Intravenous Amiodarone Dosing for Atrial Fibrillation
Standard Loading Protocol
For rate control or rhythm conversion in atrial fibrillation, administer amiodarone as a 150 mg IV bolus over 10 minutes, followed by 1 mg/min 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
Initial Bolus
- Give 150 mg IV over 10 minutes as the loading bolus 1
- This initial dose begins rate control, which typically occurs after the first 300–400 mg 2
Maintenance Infusion
- Early maintenance: 1 mg/min for 6 hours (total 360 mg) 1
- Late maintenance: 0.5 mg/min for 18 hours (total 540 mg) 1
- Total 24-hour dose should not exceed 2.2 g 1
Expected Clinical Response
Rate Control
- Ventricular rate reduction is the most immediate and predictable response 2
- Rate control generally occurs after the first 300–400 mg 2
- In patients with rapid ventricular rates (>135 bpm), heart rate decreases to approximately 104 bpm at 30 minutes and 94 bpm at 60 minutes 3
Rhythm Conversion
- Cardioversion to sinus rhythm occurs in 34–69% with bolus-only regimens and 55–95% with bolus plus continuous infusion 1, 4
- Most conversions occur after 6–8 hours of therapy and often require ≥1000 mg total dose 1, 4
- Conversion rates are 28% at 30 minutes and 42% at 60 minutes with high-dose bolus regimens 3
- Higher doses (>1500 mg/day) are superior to placebo for cardioversion 4
Critical Monitoring Requirements
During Infusion
- Continuous cardiac monitoring throughout the infusion period 1
- Blood pressure monitoring for hypotension (occurs in 16% of patients) 1
- Watch for bradycardia (occurs in 4.9% with IV therapy) and atrioventricular block 1
- Monitor QT interval for excessive prolongation 1
Common Pitfalls
- Asymptomatic hypotension may occur, particularly with bolus dosing 3
- Symptomatic bradycardia requiring intervention occurs in approximately 4% of patients 5
- Superficial phlebitis at the infusion site can develop; consider central access for prolonged infusions 3
Special Clinical Considerations
Structural Heart Disease
- Amiodarone is the preferred agent in patients with heart failure or reduced ejection fraction, where class IC drugs are contraindicated 1, 4
- It is relatively safe in patients with left ventricular dysfunction 4
Renal Impairment
- No dose adjustment needed for renal dysfunction, as amiodarone undergoes hepatic metabolism, not renal excretion 1
Contraindications
- Amiodarone is relatively contraindicated in patients with significant lung disease; if no alternative exists, use the lowest effective dose and shortest duration possible 1
Drug Interactions Requiring Immediate Attention
- Warfarin: Reduce dose by 30–50% and check INR within 3–5 days, as amiodarone significantly increases INR 6, 1
- Digoxin: Reduce dose by 50% immediately, as amiodarone doubles digoxin levels 6, 1
- Statins: Dose adjustments necessary due to cytochrome P450 inhibition 1
- Avoid coadministration with other QT-prolonging medications without expert consultation 1, 7
Transition to Oral Therapy
When to Begin Oral Loading
- Start oral amiodarone at 600–800 mg daily in divided doses while continuing the IV infusion at 0.5 mg/min after approximately 8 hours of IV therapy 6
- Continue oral loading until a cumulative dose of approximately 10 g is reached (typically 1–2 weeks) 6, 1