Recommended Dosage for Propylthiouracil (PTU)
The recommended initial dose of propylthiouracil for adults with hyperthyroidism is 300 mg daily, typically divided into three equal doses given at approximately 8-hour intervals. 1
Adult Dosing
- Initial dose is 300 mg daily (divided into three equal doses of 100 mg every 8 hours) 1
- For patients with severe hyperthyroidism or very large goiters, the initial dose may be increased to 400 mg daily; occasionally patients may require 600-900 mg daily initially 1
- Maintenance dose is typically 100-150 mg daily once euthyroidism is achieved 1
- Doses should be adjusted based on thyroid function tests (TSH, free T4) to maintain the patient in a euthyroid state 2
Special Populations
Pediatric Patients
- PTU is generally not recommended for pediatric patients except in rare instances when other therapies are not appropriate 1
- For children 6 years or older, when PTU must be used, start with 50 mg daily with careful upward titration based on clinical response and thyroid function tests 1
- Note that severe liver injury has been reported with doses as low as 50 mg/day, though most cases were associated with doses of 300 mg/day and higher 1
Geriatric Patients
- Dose selection should be cautious, reflecting the greater frequency of decreased hepatic, renal, or cardiac function 1
- Start at the lower end of the dosing range and monitor closely 1
Pregnant Women
- PTU is preferred over methimazole during the first trimester of pregnancy due to lower risk of birth defects 2
- The goal is to maintain free T4 or free T4 index in the high-normal range using the lowest possible thioamide dosage 2
- Monitor thyroid function every 2-4 weeks during pregnancy 2
Monitoring and Dose Adjustment
- Measure free T4 or free T4 index every 2-4 weeks during initial therapy to guide dose adjustments 2
- Once stable, thyroid function tests can be performed less frequently 2
- Continue monitoring for potential side effects, particularly hepatotoxicity 3
Important Considerations
- PTU has been shown to be less effective than methimazole when given as a single daily dose; therefore, divided dosing is recommended 4
- PTU not only blocks thyroid hormone synthesis but also inhibits peripheral conversion of T4 to T3, which may be beneficial in severe hyperthyroidism 5
- Compliance issues should be considered in patients who do not respond to appropriate doses; noncompliance is the most likely reason for treatment failure 6
- Hepatic injury occurs in approximately 28% of patients on PTU but is usually subclinical and transient 3
Precautions
- Monitor liver function tests before therapy and periodically during treatment 3
- Discontinue PTU at least 4 days before radioactive iodine therapy if that treatment is planned, as PTU pretreatment is associated with higher failure rates of radioactive iodine therapy 7
- Be alert for signs of agranulocytosis (sore throat, fever), which requires immediate discontinuation of the medication and complete blood count evaluation 2
Remember that the goal of therapy is to maintain the patient in a euthyroid state using the lowest effective dose of medication to minimize adverse effects.