What is the best course of action for a patient with hyperthyroidism experiencing fatigue, hypotension, and bradycardia while taking 50mg of Propylthiouracil (PTU) per day?

Immediate Management: Suspect PTU-Induced Hypothyroidism

This patient is exhibiting classic signs of iatrogenic hypothyroidism from PTU overtreatment—immediately discontinue or significantly reduce PTU dosing and check urgent thyroid function tests (TSH, free T4, free T3). 1

Clinical Presentation Analysis

The constellation of symptoms strongly suggests PTU has overcorrected the hyperthyroidism into hypothyroidism:

• Bradycardia (62 bpm) is characteristic of hypothyroidism, not hyperthyroidism which typically causes tachycardia 1
• Hypotension (90/50 mmHg) aligns with hypothyroidism's decreased cardiac output and bradycardia 1
• Fatigue is a cardinal symptom of hypothyroidism 1

The hemodynamic profile is opposite to what hyperthyroidism produces—hyperthyroidism causes increased heart rate, increased cardiac output, and typically normal-to-elevated blood pressure 1.

Immediate Actions Required

Step 1: Medication Management

• Hold PTU immediately until thyroid function tests return 1
• The current dose of 50 mg daily is at the lower end of maintenance dosing (usual maintenance 100-150 mg daily), but individual sensitivity varies 2

Step 2: Urgent Laboratory Testing

• Measure TSH, free T4, and free T3 within 24-48 hours to confirm hypothyroidism 3
• If TSH is elevated with low free T4/T3, this confirms PTU-induced hypothyroidism 1

Step 3: Cardiovascular Assessment

• Obtain ECG to evaluate for bradyarrhythmias or other conduction abnormalities 1
• Monitor blood pressure closely—severe hypothyroidism can cause hemodynamic compromise 1

Treatment Algorithm Based on Test Results

If Hypothyroid (High TSH, Low Free T4/T3):

• Discontinue PTU completely 1
• Initiate levothyroxine replacement therapy:
  • Young, healthy patients: Start full replacement dose of 1.6 mcg/kg daily 1
  • Elderly or those with cardiovascular disease: Start reduced dose of 25-50 mcg daily 1
• Recheck TSH and free T4 in 6-8 weeks and adjust dose accordingly 1

If Euthyroid (Normal TSH, Normal Free T4/T3):

• Reduce PTU dose by 50% (to 25 mg daily) 2
• Recheck thyroid function in 2-4 weeks 3
• Consider that symptoms may represent non-thyroidal illness

If Still Hyperthyroid (Low TSH, High Free T4/T3):

• This scenario is unlikely given the clinical presentation 1
• If confirmed, consider alternative diagnoses for bradycardia and hypotension (e.g., beta-blocker use, cardiac disease) 1

Critical Pitfalls to Avoid

• Do not continue current PTU dosing without investigation—the clinical picture strongly suggests overtreatment 1
• Do not assume hyperthyroidism persists based solely on the original diagnosis—PTU can rapidly induce hypothyroidism 1
• Do not overlook PTU-induced autoimmune complications—though rare, PTU can cause severe autoimmune disease requiring immunosuppression 4
• Do not delay thyroid function testing—waiting could worsen hemodynamic compromise in severe hypothyroidism 1

Monitoring After Intervention

• Weekly clinical assessment until symptoms resolve 3
• Repeat thyroid function tests every 6-8 weeks after initiating levothyroxine (if hypothyroid) 1
• Adjust levothyroxine by 12.5-25 mcg increments if TSH remains above reference range 1
• Once stable, monitor annually or sooner if clinical status changes 1

Long-Term Considerations

If PTU-induced hypothyroidism is confirmed, the patient will likely need permanent thyroid hormone replacement, as spontaneous recovery is uncommon once hypothyroidism develops during antithyroid drug therapy 1. Alternative definitive treatments for the original hyperthyroidism (radioactive iodine or surgery) should be discussed once the patient is stabilized 1, 3.