Amiodarone is a class III anti-arrhythmic for tachyarrhythmias

Although most patients remain euthyroid on amiodarone, 4-18% develop thyroid disease months to years after exposure.

Amiodarone-induced thyroid disease occurs because amiodarone is structurally similar to triiodothyronine and thyroxine and each 200mg tablet contains 75 mg of iodine.

Two types of amiodarone-induced thyroid disease:

• Amiodarone-induced hypothyroidism (AIH)
• Amiodarone-induced thyrotoxicosis (AIT)

Amiodarone-induced hypothyroidism (AIH)

• Presents with subtle to overt hypothyroidism 
• Treat by discontinuing amiodarone; thyroid recovers within 3 months
• If amiodarone cannot be discontinued, start levothyroxine

Amiodarone-induced thyrotoxicosis (AIT)

• Sudden symptom onset months to years following exposure; mean 2-47 months post-exposure
• Can be a life-threatening presentation (similar to thyroid storm) with severe cardiac manifestations and hemodynamic instability
• Treatment (treat like thyroid storm, if severe)
  • Discontinue drug, if possible
  • Thionamides (inhibit enzyme producing thyroid hormones)
  • Methimazole or propylthiouracil
  • Beta-blockers
  • Steroids
  • Airway and hemodynamic support

References

Padmanabhan H. Amiodarone and Thyroid Dysfunction. South Med J. 2010 Sep; 103 (9): 922-30

Follow me on Twitter @criticalcarenow