What are the recommended dosages of propranolol (beta blocker) and propylthiouracil (PTU) (thyroid inhibitor) in an impending thyroid storm?

Dosage of Propranolol and PTU in Impending Thyroid Storm

For impending thyroid storm, administer propranolol 60-80 mg orally every 4-6 hours and propylthiouracil (PTU) 200 mg orally every 4-6 hours as first-line therapy. 1

Beta-Blocker Dosing

Oral Propranolol (Preferred Route)

• Standard dosing: 60-80 mg orally every 4-6 hours for controlling adrenergic symptoms and blocking peripheral conversion of T4 to T3 1
• Propranolol has the dual advantage of controlling tachycardia while also inhibiting peripheral conversion of T4 to the more active T3, making it the most widely studied and preferred beta-blocker for thyroid storm 1
• Alternative oral dosing ranges from 40-160 mg daily in divided doses, though higher and more frequent dosing (every 4-6 hours) is typically needed in thyroid storm 2

Intravenous Esmolol (For Hemodynamic Instability)

• Loading dose: 500 mcg/kg (0.5 mg/kg) IV over 1 minute 1
• Maintenance infusion: Start at 50 mcg/kg/min, titrate up to maximum 300 mcg/kg/min as needed for heart rate control 1
• Esmolol is preferred when hemodynamic instability requires careful titration due to its ultra-short half-life, allowing rapid reversal if cardiovascular collapse occurs 1
• If inadequate response, give second loading bolus of 0.5 mg/kg over 1 minute and increase maintenance to 100 mcg/kg/min 1

Alternative: Calcium Channel Blockers

• If beta-blockers are contraindicated (severe asthma, decompensated heart failure), use diltiazem 15-20 mg (0.25 mg/kg) IV over 2 minutes, then 5-15 mg/h maintenance infusion 1

Propylthiouracil (PTU) Dosing

Standard PTU Regimen

• 200 mg orally every 4-6 hours (800 mg daily total) 3, 4, 5
• PTU is preferred over methimazole in thyroid storm because it blocks both thyroid hormone synthesis AND peripheral conversion of T4 to T3 1
• Administer PTU first, before any iodine therapy 1

Critical Timing Consideration

• Never administer iodine before starting PTU - this can paradoxically worsen thyrotoxicosis by providing substrate for additional thyroid hormone synthesis 1
• Wait 1-2 hours after initiating PTU before giving potassium iodide or sodium iodide 1

Complete Treatment Algorithm

Step 1: Initiate PTU Immediately

• PTU 200 mg orally every 4-6 hours 3, 4, 5

Step 2: Start Beta-Blockade

• Propranolol 60-80 mg orally every 4-6 hours (if stable) 1
• OR Esmolol IV infusion (if hemodynamically unstable) 1

Step 3: Block Hormone Release (1-2 Hours After PTU)

• Saturated potassium iodide solution or sodium iodide 1

Step 4: Reduce Peripheral Conversion

• Dexamethasone or hydrocortisone to block T4 to T3 conversion and treat possible relative adrenal insufficiency 1, 3, 4
• Hydrocortisone was successfully used in case reports 3, 4

Step 5: Supportive Care

• Antipyretics for fever control 1
• Oxygen therapy as needed 1
• IV fluids for hydration 1
• Identify and treat precipitating factors 1

Critical Monitoring Parameters

Cardiovascular Monitoring

• Continuous cardiac monitoring with serial blood pressure and heart rate every 5-15 minutes during esmolol titration 1
• Monitor for hypotension, bradycardia, and heart failure 1
• Target ScvO2 >70% and cardiac index 3.3-6.0 L/min/m² in critically ill patients 1

Hepatic Monitoring

• Monitor liver function closely with PTU use - acute hepatitis is a rare but potentially fatal complication 5
• One case report documented ALT rising to 852 U/l after 2 weeks of PTU 200 mg four times daily, requiring immediate discontinuation 5
• Check liver enzymes, bilirubin, and INR regularly during PTU therapy 5

Hematologic Monitoring

• Monitor for agranulocytosis with thionamide use 1

Important Safety Considerations

Beta-Blocker Contraindications

• Absolute contraindications: second or third-degree heart block, decompensated heart failure, asthma/obstructive airway disease 2
• However, beta-blockers should still be administered in thyroid storm even with concurrent pulmonary embolus, as long as there is no evidence of heart strain 6
• Use with caution in diabetes as propranolol masks hypoglycemia symptoms 2

PTU-Specific Warnings

• Acute hepatitis can develop, requiring immediate discontinuation 5
• Be vigilant for interactions between regular paracetamol use and PTU, which may predispose to liver impairment 5
• Despite hepatotoxicity risk, PTU remains preferred over methimazole in thyroid storm due to its dual mechanism 1

Pregnancy Considerations

• The treatment protocol is similar in pregnant patients 1
• Case reports confirm successful use of propranolol and PTU during pregnancy and peripartum thyroid storm 3
• Monitor fetal status and avoid delivery during active thyroid storm unless absolutely necessary 1

Clinical Pitfalls to Avoid

• Never give iodine before PTU - this is the most critical error that can worsen the crisis 1
• Do not abruptly discontinue propranolol after chronic use, as this causes rebound tachycardia 2
• Do not withhold beta-blockers solely due to concurrent conditions like pulmonary embolus if no heart strain is present 6
• Recent evidence shows beta-1 selective beta-blockers (like esmolol) have equivalent mortality to propranolol, so either can be used based on clinical context 7