What is the loading dose of amiodarone (antiarrhythmic medication) for treating atrial fibrillation (A.Fib)?

Amiodarone Loading Dose for Atrial Fibrillation

For intravenous amiodarone in atrial fibrillation, administer 150 mg over 10 minutes as the initial loading dose, followed by 1 mg/min for 6 hours, then 0.5 mg/min thereafter, delivering approximately 1000 mg over the first 24 hours. 1, 2

Intravenous Loading Regimen (Preferred for Acute Management)

The FDA-approved and guideline-recommended IV loading protocol consists of: 1, 2

• Initial bolus: 150 mg in 100 mL D5W infused over 10 minutes 1, 2
• Followed by: 1 mg/min continuous infusion for 6 hours (360 mg) 1, 2
• Maintenance: 0.5 mg/min thereafter (720 mg per 24 hours) 1, 2
• Total first 24 hours: Approximately 1000 mg 1, 2

Alternative Higher-Dose IV Regimen

The European Society of Cardiology guidelines describe an alternative loading approach: 1

• Initial dose: 5-7 mg/kg over 1-2 hours 1
• Followed by: 50 mg/hour to a maximum of 1.0 g over 24 hours 1

Breakthrough Episodes

For recurrent VF or hemodynamically unstable VT during treatment, repeat the 150 mg bolus over 10 minutes. 1, 2

Oral Loading Regimen (Outpatient or Non-Urgent)

When oral loading is appropriate, two established regimens exist: 1

• Standard regimen: 600-800 mg daily in divided doses for 4 weeks, then 200 mg daily maintenance 1
• Rapid loading: 1000 mg (1 g) daily for 1 week, then lower maintenance doses 1
• Alternative: 600 mg daily for 1 week, then 400 mg daily for 3 weeks 3

The total loading dose typically reaches 6-10 g administered over 2-4 weeks before transitioning to maintenance therapy. 1

Critical Administration Requirements

Infusion Preparation and Delivery

• Use a volumetric infusion pump—drop counter sets can underdose by up to 30% due to altered surface properties 2
• Administer through a central venous catheter whenever possible 1, 2
• Use an in-line filter during administration 2
• For concentrations >2 mg/mL, a central line is mandatory 1, 2
• Concentrations >3 mg/mL cause high rates of peripheral vein phlebitis 2
• Administer in glass or polyolefin bottles containing D5W for infusions >2 hours 2

Maximum Rate Warning

Never exceed an initial infusion rate of 30 mg/min—faster rates have resulted in hepatocellular necrosis, acute renal failure, and death. 2

Expected Time to Conversion

Amiodarone has a delayed onset compared to other antiarrhythmics: 1

• Most conversions occur 8-12 hours after initiation 1
• IV regimens achieve 55-95% conversion rates depending on dose 4
• Higher doses (>1500 mg/24h) are superior to placebo 4
• Oral loading achieves >85% conversion with single high-dose regimens 4

Predictors of Successful Cardioversion

Three factors predict conversion success: 4

• Shorter duration of atrial fibrillation 4
• Smaller left atrial size 4, 3
• Higher amiodarone dose 4

Chronic AF >1 year duration has lower success (57%) but still reasonable conversion rates. 5

Monitoring During Loading

Immediate Monitoring

• Continuous ECG monitoring for QT prolongation and bradycardia 1
• Blood pressure monitoring for hypotension (most common adverse effect) 1
• Heart rate assessment for excessive bradycardia or AV block 1, 2

Management of Hypotension

If hypotension develops during IV loading: 1, 2

• Slow the infusion rate as first-line intervention 1, 2
• Add vasopressor drugs if needed 1
• Consider positive inotropic agents 1
• Provide volume expansion 1

Bradycardia Management

For significant bradycardia or AV block: 1, 2

• Slow or discontinue the infusion 1, 2
• Have IV atropine or isoproterenol available 1
• Ensure temporary transcutaneous pacing capability 1

Drug Interaction Considerations During Loading

Rate-Control Medication Adjustments

Reduce doses of other rate-controlling medications when initiating amiodarone, and stop them if heart rate slows excessively. 1, 6

Anticoagulation Interactions

• Reduce warfarin dose in anticipation of INR increases 1
• Amiodarone inhibits warfarin metabolism, causing significant INR elevation 1

Digoxin Interactions

• Reduce digoxin dose upon amiodarone initiation 1
• Serum digoxin levels typically rise with concurrent amiodarone 1

Patient-Specific Considerations

Structural Heart Disease

Amiodarone is particularly advantageous in patients with: 4, 7

• Structural heart disease 4
• Left ventricular systolic dysfunction 4, 7
• Heart failure 7

These patients cannot safely receive Class IC agents (flecainide, propafenone), making amiodarone the preferred option. 4

Hemodynamic Instability

For severely hemodynamically compromised patients, electrical cardioversion remains the method of choice over pharmacological approaches. 1

Common Pitfalls to Avoid

• Do not use drop counter infusion sets—they underdose by up to 30% 2
• Do not exceed 2 mg/mL concentration without central access 2
• Do not use evacuated glass containers for admixing—buffer incompatibility causes precipitation 2
• Do not initiate beta-blockers concurrently during loading without careful rate monitoring 6
• Do not continue full doses of digoxin or warfarin without dose reduction 1

Maintenance After Loading

Continue maintenance infusion at 0.5 mg/min (720 mg/24h) for up to 2-3 weeks regardless of age, renal function, or left ventricular function. 2 Transition to oral maintenance dosing of 100-200 mg daily when clinically appropriate. 1