What are the loading and maintenance doses of amiodarone (Amiodarone) for atrial fibrillation (A.Fib) with rapid ventricular response (RVR)?

Amiodarone Dosing for Atrial Fibrillation with RVR

For atrial fibrillation with rapid ventricular response, administer IV amiodarone as a 150 mg bolus over 10 minutes, followed by 1 mg/min infusion for 6 hours, then 0.5 mg/min for 18 hours, with a maximum of 2.1 grams in the first 24 hours. 1

Intravenous Loading Regimen

The standard IV loading approach delivers approximately 1000 mg over the first 24 hours: 2

• Initial bolus: 150 mg over 10 minutes 1
• First 6 hours: 1 mg/min continuous infusion (360 mg) 1, 2
• Next 18 hours: 0.5 mg/min continuous infusion (540 mg) 1, 2
• Breakthrough episodes: Additional 150 mg boluses over 10 minutes can be given for recurrent RVR or hemodynamic instability 2

The maintenance infusion rate of 0.5 mg/min (720 mg/24 hours) should continue after the first 24 hours, and can be cautiously maintained for 2-3 weeks. 2 In controlled trials, mean daily doses above 2100 mg were associated with increased hypotension risk. 2

Oral Loading Regimen (When IV Not Required)

If the patient is hemodynamically stable and oral therapy is appropriate: 1, 3

• Loading dose: 600-800 mg daily in divided doses 1, 3
• Duration: Continue until 10 grams total administered (typically 2-4 weeks) 1, 3
• Maintenance: 200 mg daily after loading complete 1, 3

A single oral loading dose of 25-30 mg/kg (approximately 1800-2100 mg for a 70 kg patient) has shown 64% conversion rate within 24 hours in recent-onset atrial fibrillation, though this approach is less commonly used in current practice. 4

Critical Administration Requirements

Amiodarone must be delivered through specific routes to prevent complications: 2

• Use a volumetric infusion pump (not drop counters, which can underdose by 30%) 2
• Administer through a central venous catheter whenever possible 2
• Concentrations >2 mg/mL cause high rates of peripheral vein phlebitis and should only be given via central line 2
• Use an in-line filter during administration 2
• Infusions >2 hours must use glass or polyolefin bottles with D5W (not evacuated glass containers) 2

Mandatory Monitoring During Loading

Continuous surveillance is essential to detect life-threatening complications: 1, 3, 5

• Continuous ECG monitoring for bradycardia, heart block, and QT prolongation 5
• Heart rate checks at weekly intervals minimum during loading phase 3
• Blood pressure monitoring (hypotension occurs in 16% of IV patients) 5
• Baseline and serial thyroid function tests (hypothyroidism risk in elderly) 3
• Liver transaminases at baseline and during loading 3
• If bradycardia or heart block develops, immediately discontinue or reduce infusion rate 5

Critical Drug Interactions Requiring Dose Adjustments

Before starting amiodarone, adjust these medications to prevent toxicity: 3, 5

• Digoxin: Reduce dose by 50% (levels predictably double) 3, 5
• Warfarin: Reduce dose and monitor INR at least weekly for first 6 weeks (peak interaction at 7 weeks) 3, 5
• Rate-controlling medications: Reduce or discontinue beta-blockers and calcium channel blockers as amiodarone takes effect to prevent excessive bradycardia 3
• Grapefruit juice: Must be completely avoided (inhibits metabolism) 3, 5

Absolute Contraindications

Do not administer amiodarone in these situations: 5

• Severe bradycardia or heart rate <60 bpm without pacemaker 5
• Second- or third-degree heart block without pacemaker 5
• Severe hepatic dysfunction 3
• Baseline QT prolongation with history of torsades de pointes 1

When to Choose IV vs. Oral Loading

IV amiodarone is indicated when: 1

• RVR does not respond to other pharmacological therapies 1
• Hemodynamic instability is present 1
• Rapid rate control is needed 6

Oral loading is appropriate when: 1, 3

• Patient is hemodynamically stable 1
• Gradual rate control is acceptable 3
• Long-term rhythm control is the primary goal 1

Expected Time to Effect

Amiodarone has delayed onset compared to other agents: 1, 6

• IV administration: Mean conversion time 171 minutes (approximately 3 hours) in recent-onset AF 6
• Oral loading: Inferior to Class IC drugs at 1-2 hours, but equivalent at 24 hours 1
• Full antiarrhythmic effect: May take days to weeks despite adequate serum levels 7

Common Pitfalls to Avoid

Loading infusions at concentrations and rates exceeding recommendations have resulted in hepatocellular necrosis, acute renal failure, and death. 2, 8 A case report documented acute multi-organ toxicity (hepatotoxicity, AKI, pulmonary distress) within 24 hours of standard IV dosing, which resolved rapidly after discontinuation. 8

Never use drop counter infusion sets - they reduce drop size and can underdose by 30%. 2

Do not initiate dofetilide out of hospital if considering alternative agents for cardioversion. 1