For acute ventricular tachycardia, should amiodarone be given as a 150 mg intravenous bolus over 10 minutes or as 300 mg infused over 1 hour?

Amiodarone Dosing for Acute Ventricular Tachycardia

For hemodynamically stable ventricular tachycardia, administer 150 mg IV over 10 minutes followed by 1 mg/min for 6 hours, then 0.5 mg/min for 18 hours; the 300 mg over 1 hour regimen is reserved only for cardiac arrest with VF/pulseless VT unresponsive to defibrillation. 1, 2, 3

Standard Protocol for Stable Monomorphic VT

The FDA-approved and guideline-recommended regimen consists of:

• Initial bolus: 150 mg IV diluted in 100 mL D5W infused over 10 minutes 1, 2, 3
• Early maintenance: 1 mg/min continuous infusion for 6 hours (≈360 mg total) 1, 2, 3
• Late maintenance: 0.5 mg/min for the subsequent 18 hours (≈540 mg total) 1, 2, 3
• Total first 24 hours: Approximately 1,050 mg, not exceeding 2.2 g maximum 2, 3

This protocol applies to all adult patients regardless of body weight. 4

When to Use the 300 mg Cardiac Arrest Dose

The 300 mg IV bolus over 10 minutes is indicated exclusively for:

• Cardiac arrest with ventricular fibrillation or pulseless VT that remains refractory after defibrillation and epinephrine 2
• A second 150 mg bolus may follow if the arrest rhythm persists 2

This higher dose is not the standard for hemodynamically stable VT. 2

Critical Timing and Efficacy Considerations

Amiodarone has a delayed onset of action that influences dosing strategy:

• The antiarrhythmic effect typically becomes apparent 20–30 minutes after administration 2
• Most conversions to sinus rhythm occur after 6–8 hours of therapy and usually require a cumulative dose of at least 1 g 2
• In one retrospective series, the acute termination rate for stable monomorphic VT was only 29% (8 of 28 patients) when using 150 mg over 10 minutes 5

This delayed onset makes the 150 mg/10 min bolus followed by continuous infusion the appropriate choice for stable VT, as the maintenance infusion provides sustained drug delivery while awaiting therapeutic effect. 2, 5

Breakthrough Arrhythmia Management

If VT recurs during the maintenance infusion:

• Administer supplemental 150 mg boluses (diluted in 100 mL D5W over 10 minutes) 2, 3
• Up to 6–8 additional boluses may be given within 24 hours 2
• Each supplemental bolus counts toward the 2.2 g maximum daily dose 2, 3

Administration Requirements to Prevent Complications

Concentration and access:

• Keep concentration ≤2 mg/mL for peripheral IV access 2, 3
• Concentrations >2 mg/mL require a central venous catheter to prevent severe phlebitis 2, 3
• Use only 5% dextrose in water (D5W) as diluent; normal saline causes precipitation 2, 3

Delivery system:

• Use a volumetric infusion pump; drop-counter sets can underdose by up to 30% 3
• Place an in-line filter in the infusion line 2, 3
• Do not exceed an initial infusion rate of 30 mg/min 3

Hemodynamic Monitoring

Hypotension is the most common adverse effect:

• Occurs in 16–26% of patients receiving IV amiodarone 2
• Directly related to infusion rate 2
• If hypotension develops during the bolus, slow or temporarily pause the infusion 2

Bradycardia and conduction effects:

• Bradycardia occurs in 4.9% of patients 2, 4
• Monitor continuously for AV block, QT prolongation, and QRS widening 2
• Amiodarone is absolutely contraindicated in second- or third-degree AV block without a functioning pacemaker 1, 2, 4

When to Abandon Pharmacologic Therapy

Immediate synchronized cardioversion is indicated if the patient becomes hemodynamically unstable at any point:

• Symptomatic hypotension (systolic BP <90 mm Hg) 1
• Pulmonary edema 1
• Ongoing myocardial ischemia or angina 1
• Altered mental status or syncope 2

Electrical therapy takes priority over continued drug infusion in unstable patients. 1, 2

Common Pitfall: Confusing Stable VT with Cardiac Arrest Protocols

The 300 mg dose is not interchangeable with the 150 mg dose for stable VT. The 300 mg bolus was studied specifically in cardiac arrest scenarios where immediate high-dose loading is justified by the life-threatening nature of pulseless rhythms. 2 For hemodynamically stable monomorphic VT, the 150 mg bolus followed by continuous infusion allows for adequate loading while minimizing hypotension risk and providing sustained therapeutic levels as the drug's antiarrhythmic effect develops over hours. 1, 2, 3

Alternative Agents When Amiodarone Is Inappropriate

If amiodarone is contraindicated or the patient has baseline bradycardia (HR <60 bpm):

• Procainamide: 20–50 mg/min IV until arrhythmia suppression, hypotension, ≥50% QRS prolongation, or 17 mg/kg cumulative dose 1, 2
• Lidocaine: 1.0–1.5 mg/kg IV bolus, followed by 2–4 mg/min infusion 1

Procainamide may be preferred when amiodarone's delayed onset is unacceptable and the patient remains stable. 2