What is the recommended intravenous amiodarone dosing regimen, monitoring parameters, and contraindications for rapid control of ventricular tachycardia, ventricular fibrillation, or refractory atrial fibrillation when oral therapy is not feasible?

Intravenous Amiodarone Infusion Protocol

For life-threatening ventricular arrhythmias (VT/VF), administer IV amiodarone as a 150 mg bolus over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours, delivering approximately 1,050 mg over 24 hours. 1, 2

Standard Three-Phase Infusion Regimen

Initial Rapid Loading

• 150 mg IV diluted in 100 mL D5W infused over 10 minutes 1, 2
• For breakthrough VF or hemodynamically unstable VT during infusion, repeat the 150 mg bolus 1, 2

First Maintenance Phase

• 1 mg/min for 6 hours (360 mg total) 1, 2

Second Maintenance Phase

• 0.5 mg/min for remaining 18 hours (540 mg total) 1, 2
• This delivers approximately 1,050 mg total over the first 24 hours 1

Cardiac Arrest Modification

For pulseless VT/VF unresponsive to defibrillation and epinephrine, give 300 mg IV/IO bolus, with a second 150 mg bolus if the rhythm persists. 1

Absolute Contraindications

Do not administer IV amiodarone in patients with: 1, 2

• Second- or third-degree AV block without a functioning pacemaker
• Marked sinus bradycardia or sick sinus syndrome without a pacemaker
• Cardiogenic shock
• Known hypersensitivity to amiodarone or iodine

Critical Monitoring Parameters

Cardiovascular Monitoring

• Hypotension occurs in 16-26% of patients receiving IV amiodarone—slow the infusion rate if blood pressure drops; add vasopressors, inotropes, or volume expansion as needed 1, 3, 4
• Bradycardia and AV block occur in 4.9% of IV patients—slow or discontinue the infusion if heart rate falls below 50 bpm or new heart block develops 1
• QT prolongation is common but rarely causes torsades de pointes—monitor daily ECG for QT >500 ms 1

Continuous Telemetry

• Maintain continuous cardiac monitoring for at least 24 hours after initiating IV amiodarone 5
• Check 12-lead ECG daily to assess QT interval and detect heart block 5

Immediate Drug Interaction Management

Digoxin

Reduce digoxin dose by 50% immediately when starting IV amiodarone, as amiodarone doubles digoxin levels. 5, 1

Warfarin

Reduce warfarin dose by 30-50% and check INR within 3-5 days, as amiodarone significantly increases anticoagulation. 5, 1

Atrial Fibrillation Rate Control

For AF with heart failure or accessory pathway, amiodarone is a Class IIa recommendation: 6

• Loading dose: 150 mg over 10 minutes
• Maintenance: 0.5 to 1 mg/min IV
• Onset of rate control: Days (not immediate) 6

Important caveat: Amiodarone is NOT first-line for AF rate control in hemodynamically stable patients without heart failure—beta blockers, diltiazem, or verapamil are preferred (Class I recommendations with onset in 2-7 minutes). 6

Transition to Oral Therapy

Timing Based on IV Duration

After <1 week of IV amiodarone: 5, 1, 7

• Start oral amiodarone 800-1,600 mg daily in divided doses
• Continue until cumulative 10 g oral load achieved (typically 1-2 weeks)

After 1-3 weeks of IV amiodarone: 5, 1, 7

• Start oral amiodarone 600-800 mg daily in divided doses
• Continue until cumulative 10 g oral load achieved

After >3 weeks of IV amiodarone: 7

• Start oral amiodarone 400 mg daily
• Tissue saturation is already substantial

Overlap Strategy

Begin oral amiodarone while IV infusion continues at 0.5 mg/min, then discontinue IV after 24 hours of oral dosing. 5 This accounts for amiodarone's extremely long half-life (up to 100 days) and ensures adequate tissue saturation during the transition. 5

Maintenance Dosing

After completing the 10 g cumulative oral load, reduce to 200-400 mg daily (some patients require only 100-200 mg daily). 5, 7

Efficacy Expectations

Ventricular Arrhythmias

• 63% response rate for life-threatening VT with high-dose IV amiodarone 4
• Dose-response relationship exists: Higher 24-hour doses (1,000 mg vs 125 mg) significantly reduce arrhythmia event rates and increase time to first event 3
• Important limitation: Amiodarone is poorly effective for acute termination of sustained monomorphic VT (only 29% termination rate within 20 minutes), but effective for suppression and prevention of recurrent episodes 8

Atrial Fibrillation

• Rate control is the most immediate and predictable response, typically after the first 300-400 mg 9
• Cardioversion may occur but often takes 24 hours and ≥1,000 mg total dose 9
• 62% of patients remain in sinus rhythm at 1 year after cardioversion with oral amiodarone maintenance, compared to 23% with Class I agents 5

Common Pitfalls to Avoid

1. Do not use IV calcium channel blockers or digoxin in AF with preexcitation syndrome—they may paradoxically accelerate ventricular response 6

2. Do not use IV calcium channel blockers in decompensated heart failure with AF—they worsen hemodynamics 6

3. Do not expect immediate rhythm conversion—amiodarone's full antiarrhythmic effect takes days to weeks despite adequate serum levels 5, 7

4. Do not forget electrolyte correction—check and correct potassium and magnesium before and during amiodarone therapy, as deficiencies increase proarrhythmic risk 5

5. Hypotension is the most common adverse event (26% incidence)—have vasopressors readily available and slow the infusion rate if blood pressure drops 3