What is the recommended dose of Propylthiouracil (PTU) in a thyroid storm?

PTU Dosing in Thyroid Storm

For thyroid storm, administer propylthiouracil (PTU) 200 mg orally every 4-6 hours (800-1200 mg daily in divided doses), as this is the preferred thionamide due to its dual mechanism of blocking both thyroid hormone synthesis and peripheral conversion of T4 to T3. 1

Why PTU is Preferred Over Methimazole

PTU should be used as the first-line thionamide in thyroid storm specifically because it provides two critical therapeutic actions 1:

• Blocks thyroid hormone synthesis at the thyroid gland level
• Inhibits peripheral conversion of T4 to T3, which is the more metabolically active hormone driving the crisis 2, 3

This dual mechanism makes PTU superior to methimazole in life-threatening thyroid storm, even though methimazole is generally preferred for routine hyperthyroidism management 2.

Complete Treatment Algorithm for Thyroid Storm

Step 1: Block Thyroid Hormone Synthesis (Immediate)

• PTU 200 mg orally every 4-6 hours 4
• Alternative: Methimazole 40 mg every 6 hours if PTU unavailable 1

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

• Saturated potassium iodide solution or sodium iodide 1-2 hours AFTER starting thionamides 1
• Critical pitfall: Never give iodine before thionamides, as this can worsen thyrotoxicosis by providing substrate for more hormone synthesis 1

Step 3: Control Adrenergic Symptoms (Concurrent)

• Propranolol 60-80 mg orally every 4-6 hours for stable patients 1
• Esmolol 500 mcg/kg IV bolus over 1 minute, then 50 mcg/kg/min infusion for hemodynamically unstable patients, titrating up to 300 mcg/kg/min as needed 1
• Propranolol has the added benefit of blocking peripheral T4 to T3 conversion 1

Step 4: Reduce Peripheral T4 to T3 Conversion

• Dexamethasone or hydrocortisone to further block peripheral conversion and treat potential relative adrenal insufficiency 1

Step 5: Supportive Care

• Oxygen therapy, antipyretics for fever control, IV fluids, and treatment of precipitating factors 1

Monitoring During Treatment

• Monitor thyroid function (free T4, T3, TSH) every 2-3 weeks after initial stabilization 1
• Watch for rapid clinical improvement: PTU causes considerable decrease in serum T3 within days, accompanied by improvements in metabolic rate 5
• Watch for transition to hypothyroidism, which commonly occurs after thyroid storm treatment 1

Critical Safety Considerations

PTU-Specific Toxicity

• Monitor for acute hepatitis: PTU can cause potentially fatal hepatotoxicity with elevated ALT, bilirubin, and ALP 4
• Monitor for agranulocytosis: Check CBC if fever or sore throat develops 1
• If PTU toxicity develops, switch to methimazole or consider therapeutic plasma exchange 6

When PTU Fails or Cannot Be Used

• Therapeutic plasma exchange (TPE) is an effective rescue therapy when conventional treatments fail 6
• TPE removes T3, T4, autoantibodies, and catecholamines, normalizing thyroid hormones within 4 daily treatments 6

Tapering Strategy After Stabilization

Once the patient stabilizes (typically 48-72 hours of controlled heart rate and blood pressure) 7:

1. Taper beta-blockers first by 25% every 2-3 days once HR <90 bpm consistently 7
2. Maintain full PTU doses until free T4 and T3 approach upper limit of normal 7
3. Discontinue iodine abruptly within 3-5 days rather than tapering 7
4. Monitor thyroid function every 2-3 weeks during tapering phase 7

Special Populations

Pregnancy

• PTU is preferred over methimazole in pregnant women with thyroid storm 2
• Treatment protocol is similar to non-pregnant patients with fetal monitoring 1