What is the typical dose of Amiodarone (antiarrhythmic medication) for treating arrhythmias?

Amiodarone Dosing for Arrhythmias

For life-threatening ventricular arrhythmias requiring IV therapy, administer a 150 mg bolus over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours before transitioning to oral dosing. 1

Intravenous Dosing for Acute/Life-Threatening Arrhythmias

Life-threatening ventricular tachyarrhythmias:

• Initial bolus: 150 mg IV over 10 minutes (may repeat in 10-30 minutes if necessary) 1
• Maintenance infusion: 1 mg/min for 6 hours 1
• Reduced infusion: 0.5 mg/min for 18 hours 1
• Critical administration detail: Use a central venous catheter whenever possible, as peripheral vein phlebitis occurs frequently with concentrations >2 mg/mL 2

Key monitoring during IV administration:

• Continuous ECG monitoring is mandatory for heart rate, AV conduction abnormalities, and QT prolongation 2
• Hypotension occurs in 16% of patients and bradycardia in 4.9% 2
• If bradycardia or heart block develops, discontinue or reduce the infusion rate immediately 2

Oral Loading Dose Regimens

The oral loading strategy differs significantly based on the arrhythmia type and clinical urgency:

For ventricular arrhythmias (inpatient):

• Loading: 800-1,600 mg/day in divided doses until a total of 10 grams has been administered 1
• Maintenance: 200-400 mg/day 1
• Alternative approach: 50 mg/kg/day for 3 days, then 30 mg/kg/day for 2 days, followed by 300-400 mg twice daily 3

For atrial fibrillation:

• Loading: 600-800 mg/day in divided doses until a total of 10 grams has been given 1
• Maintenance: 200 mg/day 1
• Higher initial doses (up to 1,200 mg daily) may be considered in inpatient monitoring settings, though this increases adverse effect risk 4

Standard AHA recommendation:

• Loading: 400-600 mg daily in divided doses for 2-4 weeks 4
• Maintenance: 100-200 mg daily 4

Transitioning from IV to Oral Dosing

The conversion dose depends critically on the duration of IV therapy, as tissue stores accumulate over time:

IV duration <1 week:

• Transition to 800-1,600 mg oral amiodarone per day 1, 4

IV duration 1-3 weeks:

• Transition to 600-800 mg oral amiodarone per day 1, 4

IV duration >3 weeks:

• Transition to 400 mg oral amiodarone per day 1, 4

The rationale: Patients on IV amiodarone for 1-3 weeks have already accumulated significant tissue stores, so lower oral doses suffice to maintain therapeutic levels 4

Critical Dosing Considerations

Dose reduction is essential for long-term therapy:

• Virtually all patients develop side effects at maintenance doses of 600 mg/day 5
• The dose should be kept at the lowest effective level to minimize toxicity 2
• In one study, doses were reduced from 572±283 mg/day at 45 days to 372±174 mg/day at 6 months due to frequent side effects 5

Pharmacokinetic factors affecting dosing:

• Amiodarone has an extremely long half-life averaging 58 days (range 15-100 days) 2, 6
• Maximal antiarrhythmic effects are not attained before 90-150 days of treatment 6
• Antiarrhythmic protection may persist for up to 150 days or more after discontinuation 6
• The onset of IV amiodarone's antiarrhythmic effect occurs in less than 30 minutes 1

Common Pitfalls and Contraindications

Absolute contraindications to IV amiodarone:

• Bradycardia or second/third-degree heart block without a pacemaker 2
• Baseline heart rate of 57 bpm represents relative contraindication unless the patient has a pacemaker or the situation is immediately life-threatening 2

Mandatory drug interaction adjustments:

• Reduce digoxin dose by 50% when starting amiodarone, as digoxin levels predictably double 2
• Reduce warfarin dose by one-third to one-half and monitor INR at least weekly for the first 6 weeks, as interaction effects don't peak until 7 weeks 2
• Avoid grapefruit or grapefruit juice, as it inhibits CYP3A-mediated metabolism and increases plasma levels 2

Monitoring requirements:

• Monitor liver and thyroid function every 6 months during maintenance therapy 2
• Watch for bradycardia, QT prolongation, hypotension, and heart block during loading 4
• Monitor for pulmonary toxicity, thyroid dysfunction, and hepatic toxicity during long-term therapy 4

Clinical Context for Dosing Decisions

When to use lower maintenance doses:

• Amiodarone should be used as a second-line drug in long-term treatment of atrial fibrillation in patients with structural heart disease 1
• Long-term amiodarone therapy does not appear justified in relatively asymptomatic patients taking anticoagulants if rate-control strategies provide satisfactory symptomatic improvement 1

Efficacy by arrhythmia type:

• Moderate doses (400 mg/day) are highly effective in suppressing "warning" ventricular arrhythmias in chronic ischemic heart disease 6
• Treatment of sustained recurrent VT and malignant arrhythmias requires doses of approximately 800 mg/day 6
• With high-dose loading (800 mg/day for 6 weeks, then 600 mg/day maintenance), 69% of patients with refractory VT/VF had no recurrence over 14 months of follow-up 7