What are the indications, dosing regimen, and contraindications for intravenous amiodarone infusion?

Amiodarone Intravenous Infusion: Indications, Dosing, and Contraindications

Primary Indications

Intravenous amiodarone is indicated for initiation of treatment and prophylaxis of frequently recurring ventricular fibrillation (VF) and hemodynamically unstable ventricular tachycardia (VT) in patients refractory to other therapy. 1

Additional clinical scenarios where IV amiodarone may be used include:

• Cardiac arrest with VF/pulseless VT: Administer 300 mg IV/IO bolus over 10 minutes when the rhythm is unresponsive to defibrillation and epinephrine, with a second 150 mg bolus if the arrhythmia persists 2
• Hemodynamically stable wide-complex tachycardia: IV amiodarone is appropriate for stable monomorphic VT, though the delayed onset of action (20-30 minutes with most conversions occurring after 6-8 hours) makes it less suitable as a first-line agent unless the patient remains clinically stable 3
• Atrial fibrillation with heart failure: IV amiodarone may be used for rate control in AF patients with heart failure when other measures (beta-blockers, calcium channel blockers, digoxin) are unsuccessful or contraindicated (Class IIa recommendation) 3
• Supraventricular tachycardia in pregnancy: IV amiodarone may be considered for acute treatment in pregnant patients with potentially life-threatening SVT when other therapies are ineffective or contraindicated, though fetal hypothyroidism occurs in approximately 17% of cases 4

Standard Dosing Regimen

For Life-Threatening Ventricular Arrhythmias

The FDA-approved regimen delivers approximately 1000 mg over the first 24 hours: 1

• Rapid loading dose: 150 mg diluted in 100 mL D5W infused over 10 minutes 3, 1
• Early maintenance infusion: 1 mg/min for 6 hours (≈360 mg total) 3, 1
• Late maintenance infusion: 0.5 mg/min for the remaining 18 hours (≈540 mg total) 3, 1
• Maximum daily dose: Do not exceed 2.2 g of amiodarone within any 24-hour period 3, 2

For Breakthrough Arrhythmias

• Supplemental boluses: For recurrent VF or hemodynamically unstable VT, repeat the 150 mg loading dose over 10 minutes 1
• Maximum supplemental boluses: Up to 6-8 additional 150 mg boluses (each diluted in 100 mL D5W over 10 minutes) may be given within 24 hours in patients with refractory arrhythmias 2

Administration Requirements

• Concentration limits: Do not exceed 2 mg/mL concentration for peripheral infusions; concentrations >2 mg/mL require a central venous catheter to prevent severe phlebitis 3, 2
• Diluent: Amiodarone must be diluted with 5% dextrose in water (D5W); normal saline or lactated Ringer's solution will cause precipitation 3
• In-line filter: Use an in-line filter during administration 3

Absolute Contraindications

Amiodarone is absolutely contraindicated in the following situations: 1

• Known hypersensitivity to amiodarone or any of its components, including iodine 1
• Cardiogenic shock 1
• Marked sinus bradycardia 1
• Second- or third-degree AV block unless a functioning pacemaker is in place 3, 2, 1
• Sick sinus syndrome without a pacemaker 2

Relative Contraindications and High-Risk Situations

Use extreme caution or avoid IV amiodarone in these scenarios: 3

• Baseline heart rate <60 bpm: Amiodarone should only be given if the arrhythmia is immediately life-threatening and no alternatives exist, as drug-related bradycardia occurs in 4.9% of IV patients 3
• Systolic blood pressure <100 mmHg: Hypotension occurs in 16-26% of patients receiving IV amiodarone 3, 5
• Moderate or severe left ventricular dysfunction: Patients with severely impaired LV function are at higher risk for hemodynamic compromise 3, 6
• Hepatic dysfunction: Use with extreme caution 2
• Acute inflammatory lung disease: Contraindicated 2

Critical Monitoring Requirements

Continuous monitoring is mandatory during IV amiodarone administration: 3, 2

• Cardiac rhythm and heart rate: Monitor continuously for bradycardia, AV block, and arrhythmia recurrence 3
• Blood pressure: Hypotension is the most common adverse event (16-26% incidence); slow the infusion rate and add vasopressors, positive inotropic agents, or volume expansion as needed 3, 1, 5
• ECG parameters: Monitor PR interval, QRS duration, and QT interval; QT prolongation >500 ms warrants dose adjustment 7, 3
• Defibrillator availability: A defibrillator must be immediately available during administration 2

Critical Drug Interactions

Amiodarone has significant interactions requiring immediate dose adjustments: 2

• Digoxin: Reduce digoxin dose by 50% immediately when starting amiodarone, as levels will double 7, 2
• Warfarin: Reduce warfarin dose by 30-50% and monitor INR at least weekly (interaction peaks at 7 weeks) 7, 2
• QT-prolonging drugs: Avoid concomitant use without expert consultation 2
• Beta-blockers and calcium channel blockers: These create additive AV nodal suppression and increase bradycardia risk 3

Common Pitfalls and Caveats

• Delayed onset of action: The antiarrhythmic effect typically becomes apparent 20-30 minutes after administration, with most conversions occurring after 6-8 hours and often requiring ≥1 g total dose; this makes amiodarone inappropriate as first-line therapy unless the patient is hemodynamically stable 3
• Hypotension management: If hypotension develops, slow the infusion rate rather than discontinuing; add vasopressors if needed 1, 5
• Bradycardia or heart block: If these develop, discontinue the infusion or reduce the rate immediately 3
• Gender-specific risk: Women are at higher risk for amiodarone-associated bradycardia requiring permanent pacemaker implantation 7
• Grapefruit interaction: Patients must not consume grapefruit or grapefruit juice during therapy, as it inhibits CYP3A-mediated metabolism and increases plasma levels 3

Alternative Agents When Amiodarone Is Contraindicated

• Procainamide: For stable monomorphic VT, infuse at 20-50 mg/min until arrhythmia suppression, hypotension, ≥50% QRS prolongation, or cumulative dose of 17 mg/kg 3
• Lidocaine: Alternative when amiodarone is unavailable; give initial IV dose of 1-1.5 mg/kg 3
• Electrical cardioversion: Prioritize immediate cardioversion if the patient becomes hemodynamically unstable at any point during pharmacologic therapy 3