What is the appropriate amiodarone dosing regimen for an adult with ventricular tachycardia that persists despite repeated electrical shocks?

Amiodarone Dosing for Shock-Refractory Ventricular Tachycardia

For shock-refractory ventricular tachycardia, administer amiodarone 300 mg (5 mg/kg) IV over 10-15 minutes, followed by a maintenance infusion of 1 mg/min for 6 hours, then 0.5 mg/min thereafter, with a maximum of 2.2 g in the first 24 hours. 1, 2, 3

Initial Bolus Dosing

The FDA-approved regimen for life-threatening ventricular arrhythmias begins with 150 mg IV over 10 minutes, which can be repeated for recurrent episodes. 1, 3 However, for cardiac arrest situations or immediately life-threatening shock-refractory VT, the evidence supports a more aggressive approach: 300 mg (5 mg/kg) administered over 10-15 minutes. 2, 4 This higher initial dose may be repeated after one hour if breakthrough arrhythmias occur. 2

• The 2010 AHA guidelines specifically recommend 150 mg over 10 minutes for stable patients, with supplemental 150 mg boluses available for recurrent arrhythmias (limited to 6-8 supplemental boluses per 24 hours). 1
• The more recent consensus from multiple guidelines supports the 300 mg loading dose for cardiac arrest scenarios, which shock-refractory VT clinically resembles. 2, 4

Maintenance Infusion Protocol

After the initial bolus, immediately begin a two-phase maintenance infusion: 1, 2, 3

• Phase 1: 1 mg/min for 6 hours (total 360 mg)
• Phase 2: 0.5 mg/min for the remaining 18 hours (total 540 mg)

This delivers approximately 1,000 mg over the first 24 hours when combined with the initial bolus. 2, 4

Maximum Dosing Limits

The absolute maximum dose is 2.2 g in the first 24 hours. 1, 2, 3 This ceiling exists because higher doses significantly increase the risk of hypotension and bradycardia without improving efficacy. 1

Administration Requirements

Dilution and Concentration

• Amiodarone must be diluted in 5% dextrose in water (D5W) only—normal saline causes precipitation. 4
• Concentration should not exceed 2 mg/mL unless administered through a central venous catheter, as peripheral administration causes phlebitis at higher concentrations. 4, 3
• Use an in-line filter during administration. 4

Route of Administration

• Central venous access is strongly preferred to avoid phlebitis and ensure reliable delivery during hemodynamic instability. 4

Critical Monitoring During Administration

Continuous monitoring is mandatory throughout the infusion: 2, 4

• ECG monitoring: Watch for bradycardia, AV block (second or third degree), QT prolongation, and changes in QRS duration
• Blood pressure: Hypotension occurs in 16% of patients receiving IV amiodarone 4
• Heart rate: Drug-related bradycardia occurs in 4.9% of patients 4

Management of Adverse Effects

If hypotension develops: 2, 3

• Slow or temporarily stop the infusion
• Add vasopressor support if needed
• Consider volume expansion

If bradycardia or heart block develops: 4, 3

• Immediately reduce infusion rate or discontinue
• Prepare for temporary pacing if second or third-degree AV block occurs

Relative Contraindications Requiring Extreme Caution

Amiodarone should be used with extreme caution or avoided in: 4, 3

• Baseline heart rate <60 bpm (use only if immediately life-threatening and no alternatives exist)
• Systolic blood pressure <100 mmHg
• Moderate to severe left ventricular dysfunction
• Second or third-degree AV block without a functioning pacemaker (absolute contraindication)

Evidence Quality and Clinical Context

The recommendation for 300 mg loading dose in shock-refractory VT is based on extrapolation from cardiac arrest protocols, where this dosing has become standard practice. 2, 4 The original FDA approval used 150 mg dosing 3, but clinical practice has evolved based on the recognition that shock-refractory VT represents a near-arrest state requiring more aggressive initial therapy.

Important caveat: Research evidence suggests IV amiodarone has limited acute efficacy for terminating sustained monomorphic VT, with termination rates of only 29% in one study. 5 However, it remains guideline-recommended because it reduces the frequency of recurrent episodes and stabilizes the rhythm even when it doesn't immediately terminate the arrhythmia. 1, 6 The 40% response rate in the multicenter trial supports its use as a temporizing measure while preparing for definitive therapy (such as catheter ablation or ICD placement). 6

Drug Interactions Requiring Dose Adjustments

Before administering amiodarone, adjust these medications: 2, 4

• Digoxin: Reduce dose by 50% (levels predictably double)
• Warfarin: Reduce dose by one-third to one-half and monitor INR at least weekly
• Other QT-prolonging drugs: Avoid without specialist consultation