What is the dosing regimen for amiodarone (antiarrhythmic medication) in treating atrial fibrillation?

Amiodarone Dosing for Atrial Fibrillation

For atrial fibrillation, use oral amiodarone with a loading dose of 600-800 mg daily in divided doses until 10 grams total is administered, followed by a maintenance dose of 200 mg daily; for acute situations requiring rapid control, give 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. 1, 2

Oral Dosing Regimen (Outpatient/Non-Acute)

Loading Phase:

• Administer 600-800 mg daily in divided doses until a cumulative total of 10 grams has been given 3, 1
• Alternative structured loading: 800 mg daily for 1 week, then 600 mg daily for 1 week, then 400 mg daily for 4-6 weeks 1
• Onset of action occurs within 1-3 weeks with oral administration 1

Maintenance Phase:

• Standard maintenance dose is 200 mg daily 3, 1
• Some patients may require 200-400 mg daily depending on response 3
• The lowest effective dose should be used to minimize adverse effects 1

Intravenous Dosing Regimen (Acute/Inpatient)

For patients requiring rapid rhythm control:

• Initial bolus: 150 mg IV over 10 minutes 1, 2
• Maintenance infusion: 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours 1, 2
• Total first 24-hour dose approximately 1000 mg 2
• Onset of action occurs within days with IV administration 1

For breakthrough arrhythmias during IV therapy:

• Give supplemental 150 mg IV bolus over 10 minutes 2
• May increase maintenance infusion rate cautiously 2

Critical administration details:

• Use concentrations ≤2 mg/mL for peripheral IV to avoid phlebitis 2
• Concentrations >2 mg/mL require central venous catheter 2
• Must use volumetric infusion pump, not drop counters (which can underdose by 30%) 2
• Administer through dedicated central line with in-line filter when possible 2

Transitioning from IV to Oral Therapy

The conversion dose depends on duration of IV therapy:

• After <1 week IV: 800-1600 mg oral daily 1, 4
• After 1-3 weeks IV: 600-800 mg oral daily 1, 4
• After >3 weeks IV: 400 mg oral daily 1
• Continue oral loading until 10 grams total administered, then switch to 200-400 mg daily maintenance 1, 4

Efficacy Considerations

Conversion rates and timing:

• Oral single-dose loading (25-30 mg/kg) achieves >85% conversion at 24 hours 5
• IV high-dose regimens (125 mg/hour up to 3 grams) achieve >90% conversion 5
• Most conversions occur 6-8 hours after therapy initiation 5
• Long-term maintenance of sinus rhythm achieved in 53-79% of patients 6, 7

Predictors of success:

• Shorter duration of atrial fibrillation predicts better outcomes 5
• Chronic AF >1 year has lower success (57%) but still reasonable 6
• Smaller left atrial size favors conversion 5
• Higher amiodarone doses improve conversion rates 5

Adverse Effects and Monitoring

Common adverse effects (occur in 35-51% of patients):

• Bradycardia and AV block (1-3% oral, 4.9% IV) 1, 4
• Hypotension (16% with IV) 4
• QT prolongation (common but torsades de pointes is rare) 3, 1
• GI upset, nausea, constipation 3, 1
• Tremor or ataxia (35%) 8
• Visual halos or blurring (6%) 8

Serious long-term toxicity:

• Pulmonary interstitial infiltrates (5%) 8
• Thyroid dysfunction (6%) 8
• Hepatotoxicity 2
• Adverse effects necessitate dose reduction in 41% and discontinuation in 10% of patients 8

Required monitoring:

• ECG for QT prolongation, bradycardia, and heart block 1
• Thyroid function tests regularly 1
• Liver function tests regularly 1
• Pulmonary function monitoring 1
• Blood pressure during IV administration 1
• Close surveillance especially during first week 4

Critical Safety Warnings

Avoid excessive loading rates:

• IV loading infusions at concentrations and rates exceeding recommendations have caused hepatocellular necrosis and acute renal failure leading to death 2
• Initial infusion rate should not exceed 30 mg/min 2
• Mean daily doses >2100 mg associated with increased hypotension risk 2

Drug interactions requiring dose adjustments:

• Warfarin: reduces clearance, causing sudden INR increases—monitor closely 4
• Digoxin: levels typically double with amiodarone—adjust digoxin dose 4

Special Clinical Situations

When to use amiodarone for AF:

• Reserve for highly symptomatic patients when rate-control strategies with anticoagulation are inadequate 1
• Particularly appropriate in patients with structural heart disease or left ventricular dysfunction where class IC drugs (flecainide, propafenone) are contraindicated 5
• Aggressive rhythm control does not improve outcomes in relatively asymptomatic patients 1

Managing bradycardia on amiodarone:

• Reduce dose to 200 mg every 24 hours rather than discontinuing 1
• Low-dose amiodarone (≤200 mg daily) is effective with fewer side effects 1
• If bradycardia persists despite dose reduction, consider adding other agents 1