What is the recommended dosing, administration protocol, and monitoring for an intravenous amiodarone infusion in a patient with unstable ventricular tachycardia or ventricular fibrillation without contraindications?

Amiodarone Infusion Protocol for Unstable Ventricular Arrhythmias

Recommended Dosing Regimen

For patients with unstable ventricular tachycardia or ventricular fibrillation, administer an initial loading dose of 150 mg IV over 10 minutes, followed by 1 mg/min for 6 hours, then 0.5 mg/min maintenance infusion, with a maximum total dose of 2.2 g over 24 hours. 1, 2

Loading Phase

• Rapid loading: 150 mg in 100 mL D5W infused over 10 minutes for immediately life-threatening situations 1, 2
• Repeat bolus: For breakthrough episodes of VF or hemodynamically unstable VT, repeat the 150 mg bolus over 10 minutes 1, 2

Maintenance Infusion

• First 6 hours: 1 mg/min (360 mg total) 1, 2
• After 6 hours: 0.5 mg/min for remaining 18 hours (540 mg total) 1, 2
• Total 24-hour dose: Approximately 1000 mg (including loading dose), not to exceed 2.2 g 1, 2

Dose-Response Evidence

The 1000 mg/24-hour regimen demonstrates superior efficacy compared to lower doses, with significantly decreased arrhythmia event rates (0.02 events/hour vs 0.07 events/hour for 125 mg dose), longer time to first arrhythmic event, and fewer required supplemental boluses 3

Administration Protocol

Vascular Access Requirements

Administer through a central venous catheter whenever possible, as peripheral vein phlebitis occurs frequently with concentrations >2 mg/mL. 4

• Use an in-line filter during administration 4
• If peripheral access is necessary initially, transition to central access as soon as feasible 4

Infusion Rate Adjustments

• If hypotension develops (occurs in 16% of patients): Slow the infusion rate immediately and consider vasopressor drugs, positive inotropic agents, or volume expansion 1, 2
• If bradycardia or heart block develops (occurs in 4.9% of patients): Discontinue the infusion or reduce the rate 1, 2

Absolute Contraindications

Amiodarone IV is contraindicated in patients with: 2

• Known hypersensitivity to amiodarone or iodine
• Cardiogenic shock
• Marked sinus bradycardia
• Second- or third-degree AV block unless a functioning pacemaker is in place

Mandatory Monitoring Requirements

Continuous Monitoring During Infusion

Continuous ECG monitoring is mandatory throughout the entire infusion period. 4, 5

Monitor specifically for:

• Heart rate and rhythm 4, 5
• PR interval prolongation 4
• QRS duration widening 4
• QT interval prolongation (though torsades de pointes is rare with amiodarone) 5
• Development of second- or third-degree heart block 4, 5

Hemodynamic Monitoring

• Blood pressure continuously, as hypotension occurs in 16% of patients receiving IV amiodarone 1, 2
• Cardiac output in patients with severe left ventricular dysfunction 6

Laboratory Monitoring

• Baseline liver function tests and thyroid studies before initiating therapy 7
• Monitor liver enzymes if infusion continues beyond 24 hours 7

Critical Management Considerations

Drug Interactions Requiring Immediate Dose Adjustments

If the patient is on warfarin, reduce the warfarin dose by 50% immediately and monitor INR at least weekly for the first 6 weeks, as amiodarone significantly increases anticoagulation effects. 7, 4

If the patient is on digoxin, reduce the digoxin dose by 50% when starting amiodarone, as digoxin levels predictably double. 7, 4

Concomitant Rate-Control Medications

Exercise extreme caution if the patient is already receiving beta-blockers, calcium channel blockers, or digoxin, as these create additive AV nodal suppression effects and substantially increase bradycardia risk 4

High-Risk Populations Requiring Enhanced Vigilance

Patients with Severe Left Ventricular Dysfunction

Two critical considerations in this population:

• Significantly higher risk of hypotension during the loading phase 6
• May require slower infusion rates or lower initial doses 6
• Have vasopressors immediately available 2

Female Patients

Women have higher rates of amiodarone-associated bradycardia requiring permanent pacemaker implantation compared to men 4

Common Pitfalls and How to Avoid Them

Phlebitis Prevention

The most common administration error is infusing concentrated amiodarone through peripheral veins—this causes phlebitis in the majority of patients when concentrations exceed 2 mg/mL 4. Always use central access for prolonged infusions.

Overlooking Congestive Heart Failure

If the patient develops dyspnea or cough during or shortly after amiodarone infusion, exclude congestive heart failure first before attributing symptoms to amiodarone pulmonary toxicity, as heart failure mimics amiodarone pneumonitis. 7

Inadequate Response to Breakthrough Arrhythmias

For recurrent VF or unstable VT during the maintenance infusion, do not simply increase the infusion rate—instead, administer another 150 mg bolus over 10 minutes 1, 2

Transition to Oral Therapy

Due to amiodarone's extremely long half-life (average 58 days, range 15-100 days), there is significant overlap between IV and oral dosing 4. When transitioning:

• Begin oral amiodarone while continuing IV infusion at reduced rate
• Typical oral loading is 400-600 mg daily in divided doses 7
• Target maintenance dose is 200-400 mg daily, using the lowest effective dose to minimize long-term toxicity 7

Expected Clinical Outcomes

With the recommended 1000 mg/24-hour regimen, 78% of patients with life-threatening ventricular arrhythmias survive to at least 48 hours 3. The median time to arrhythmia suppression is dose-dependent, with higher doses producing faster and more sustained control 3.