What is the recommended IV amiodarone dosing and administration protocol for acute atrial fibrillation, including loading dose, maintenance infusion, monitoring, and contraindications?

IV Amiodarone Administration for Atrial Fibrillation

For acute atrial fibrillation, administer IV amiodarone as a 150 mg bolus over 10 minutes, followed by 1 mg/min for 6 hours (360 mg), then 0.5 mg/min for 18 hours (540 mg), with a maximum total dose of 2.2 g over 24 hours. 1, 2, 3

Loading Dose Protocol

• Initial bolus: 150 mg IV over 10 minutes for acute rate control or cardioversion 1, 2, 3
• Early maintenance infusion: 1 mg/min for 6 hours (delivers 360 mg) 1, 2, 3
• Late maintenance infusion: 0.5 mg/min for 18 hours (delivers 540 mg) 1, 2, 3
• Maximum 24-hour dose: 2.2 g total 1, 2, 3

Alternative rapid loading regimens have been studied but are less standardized:

• 5–7 mg/kg over 30–60 minutes followed by continuous infusion has shown 55–95% conversion rates 1, 4
• Most conversions occur after 6–8 hours of therapy, not immediately 2, 3, 4

Mandatory Monitoring Requirements

Continuous cardiac monitoring is required throughout the infusion because hypotension occurs in approximately 16% of patients, with additional risks of bradycardia and AV block 2, 3

• Blood pressure monitoring every 15–30 minutes initially, with readiness to reduce infusion rate or add vasopressors 2
• Daily 12-lead ECG to assess QT interval and detect new heart block; hold therapy if QT >500 ms 2
• Heart rate checks every 4–6 hours initially, then at least once daily 2
• Continuous telemetry for ≥24 hours after IV discontinuation 2

Expected Efficacy

• Conversion to sinus rhythm typically occurs after 6–8 hours of therapy, not within the first 1–2 hours 1, 2, 4
• Conversion rates: 34–69% with bolus-only regimens and 55–95% with bolus plus continuous infusion 2, 4
• Predictors of successful conversion include shorter AF duration, smaller left atrial size, and higher amiodarone dose 1, 4
• Amiodarone is not superior to Class IC drugs (flecainide, propafenone) for rapid conversion but is safer in structural heart disease 1, 4

Patient-Specific Indications

Amiodarone is the preferred antiarrhythmic in patients with heart failure or reduced ejection fraction because Class IC agents are contraindicated in structural heart disease 2, 3, 4

• Class IIa recommendation for rate control in Wolff-Parkinson-White syndrome with accessory pathways when conversion or ablation is not immediately feasible 1, 3
• Safe in renal impairment because amiodarone undergoes hepatic metabolism, not renal excretion; no dose adjustment needed 2, 3
• Relatively contraindicated in significant pulmonary disease; if no alternative exists, use the lowest effective dose for the shortest duration 2, 3

Critical Drug Interactions During IV Therapy

Reduce digoxin dose by 50% immediately when amiodarone is started because amiodarone roughly doubles digoxin levels 2

• Reduce warfarin dose by 30–50% and obtain INR check 3–5 days after initiation; amiodarone markedly increases INR 2
• Reduce or discontinue beta-blockers and calcium-channel blockers as amiodarone's rate-control effect develops to avoid excessive bradycardia 2
• Avoid coadministration with other QT-prolonging medications without expert consultation 5, 3

Transition to Oral Therapy

Begin oral loading while the IV infusion continues at 0.5 mg/min, using a duration-based conversion strategy that accounts for tissue drug already accumulated 2, 5

• If IV therapy <1 week: start oral 800–1600 mg daily 2, 5
• If IV therapy 1–3 weeks: start oral 600–800 mg daily 2, 5
• If IV therapy >3 weeks: start oral 400 mg daily 2, 5
• Continue IV infusion at 0.5 mg/min for 24 hours after the first oral dose, then discontinue 2
• Continue oral loading until cumulative 10 g dose is achieved, then switch to maintenance 200–400 mg daily 2, 5

Common Pitfalls to Avoid

• Do not expect immediate conversion: amiodarone's full antiarrhythmic effect requires days to weeks despite therapeutic serum levels due to its extremely long half-life (26–107 days) 2, 5
• Do not use peripheral IV for prolonged infusions: administer through central venous catheter to avoid phlebitis 6
• Do not combine with other rate-controlling agents initially: amiodarone provides rate control on its own and combination increases bradycardia risk 1, 2
• Do not use in WPW with AF alongside beta-blockers, digoxin, adenosine, or calcium-channel blockers: these can precipitate ventricular fibrillation 3