What intravenous amiodarone bolus dose should be given to a hemodynamically stable ICU patient with rapid‑ventricular‑response atrial fibrillation and no contraindications?

Amiodarone Bolus Dose for Hemodynamically Stable Atrial Fibrillation with Rapid Ventricular Response

Administer 150 mg of intravenous amiodarone infused over 10 minutes as the initial bolus, followed by a continuous infusion of 1 mg/min for 6 hours (360 mg), then 0.5 mg/min for the remaining 18 hours, with a maximum total dose of 2.2 g over 24 hours. 1, 2, 3, 4

Standard Loading Protocol

The FDA-approved and guideline-recommended regimen consists of three distinct phases 4:

• Initial bolus: 150 mg diluted in 100 mL D5W infused over 10 minutes 1, 2, 4
• Early maintenance: 1 mg/min continuous infusion for 6 hours (total 360 mg) 1, 2, 3
• Late maintenance: 0.5 mg/min continuous infusion for 18 hours (total 540 mg) 1, 2, 3
• Maximum 24-hour dose: Do not exceed 2.2 g total 1, 2, 4

Breakthrough Episodes

If the patient experiences recurrent rapid ventricular response or fails to achieve adequate rate control during the infusion, you may repeat the 150 mg bolus over 10 minutes 1, 4. This supplemental bolus can be given as needed for breakthrough episodes while continuing the maintenance infusion 1.

Expected Time to Effect

Conversion to sinus rhythm typically occurs 6–8 hours after initiating therapy, not within the first 1–2 hours. 2, 5 The overall conversion rate with bolus-plus-infusion regimens ranges from 55–95%, significantly higher than the 34–69% seen with bolus-only protocols 2, 5. In one randomized trial of patients with atrial fibrillation and ventricular rates >135 bpm, 28% converted to sinus rhythm by 30 minutes and 42% by 60 minutes after a high-dose bolus 6.

Critical Monitoring Requirements

Cardiovascular Surveillance

• Continuous cardiac monitoring is mandatory throughout the infusion 3, 4
• Blood pressure monitoring every 15–30 minutes during the bolus and hourly during maintenance, as hypotension occurs in approximately 16% of patients 2, 3
• Daily 12-lead ECG to assess QT interval (hold therapy if QT >500 ms) and detect new heart block 2, 3
• Heart rate checks every 4–6 hours initially, then at least daily 2

Adverse Effects to Anticipate

• Hypotension (16%): Slow or temporarily stop the infusion; add vasopressors, positive inotropic agents, or volume expansion as needed 2, 3, 4
• Bradycardia (4.9% with IV therapy): Reduce infusion rate or discontinue 2, 3, 4
• AV block: Discontinue if second- or third-degree block develops without a functioning pacemaker 2, 4
• Phlebitis: Use a central line when possible; peripheral administration caused superficial phlebitis in 1 patient in one trial 6

Drug Interactions Requiring Immediate Adjustment

Amiodarone inhibits multiple cytochrome P450 enzymes and P-glycoprotein, necessitating dose reductions of concomitant medications 3:

• Digoxin: Reduce dose by 50% immediately, as amiodarone doubles digoxin levels 2, 3
• Warfarin: Reduce dose by 30–50% and check INR within 3–5 days, as amiodarone significantly increases INR 2, 3
• Beta-blockers and calcium-channel blockers: Do not combine at initiation; excessive bradycardia risk is high 2

Special Population Considerations

Structural Heart Disease or Heart Failure

Amiodarone is the preferred antiarrhythmic in patients with heart failure, reduced ejection fraction, or structural heart disease, where class IC agents (flecainide, propafenone) are contraindicated. 2, 5 Use with caution in moderate-to-severe left ventricular dysfunction due to potential negative inotropic effects 2, 3.

Wolff-Parkinson-White Syndrome

Amiodarone is a Class IIa option for rate control in WPW patients with atrial fibrillation when immediate cardioversion or ablation is not feasible 2. Avoid beta-blockers, digoxin, adenosine, and calcium-channel blockers in this population, as they can precipitate ventricular fibrillation 2.

Renal Impairment

No dose adjustment is required, as amiodarone undergoes hepatic metabolism rather than renal excretion 2, 3.

Pulmonary Disease

Amiodarone is relatively contraindicated in significant lung disease; if no alternative exists, use the lowest effective dose for the shortest duration 2, 3.

Common Pitfalls to Avoid

• Infusing too rapidly: The 150 mg bolus must be given over a full 10 minutes to minimize hypotension 1, 4
• Combining with other rate-control agents at initiation: This markedly increases bradycardia risk; wait until amiodarone's rate-control effect is established (approximately 6 weeks) before cautiously reintroducing beta-blockers or calcium-channel blockers 2
• Expecting immediate conversion: Most conversions occur after 6–8 hours, not within minutes 2, 5
• Exceeding 2.2 g in 24 hours: This increases toxicity without additional benefit 1, 4

Predictors of Successful Conversion

Higher likelihood of conversion to sinus rhythm is associated with 5:

• Shorter duration of atrial fibrillation
• Smaller left atrial size
• Higher cumulative amiodarone dose (>1500 mg/day)