What is the recommended dose of intravenous (IV) amiodarone for treating ventricular fibrillation or tachycardia?

IV Amiodarone Dosing for Ventricular Fibrillation/Tachycardia

For life-threatening ventricular arrhythmias (VF/VT), administer IV amiodarone as a 150 mg bolus over 10 minutes, followed by 1 mg/min infusion for 6 hours, then 0.5 mg/min for 18 hours, with a maximum 24-hour dose of 2.2 g. 1, 2

Standard Dosing Protocol

The three-stage approach recommended by the American Heart Association and ACC/AHA guidelines consists of:

• Rapid loading infusion: 150 mg IV over 10 minutes 1, 3
• Early maintenance infusion: 1 mg/min for 6 hours (360 mg total) 1, 2
• Late maintenance infusion: 0.5 mg/min for 18 hours (540 mg total) 1, 2

Supplemental boluses: Additional 150 mg infusions over 10 minutes may be given for breakthrough VF/VT, but total 24-hour dose must not exceed 2.2 g 1, 2

Alternative Dosing Regimens

For patients requiring different approaches:

• Higher loading dose: 300 mg over 15 minutes has been used in life-threatening situations, though associated with increased hypotension risk 1
• Weight-based dosing: 5 mg/kg over 1 hour loading dose, followed by maintenance infusion of 5-25 mcg/kg/min titrated to effect 1, 4
• Older ACC/AHA protocol: 500 mg total over 24 hours given as 150 mg over 10 minutes, then 1 mg/min for 6 hours, then 0.5 mg/min 1

Efficacy and Onset

Antiarrhythmic effects begin within 30 minutes of administration 5, with median time to arrhythmia control of 24 hours (range 1-96 hours) in infants with life-threatening tachycardias 4. In dose-ranging studies, higher doses (1000 mg/24h) showed significantly better outcomes than lower doses (125 mg/24h), with median event rates of 0.02 vs 0.07 episodes per hour respectively 6.

Critical Monitoring Requirements

Continuous ECG monitoring is mandatory during all IV amiodarone administration 3, 5:

• Monitor for hypotension (occurs in 16-26% of patients) 2, 6
• Watch for bradycardia (4.9% incidence) and AV block 3, 2
• Reduce infusion rate if heart rate decreases by 10 beats per minute 1, 3
• Monitor blood pressure continuously, especially during loading dose 5

Administration Technique

Use a central venous catheter whenever possible, as peripheral vein phlebitis occurs frequently with concentrations >2 mg/mL 3, 5. An in-line filter should be used during administration 3.

Contraindications and Precautions

Absolute contraindications:

• Second- or third-degree heart block without pacemaker 3, 2
• Severe bradycardia without pacemaker 3

Relative contraindications requiring extreme caution:

• Heart rate <60 bpm (especially <57 bpm) without pacemaker 3
• Systolic blood pressure <100 mmHg 1
• Moderate to severe left ventricular failure 1

Transition to Oral Therapy

When transitioning from IV to oral amiodarone after successful acute management 7:

• If IV therapy <1 week: 800-1,600 mg/day oral in divided doses 7
• If IV therapy 1-3 weeks: 600-800 mg/day oral 7
• If IV therapy >3 weeks: 400 mg/day oral 7

Continue loading until cumulative dose of 10 g is achieved, then reduce to maintenance dose of 200-400 mg daily 7.

Drug Interactions During Acute Use

Critical dose adjustments required:

• Reduce warfarin dose by 50% and monitor INR weekly 3, 7
• Reduce digoxin dose by 30-50% as levels will double 1, 7
• Avoid combining with other QT-prolonging drugs without expert consultation 5
• Grapefruit juice is absolutely contraindicated as it increases amiodarone levels by 50-84% 2

Common Pitfalls to Avoid

Do not administer too rapidly - hypotension is dose-rate dependent and occurs more frequently with rapid boluses >150 mg over <10 minutes 1, 2. The vasoactive solvents in older formulations contributed to hypotension, though newer formulations have reduced this risk 1.

Do not use in polymorphic VT with prolonged QT - amiodarone further prolongs QT interval and may worsen torsades de pointes 1.

Do not stop beta-blockers or other rate-control agents abruptly when starting amiodarone, as this creates risk of rebound ischemia and arrhythmias 5.

Malaysian Context

While specific Malaysian guidelines were not provided in the evidence, the American Heart Association and ACC/AHA protocols described above represent international standard of care and are widely adopted globally 1. The dosing regimen of 150 mg over 10 minutes followed by 1 mg/min for 6 hours, then 0.5 mg/min represents the most evidence-based approach for acute ventricular arrhythmias 1, 2, 6.