Amiodarone: A Comprehensive Guide for Clinicians

Authors, Journal, Affiliations, Type, DOI

• David Hamilton Sr., Shuktika Nandkeolyar, Howard Lan, Pooja Desai, Jonathan Evans, Christopher Hauschild, Dimpa Choksi, Islam Abudayyeh, Tahmeed Contractor, Anthony Hilliard
• American Journal of Cardiovascular Drugs
• Loma Linda University Medical Center; University of Arizona Sarver Heart Center; UCLA; UC Irvine; Medical City McKinney
• Review article
• DOI: https://doi.org/10.1007/s40256-020-00401-5

Overview

Amiodarone is a class III antiarrhythmic that affects all four phases of the cardiac action potential through potassium, sodium, calcium channel blockade and non-competitive β-receptor blockade. It is widely used for both ventricular (VF, VT, ICD storm) and atrial (AF cardioversion, rhythm maintenance) arrhythmias. Long-term use carries significant multisystem toxicity risk — thyroid (4.4× RR), pulmonary fibrosis (1–2%, fatal 10%), hepatotoxicity, bradycardia, corneal microdeposits, and photosensitivity — requiring structured monitoring. Critical drug interactions include warfarin (30–50% dose reduction required), simvastatin/atorvastatin (CYP3A4), digoxin (p-glycoprotein), and sofosbuvir-containing HCV regimens (fatal bradycardia).

Keywords

Amiodarone, antiarrhythmic, class III, ventricular arrhythmia, atrial fibrillation, toxicity monitoring, drug interactions, thyroid, pulmonary fibrosis

Key Takeaways

Mechanism of Action

• Primarily classified as class III (IKr potassium channel blockade → prolongs action potential duration and QTc)
• Also inhibits: sodium channels (phase 0 / class I), L-type calcium channels (class IV), and non-competitive β-receptors (class II)
• IV amiodarone: acute effect predominantly via Na/Ca/β-blockade; class III effect delayed until active metabolite desethylamiodarone accumulates after loading

Pharmacokinetics

• Oral bioavailability 30–50%; absorption enhanced 2.4–3.8× with high-fat meal — take with food
• Three-phase distribution: central (24h) → peripheral/solid organ (7 days) → deep/fat tissue (4 weeks)
• Full VA antiarrhythmic effect reached at ~10 weeks of oral loading
• Half-life 50–60 days; drug continues to have effect for up to 3 months after discontinuation
• No renal dose adjustment required; initiate at low dose in hepatic impairment

Indications and Evidence

Ventricular Arrhythmias

• VF/Cardiac arrest: AHA ACLS Class IA recommendation; only antiarrhythmic in ACLS algorithm. ARREST trial: amiodarone vs placebo — higher survival to hospital admission (44 vs 34%). ALIVE trial: amiodarone superior to lidocaine in shock-resistant VF (22.8 vs 12.0%)
• Kudenchuk 2016 (n=3026): no survival benefit vs placebo in overall population; benefit seen in witnessed arrest subgroup only
• Hemodynamically tolerated VT: PROCAMIO RCT (n=62) showed procainamide superior to amiodarone for acute termination and safety — but amiodarone remains widely used due to familiarity
• ICD storm / recurrent VT: First-line for ICD shocks. OPTIC study: amiodarone + β-blocker had lowest rate of ICD shocks vs β-blocker alone or sotalol (though higher adverse event rate)
• VANISH trial: catheter ablation superior to drug escalation (including amiodarone) in ischaemic CMP with VA
• SCD-HeFT (n=2521): amiodarone showed no mortality benefit vs placebo in HFrEF (LVEF <35%) — does not replace ICD

Atrial Fibrillation

• Acute cardioversion: efficacy 35–65%; suitable for patients with ischaemic heart disease (unlike propafenone/flecainide)
• Rhythm control: pooled AFFIRM + AF-CHF meta-analysis (n=3307) — freedom from AF 84% at 1 year, 45% at 5 years
• AF with HF: catheter ablation superior to amiodarone (CASTLE-AF equivalent trial: 70% vs 34% AF-free at 2 years)
• Maintenance dose: 200 mg daily (consider 100 mg in elderly); maintenance initiated at 400 mg q8–12h × 1–2 weeks
• Risk of requiring pacemaker insertion higher in women and low body weight patients

Other SVT

• For stable flutter/AVNRT/AVRT: refer for catheter ablation (high cure rates) rather than long-term amiodarone
• Reserved for critically ill patients unable to undergo ablation

Dosing

• IV loading (VF/unstable VT): 150–300 mg bolus → 1 mg/min × 6h → 0.5 mg/min × ≥18h
• IV to oral conversion: if IV <1 week → 800–1600 mg/day PO; 1–3 weeks → 600–800 mg/day; >3 weeks → 400 mg/day
• Overlapping IV and oral amiodarone does not reduce early tachyarrhythmia recurrence

Drug Interactions

• Warfarin: CYP2C9/3A4 inhibition + inhibits S-warfarin; reduce warfarin dose by 30–50%; monitor INR closely
• Simvastatin: CYP3A4 inhibition; max simvastatin dose 20 mg with amiodarone; consider pravastatin (unaffected)
• Digoxin: p-glycoprotein inhibition → elevated digoxin levels → toxicity risk
• Class Ia antiarrhythmics (quinidine, procainamide, disopyramide): contraindicated — dose-independent QTc prolongation
• Class III agents: avoid combination — significant QTc prolongation
• Flecainide: reduce flecainide dose by 50% (CYP2D6 inhibition)
• β-blockers/CCBs: additive bradycardia and AV nodal block risk
• Sofosbuvir-containing HCV regimens (Harvoni, Sovaldi): FDA black box — rare but fatal bradycardia
• Indinavir/ritonavir (HIV): increase amiodarone concentration — Class X (avoid)
• Cholestyramine: reduces amiodarone bioavailability
• Ivabradine, fosphenytoin, lopinavir/ritonavir: additive QTc prolongation

Toxicities and Monitoring

Thyroid Management

• Hypothyroidism: levothyroxine; continue amiodarone for VT; stop for AF if alternatives exist
• Type I AIT (excess iodine synthesis in abnormal thyroid): methimazole 40–80 mg/day or PTU 400–800 mg/day; stop amiodarone
• Type II AIT (destructive thyroiditis in normal thyroid): prednisone 40–60 mg/day; may continue amiodarone initially; if no improvement in 1–2 months, stop amiodarone
• Refer to endocrinologist for thyroid toxicities

Pulmonary Management

• If toxicity suspected: stop amiodarone, refer to pulmonologist, start prednisone 40–60 mg/day
• Higher risk in pre-existing lung disease (severe asthma, COPD) or O₂-dependent patients

Cardiac Monitoring

• Asymptomatic bradycardia >40 bpm: maintain dose with monitoring
• HR <40 bpm: reduce dose by 50%, monitor for breakthrough arrhythmias
• Symptomatic bradycardia: reduce by 50% or stop; consider pacemaker (SVT) or ICD (VT) if intolerable arrhythmias recur

Pregnancy

• Class D drug: associated with cardiac, endocrine, and neurodevelopmental anomalies
• Use only as drug of last resort; avoid in breastfeeding or stop breastfeeding

Alternatives When Amiodarone Stopped

• VA: mexiletine, sotalol; rarely quinidine or procainamide (high TdP risk)
• AF: class Ic agents (no CAD/HF), dronedarone (structurally normal heart), sotalol/dofetilide (if eGFR adequate and QTc normal at baseline)

Monitoring Adherence

• Real-world adherence to monitoring guidelines is poor (multiple studies)
• Pharmacist-led amiodarone monitoring services improve screening compliance

Limitations of the Document

• Review article, not a systematic review or meta-analysis; evidence synthesis is narrative
• Key trials (ARREST, ALIVE, Kudenchuk 2016) cited but critical appraisal is limited
• PROCAMIO trial was small (n=62) — procainamide superiority conclusion has limited power
• Monitoring intervals suggested are largely based on expert consensus, not RCT evidence
• No separate management algorithms for paediatric populations

Key Concepts Mentioned

• concepts/Drug-Induced-Arrhythmia — QTc prolongation, TdP risk from drug combinations with amiodarone
• concepts/Torsades-de-Pointes — amiodarone-associated QTc prolongation; combinations that precipitate TdP
• concepts/Cardiac-Action-Potential — amiodarone inhibits all four phases
• concepts/Electrical-Storm — amiodarone as cornerstone therapy for VT storm
• concepts/LQTS-Pregnancy-Management — amiodarone Class D; contraindicated in pregnancy

Key Entities Mentioned

• entities/Atrial-Fibrillation — amiodarone for acute cardioversion and rhythm maintenance
• entities/Heart-Failure — SCD-HeFT: amiodarone no mortality benefit vs placebo in HFrEF
• entities/Long-QT-Syndrome — amiodarone prolongs QTc; combination with other QTc-prolonging drugs dangerous
• entities/Short-QT-Syndrome — amiodarone ineffective in SQTS1 (per channelopathies literature)

Wiki Pages Updated

• wiki/sources/amiodarone-cvdrug-2020.md — created
• wiki/sourceindex.md — updated
• wiki/wikiindex.md — updated
• wiki/entities/Atrial-Fibrillation.md — amiodarone section added
• wiki/entities/Heart-Failure.md — SCD-HeFT context updated
• wiki/concepts/Drug-Induced-Arrhythmia.md — amiodarone interaction context updated
• wiki/concepts/Torsades-de-Pointes.md — amiodarone QTc prolongation added