated in the FDA drug labeling. 1
Dosing Guidelines for Adults
PTU is administered orally with the following dosing recommendations:
- Initial dose: 300 mg daily (standard starting dose)
- For severe hyperthyroidism or large goiters: 400 mg daily initially
- For particularly severe cases: 600-900 mg daily initially
- Maintenance dose: 100-150 mg daily
- Administration: Total daily dose is usually divided into 3 equal doses given approximately every 8 hours
Special Populations
Pediatric Patients
- PTU is generally not recommended for pediatric use except in rare instances when other therapies are not appropriate
- Severe liver injury has been reported with doses as low as 50 mg/day, but most cases were associated with doses of 300 mg/day and higher 1, 2
- When used in children, dosing typically starts at 50 mg daily with careful upward titration based on clinical response and thyroid function tests 1
Geriatric Patients
- Dose selection should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function
- Start at the lower end of the dosing range 1
Pregnant and Lactating Women
- PTU is preferred over methimazole during early gestation 2
- During lactation, doses not exceeding 150 mg daily appear safe for breastfeeding mothers 3
Clinical Considerations
Efficacy of Different Dosing Regimens
- High-dose regimens (500-1200 mg/day) have been associated with higher remission rates (75.4%) compared to conventional lower-dose regimens (100-300 mg/day, 41.6% remission) in some studies 4
- However, higher doses carry increased risk of adverse effects, particularly hepatotoxicity 2
Maintenance Therapy
- Some studies suggest that minimum maintenance doses (as low as 50 mg every other day) for 6 months can be effective in predicting remission in Graves' disease 5
Comparative Efficacy
- When comparing single daily dosing, 15 mg of methimazole has been shown to be more effective than 150 mg of PTU in inducing euthyroidism 6
Safety Concerns
Hepatotoxicity
- PTU can cause severe liver injury, including acute liver failure
- Risk appears to be dose-dependent, with most cases occurring at doses of 300 mg/day or higher 2
- Duration of therapy is also a risk factor, with most adult cases occurring after 4 months to more than 1 year of treatment 2
Monitoring
- Regular monitoring of liver function is recommended, especially with higher doses
- Patients should be educated about signs and symptoms of hepatotoxicity
Key Takeaways
- Maximum dose: 900 mg daily for adults
- Standard initial dose: 300 mg daily
- Standard maintenance dose: 100-150 mg daily
- Higher doses carry increased risk of hepatotoxicity
- Divided dosing (three times daily) is standard practice
- PTU should be used with caution in special populations, particularly children