Propylthiouracil Dosing for Hyperthyroidism
For adults with hyperthyroidism, start PTU at 300 mg daily divided into three equal doses given every 8 hours, with a maintenance dose of 100-150 mg daily once euthyroid. 1
Standard Adult Dosing
- Initial dose: 300 mg daily divided into three equal doses at approximately 8-hour intervals 1
- For severe hyperthyroidism or very large goiters, increase the initial dose to 400 mg daily; occasionally patients require 600-900 mg daily initially 1
- Maintenance dose: 100-150 mg daily after achieving euthyroidism 1
- The goal is maintaining free T4 or free thyroxine index in the high-normal range using the lowest possible dose 2
Monitoring During Treatment
- Check thyroid function every 2-4 weeks during dose titration 2
- Once stable on maintenance therapy, monitoring frequency can be reduced 2
- Obtain CBC immediately and discontinue PTU if agranulocytosis is suspected (fever, sore throat, infection) 2
- Monitor for hepatitis, vasculitis, and thrombocytopenia throughout treatment 2
Special Population: Pregnancy
PTU is the preferred antithyroid drug in pregnancy, particularly during the first trimester 2
- Use the lowest possible dose to maintain FT4 or FTI in the high-normal range 2
- Beta blockers can be added temporarily for symptom control until thyroid hormone levels decrease 2
- Monitor thyroid function every trimester once stable 2
- Women can safely breastfeed while taking PTU 2
Pediatric Considerations
- PTU is generally not recommended in pediatric patients except when alternative therapies are inappropriate 1
- For patients 6 years or older, if PTU must be used, initiate at 50 mg daily with careful upward titration based on TSH and free T4 levels 1
- Most severe liver injury cases in children occurred with doses ≥300 mg/day, though cases have been reported with doses as low as 50 mg/day 1
Geriatric Dosing
- Use cautious dose selection in elderly patients due to greater frequency of decreased hepatic, renal, or cardiac function 1
- Start at the lower end of the dosing range and monitor closely 1
Critical Care: Thyroid Storm
- PTU is part of the standard drug series for thyroid storm management 2
- Use in combination with propranolol, iodide solutions, and dexamethasone following emergency protocols 2
Important Clinical Caveats
PTU has inferior efficacy compared to methimazole when using once-daily dosing regimens. A single daily dose of 150 mg PTU was significantly less effective than 15 mg methimazole in achieving euthyroidism (19.4% vs 77.1% achieving normal T3 and T4 levels) 3, 4. Therefore, PTU must be given in divided doses three times daily to maintain therapeutic efficacy 1.
PTU pretreatment reduces radioiodine therapy efficacy. If patients pretreated with PTU require subsequent radioiodine therapy, discontinue PTU for more than 4 months before 131I administration to restore cure rates to baseline (24% cure rate when stopped 5-55 days before vs 66% with no prior ATD) 5. This effect is specific to PTU and does not occur with methimazole 5.