In which clinical situations is amiodarone contraindicated?

Absolute Contraindications to Amiodarone

Amiodarone is absolutely contraindicated in patients with second- or third-degree AV block or marked sinus bradycardia unless a functioning pacemaker is in place, as well as in those with known hypersensitivity to amiodarone or iodine, and in patients with cardiogenic shock. 1

Cardiac Conduction Contraindications

The most critical contraindication involves cardiac conduction abnormalities:

• Second- or third-degree AV block without a pacemaker - This is an absolute contraindication for both IV and oral formulations 2, 1
• Marked sinus bradycardia without a pacemaker - IV amiodarone causes bradycardia in 4.9% of patients and can be progressive and fatal 2, 1
• Sinoatrial block - Listed as a major contraindication to IV administration 3

The rationale is straightforward: amiodarone causes bradycardia and heart block in 1-3% of patients receiving oral therapy and 4.9% receiving IV therapy 2. Without pacemaker backup, these conduction disturbances can progress to complete heart block or fatal bradycardia.

Other Absolute Contraindications

• Cardiogenic shock - Listed explicitly in FDA labeling 1
• Known hypersensitivity to amiodarone, iodine, or any component - Standard drug allergy contraindication 1

Relative Contraindications and High-Risk Situations

While not absolute contraindications, these situations require extreme caution or alternative therapy:

Severe Hypotension

• Hypotension is the most common adverse effect (16% of patients) 1
• Can be refractory and fatal in some cases 1
• If hypotension occurs, slow or discontinue the infusion 1

Severe Respiratory Failure

• Listed as a contraindication to IV administration 3
• Risk of acute-onset pulmonary toxicity (days to weeks) including ARDS, which occurred in 2% of patients in clinical trials 1
• Patients with pre-existing abnormal chest X-rays are at particular risk for pulmonary fibrosis 4

Hepatocellular Failure

• Acute hepatocellular necrosis leading to hepatic coma and death has been reported with high-dose IV loading 1
• Listed as a contraindication to IV use 3
• However, recent data suggests amiodarone may be reasonable in cirrhosis patients with close monitoring if benefits outweigh risks 5

Hyperthyroidism

• Listed as a contraindication 3
• Risk of arrhythmia breakthrough or exacerbation that may result in death 1
• Both hypothyroidism and hyperthyroidism can develop during therapy (hypothyroidism 6%, hyperthyroidism 0.9-2%) 6

Pregnancy and Breastfeeding

• Category D drug - contraindicated in pregnant and breastfeeding women 7

Critical Drug Interactions Creating Relative Contraindications

QT-prolonging drugs: Combination with other QT-prolonging agents (fluoroquinolones, macrolides, azoles, other antiarrhythmics) should be reserved only for life-threatening arrhythmias unresponsive to single agents, as this increases torsades de pointes risk 1

Common Pitfalls

• Don't assume baseline liver enzyme elevations are a contraindication - 54% of patients have baseline elevations, and 81% either improve or remain stable during therapy 1. However, progressive hepatic injury requires dose reduction or discontinuation.

• Elderly patients (>70 years) are at particular risk for hypothyroidism - Four of five hypothyroid patients in one series were over 70 4

• The "contraindication" label for hepatic dysfunction is nuanced - While severe hepatocellular failure is contraindicated, compensated cirrhosis may be manageable with close monitoring 5