What is the recommended dosing regimen for amiodarone (antiarrhythmic medication) in an inpatient with atrial fibrillation (afib)?

Amiodarone Dosing for Inpatient Atrial Fibrillation

Intravenous Loading and Maintenance Regimen

For inpatient atrial fibrillation requiring acute rhythm or rate control, administer amiodarone as a 150 mg IV bolus over 10 minutes, followed by 1 mg/min infusion for 6 hours (360 mg), then 0.5 mg/min for 18 hours (540 mg), with a maximum total dose of 2.2 g over 24 hours. 1, 2

Initial Loading Phase

• First 10 minutes: 150 mg IV bolus over 10 minutes 1, 2
• Next 6 hours: 1 mg/min continuous infusion (360 mg total) 1, 2
• Following 18 hours: 0.5 mg/min continuous infusion (540 mg total) 1, 2
• Total 24-hour dose: Approximately 1050 mg, not to exceed 2.2 g 1, 2

Administration Requirements

• Use a volumetric infusion pump (not drop counters, which can underdose by up to 30%) 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 to avoid peripheral vein phlebitis 2
• Deliver in glass or polyolefin bottles with D5W for infusions exceeding 2 hours 2

Breakthrough Arrhythmia Management

If breakthrough atrial fibrillation or hemodynamically unstable tachycardia occurs during maintenance infusion:

• Administer supplemental 150 mg IV bolus over 10 minutes 1, 2
• May increase maintenance infusion rate to achieve arrhythmia suppression 2
• Do not exceed initial infusion rate of 30 mg/min 2

Transition to Oral Therapy

When transitioning from IV to oral amiodarone, the conversion dose depends on duration of IV therapy: 3, 4

• After <1 week IV: 800-1600 mg oral daily 3, 4
• After 1-3 weeks IV: 600-800 mg oral daily 3, 4
• After >3 weeks IV: 400 mg oral daily 4

Oral Loading and Maintenance

• Loading phase: 600-800 mg daily in divided doses until 10 g total administered (approximately 2-3 weeks) 1, 3
• Maintenance dose: 200 mg daily 1, 3

Expected Clinical Effects and Timeline

Rate Control vs. Rhythm Control

• Rate control occurs most predictably and rapidly, typically after the first 300-400 mg, reducing ventricular rate from baseline 5, 6
• Cardioversion to sinus rhythm is delayed, typically occurring after 6-8 hours and often requiring ≥1000 mg total dose 7, 8, 5
• Conversion rates: 34-69% with bolus-only regimens; 55-95% with bolus plus continuous infusion 7, 8

Predictors of Successful Conversion

• Shorter duration of atrial fibrillation 8
• Smaller left atrial size 8
• Higher amiodarone dose 8
• Chronic AF >1 year is an adverse predictor (though still 57% success rate) 9

Critical Monitoring Requirements

During IV Administration

• Continuous cardiac monitoring for hypotension (occurs in 16% of patients), bradycardia, and AV block 1, 2
• Blood pressure monitoring throughout infusion 1
• ECG monitoring for QT prolongation and heart block 1, 3
• Monitor for bradycardia (occurs in 4.9% with IV therapy) 4

Long-term Monitoring (Oral Therapy)

• Thyroid function tests 1
• Liver function tests 1
• Pulmonary function tests 1
• Ophthalmologic examinations 1
• ECG monitoring 1

Special Clinical Considerations

Safety in Structural Heart Disease

Amiodarone is particularly valuable in patients with structural heart disease or left ventricular dysfunction, where class IC drugs (flecainide, propafenone) are contraindicated. 7, 8

Dose-Related Adverse Effects

• Mean daily doses >2100 mg are associated with increased hypotension risk 2
• Adverse effects occur in 35-51% of patients, often requiring dose reduction 3
• Low-dose maintenance (200 mg daily) minimizes toxicity while maintaining efficacy 3, 9

Critical Warnings

• Hepatocellular necrosis and acute renal failure have occurred with loading infusions at concentrations and rates exceeding recommendations 2
• Amiodarone has an extremely long half-life (IV: 9-36 days; Oral: 26-107 days), leading to delayed onset of adverse effects 1
• Use the lowest effective dose due to dose-related toxicity 1, 3

Drug Interactions

• Warfarin: Amiodarone reduces clearance; expect sudden INR increases 4
• Digoxin: Levels typically double with coadministration 4
• Caution with other QT-prolonging medications 1
• Multiple cytochrome P450 interactions 1, 4

Clinical Context

While amiodarone is effective for both conversion and maintenance, aggressive rhythm control does not improve outcomes in relatively asymptomatic patients compared to rate control with anticoagulation. 3 Reserve amiodarone for highly symptomatic patients when rate-control strategies are inadequate. 3