How to adjust Propylthiouracil (PTU) dosing in a patient with thyroid storm?

PTU Dosing in Thyroid Storm

In thyroid storm, administer propylthiouracil (PTU) at high initial doses of 600-900 mg orally, followed by 200-250 mg every 4-6 hours, as PTU is preferred over methimazole due to its additional ability to block peripheral conversion of T4 to T3. 1, 2

Initial Loading Dose

• Start with 600-900 mg PTU orally as the loading dose in severe hyperthyroidism or thyroid storm 2
• The FDA label indicates that occasional patients require 600-900 mg daily initially for severe hyperthyroidism 2
• PTU is the preferred thionamide because it uniquely inhibits both thyroid hormone synthesis AND peripheral T4 to T3 conversion, which is critical in thyroid storm 1, 2

Maintenance Dosing

• Administer 200-250 mg PTU every 4-6 hours (approximately every 4 hours in acute storm) after the loading dose 1, 2
• The total daily dose typically ranges from 600-900 mg divided into doses given at approximately 8-hour intervals, though more frequent dosing (every 4 hours) is often used in thyroid storm 2
• Continue high-dose therapy until clinical improvement and thyroid hormone levels begin to decline 1

Critical Timing Considerations

• Administer PTU BEFORE giving iodine therapy (potassium iodide or sodium iodide) 1
• Wait 1-2 hours after starting PTU before administering iodine to prevent worsening thyrotoxicosis 1
• This sequence is essential because iodine given before thionamides can paradoxically worsen thyroid storm by providing substrate for additional hormone synthesis 1

Alternative Routes When Oral Administration Fails

• Consider rectal administration if the patient cannot take oral medications due to altered mental status, vomiting, or gastrointestinal obstruction 3
• Rectal PTU shows substantial absorption with demonstrated therapeutic efficacy in thyroid storm 3
• This route provides a practical alternative when parenteral options are unavailable 3

Adjunctive Therapy (Must Be Given Concurrently)

• Beta-blockers: Propranolol 60-80 mg orally every 4-6 hours, or esmolol infusion (loading 0.5 mg/kg IV over 1 minute, then 50-300 mcg/kg/min) for hemodynamically unstable patients 1
• Corticosteroids: Dexamethasone or hydrocortisone to block peripheral T4 to T3 conversion and treat relative adrenal insufficiency 1, 4
• Iodine: Saturated potassium iodide solution 1-2 hours AFTER starting PTU 1

Monitoring and Dose Adjustment

• Monitor thyroid function (free T4, free T3, TSH) every 2-3 weeks after initial stabilization 1
• Watch for transition to hypothyroidism, which commonly occurs after thyroid storm treatment 1
• Monitor for agranulocytosis, a serious complication of thionamide therapy 1
• Once stabilized, taper to maintenance doses of 100-150 mg daily 2

Special Situations Requiring Alternative Management

• If PTU is not tolerated (e.g., agranulocytosis, severe hepatotoxicity, angioedema), switch to methimazole or consider emergent thyroidectomy 5, 6
• If both thionamides fail or cannot be used, therapeutic plasma exchange (TPE) is an effective salvage therapy that directly removes circulating thyroid hormones 5
• Recurrence of thyroid storm can occur if corticosteroids are discontinued prematurely; maintain dexamethasone until full clinical resolution 4

Common Pitfalls to Avoid

• Never give iodine before PTU - this can worsen the storm by providing substrate for more hormone synthesis 1
• Do not use beta-blockers alone without thionamides - they only treat symptoms, not the underlying excess hormone production 1
• Do not discontinue corticosteroids too early - premature withdrawal can trigger recurrence of thyroid storm 4
• Do not delay treatment waiting for confirmatory labs - thyroid storm is a clinical diagnosis requiring immediate empiric therapy 1