Propylthiouracil Dosing for Toxic Multinodular Goiter
For adults with toxic multinodular goiter requiring short-term bridge therapy before definitive treatment, start propylthiouracil at 300 mg daily divided into three equal doses given every 8 hours, with a usual maintenance dose of 100-150 mg daily once euthyroid. 1
Initial Dosing Strategy
- Standard starting dose is 300 mg daily in three divided doses (100 mg every 8 hours) for most adults with hyperthyroidism 1
- For severe hyperthyroidism or very large goiters, the initial dose may be increased to 400 mg daily 1
- Occasional patients may require 600-900 mg daily initially, though higher doses carry increased hepatotoxicity risk 1
Maintenance and Duration
- Once euthyroid, reduce to maintenance dose of 100-150 mg daily 1
- For toxic multinodular goiter specifically, do not rely on prolonged antithyroid drug therapy expecting remission—unlike Graves' disease, toxic multinodular goiter represents autonomous hyperfunctioning nodules that will not remit with medical therapy alone 2
- PTU serves only as bridge therapy to control hyperthyroidism before definitive treatment with radioiodine or surgery 2, 3
Critical Timing Before Definitive Treatment
If proceeding to radioiodine therapy, discontinue PTU at least 7 days before RAI administration to avoid treatment failure 4. This is crucial because:
- PTU discontinued only 4-7 days before RAI is associated with a 29% failure rate versus 9% with RAI alone (P=0.039) 4
- Even discontinuation for 1 week still shows nearly 2-fold increased failure rate (17% vs 9%) 4
- The radioprotective effect of PTU significantly reduces RAI efficacy 4
Important Safety Considerations
- PTU carries risk of severe liver failure requiring transplantation or causing death, making it generally not recommended as first-line therapy except in specific situations 5
- Most cases of severe liver injury occurred with doses of 300 mg/day or higher, though cases have been reported with doses as low as 50 mg/day 1
- Monitor for agranulocytosis symptoms (sore throat, fever) and obtain complete blood count if these develop, then discontinue PTU immediately 6
- Other serious adverse effects include hepatitis, vasculitis, and thrombocytopenia 6
Definitive Treatment Planning
Radioiodine therapy should be the first-line definitive treatment for geriatric patients with toxic multinodular goiter, showing 83% response rates (euthyroid or hypothyroid) at one year 7. For younger patients or those with compressive symptoms:
- Surgery (total thyroidectomy) provides immediate permanent cure with no recurrences and is preferred for obstructive symptoms, substernal extension, or cosmetic concerns 2
- RAI is less effective for substernal goiters where surgery provides definitive decompression 2