What are the indications, dosing, and monitoring requirements for Amiodarone (antiarrhythmic medication) in treating life-threatening arrhythmias?

Amiodarone: Indications, Dosing, and Monitoring Requirements

Amiodarone is indicated for life-threatening ventricular arrhythmias, including ventricular fibrillation and hemodynamically unstable ventricular tachycardia, as well as for refractory atrial fibrillation when other treatments have failed, with dosing requiring a loading phase followed by maintenance therapy and comprehensive monitoring for multiple organ toxicities. 1, 2

Indications

Primary Indications

• Life-threatening ventricular arrhythmias (ventricular fibrillation, hemodynamically unstable ventricular tachycardia)
• Refractory atrial fibrillation/flutter when other treatments have failed
• Adjunctive therapy to reduce ICD shocks in patients with implantable cardioverter defibrillators
• Treatment of electrical storm

Contraindications

• Hypersensitivity to amiodarone or iodine
• Cardiogenic shock
• Marked sinus bradycardia
• Second- or third-degree AV block without a functional pacemaker
• Pregnancy and lactation 1

Dosing Regimens

Intravenous Administration (Acute/Life-threatening situations)

• Loading dose: 150 mg over 10 minutes for breakthrough VF or unstable VT
• First 24 hours: 1000 mg total, administered as:
  • Initial rapid infusion: 5 mg/kg over 1 hour (or over 15 minutes in life-threatening situations)
  • Followed by: Slow infusion of remaining first-day dose
• Maintenance infusion: 0.5 mg/min (720 mg/24 hours) 2

Oral Administration

• Loading dose options:
  1. 600 mg twice daily for 7 days, then 400-600 mg daily 1
  2. 1.2-1.8 g/day divided until 10 g total is reached (hospitalized patients)
  3. 600-800 mg/day divided until 10 g total is reached (ambulatory patients)
• Maintenance dose: 200-400 mg daily (lowest effective dose) 1

Monitoring Requirements

Baseline Assessment (Before Starting Therapy)

• Thyroid function tests (TSH, free T4, T3)
• Liver function tests (AST, ALT)
• Pulmonary function tests with DLCO
• Chest imaging
• Ophthalmologic examination
• ECG with QT interval measurement
• Serum digoxin levels (if applicable)
• Prothrombin time/INR (if on anticoagulants)

Ongoing Monitoring Schedule

Test	Frequency	Comments
Thyroid function tests	Every 6 months	Include TSH, free T4, and T3
Liver function tests	Every 6 months	Reduce dose if 2-5x elevation
Digoxin levels	Every 6-12 months	Monitor for increased serum levels
Prothrombin time/INR	Weekly for first 6 weeks	Monitor for increased anticoagulant effect
Pulmonary function tests	Every 3-6 months	Include DLCO and chest imaging
Ophthalmologic examination	Every 6 months	Check for corneal microdeposits
ECG	Regularly	Monitor for QT prolongation

1

Important Drug Interactions and Precautions

Critical Drug Interactions

• Warfarin: Reduce dose by 30-50%; monitor INR closely
• Digoxin: Reduce dose by approximately 50%; monitor levels
• Statins: Increased risk of myopathy/rhabdomyolysis
• Beta-blockers/calcium channel blockers: Increased risk of bradycardia and heart block
• Other antiarrhythmics: Reduce doses by 30-50%
• Cyclosporine: Monitor levels closely
• Grapefruit juice: Avoid (increases amiodarone levels by 50%)

Major Toxicities to Monitor

1. Pulmonary toxicity: Interstitial pneumonitis (potentially fatal)
2. Thyroid dysfunction: Both hypothyroidism (2-10%) and hyperthyroidism (2%)
3. Hepatotoxicity: Monitor for hepatocellular injury
4. Cardiac: QT prolongation, bradycardia, heart block
5. Neurologic: Tremor, ataxia, peripheral neuropathy
6. Ophthalmologic: Corneal microdeposits (nearly universal), optic neuropathy
7. Dermatologic: Photosensitivity, blue-gray skin discoloration

Special Considerations

• Amiodarone has a very long half-life (40-55 days) due to extensive tissue distribution
• Effects and toxicities may persist for weeks to months after discontinuation
• Use lowest effective maintenance dose (often 200 mg/day) to minimize toxicity 1
• Intravenous amiodarone must be administered via volumetric infusion pump
• Concentrations >2 mg/mL should be administered via central venous catheter 2
• For infusions >2 hours, use glass or polyolefin bottles containing D5W 2

Clinical Pitfalls to Avoid

• Never exceed recommended infusion rates - rapid infusion has caused fatal hepatic necrosis and acute renal failure 2
• Don't overlook drug interactions - amiodarone inhibits multiple CYP450 pathways
• Monitor thyroid function carefully - new arrhythmias may signal hyperthyroidism
• Reduce anticoagulant doses - failure to do so can lead to serious bleeding
• Don't miss early signs of pulmonary toxicity - progressive dyspnea requires prompt evaluation
• Avoid in pregnancy - can cause fetal harm