Amiodarone

Introduction to Amiodarone

Amiodarone is a potent antiarrhythmic medication used in pediatric emergency medicine for the treatment of various life-threatening arrhythmias.

Key Points:

Class III antiarrhythmic drug
Used for both supraventricular and ventricular arrhythmias
Complex pharmacokinetics with a very long half-life
Available in both intravenous and oral formulations
Requires careful monitoring due to potential for serious side effects

Pharmacology of Amiodarone

Amiodarone has a complex pharmacological profile, affecting multiple ion channels and receptors in the heart.

Mechanism of Action:

Primarily blocks potassium channels (Class III effect)
Also exhibits Class I, II, and IV antiarrhythmic properties
Prolongs action potential duration and effective refractory period
Decreases sinoatrial node automaticity
Slows AV nodal conduction

Pharmacokinetics:

Onset of action: IV - minutes to hours; PO - days to weeks
Duration of action: Prolonged due to tissue accumulation
Half-life: Extremely long (20-100 days)
Metabolism: Hepatic via CYP3A4 and CYP2C8
Excretion: Primarily biliary

Clinical Applications in Pediatric Emergency Medicine

Amiodarone is used in various critical cardiac situations in pediatrics, particularly when other treatments have failed.

Indications:

Ventricular fibrillation (VF): Refractory to defibrillation
Pulseless ventricular tachycardia (VT): Refractory to defibrillation
Hemodynamically unstable VT with pulse
Supraventricular tachycardia (SVT): Refractory to other treatments
Postoperative junctional ectopic tachycardia

Contraindications:

Severe sinus node dysfunction
Second or third-degree AV block (unless functioning pacemaker is present)
Known hypersensitivity to amiodarone or iodine
Severe hepatic dysfunction

Dosing and Administration

Amiodarone dosing in pediatrics varies based on the clinical scenario and route of administration.

Pediatric Dosing for Cardiac Arrest (IV/IO):

Initial dose: 5 mg/kg rapid bolus (max 300 mg)
Subsequent doses: May repeat up to 2 times for refractory VF/pulseless VT

Pediatric Dosing for Perfusing Arrhythmias (IV/IO):

Loading dose: 5 mg/kg over 30-60 minutes (max 300 mg)
Infusion: 5-15 mcg/kg/min

Administration Considerations:

For IV administration, use a concentration of 1.5-6 mg/mL
Use a dedicated IV line or port for administration
Continuous cardiac monitoring is essential during administration
For non-emergent loading, can be given orally in divided doses over several days

Adverse Effects and Precautions

Amiodarone has a wide range of potential adverse effects, some of which can be serious or life-threatening.

Common Adverse Effects:

Bradycardia
Hypotension (especially with rapid IV administration)
QT interval prolongation
Nausea and vomiting
Constipation

Serious Adverse Effects:

Proarrhythmia (including torsades de pointes)
Pulmonary toxicity (including pneumonitis and fibrosis)
Hepatotoxicity
Thyroid dysfunction (both hyper- and hypothyroidism)
Corneal microdeposits (with long-term use)
Peripheral neuropathy

Precautions and Monitoring:

Baseline and periodic monitoring of liver function tests, thyroid function, and pulmonary function
Regular ECG monitoring for QT prolongation and bradyarrhythmias
Avoid concurrent use of other QT-prolonging medications when possible
Use with caution in patients with hepatic impairment
Monitor for drug interactions, especially with CYP3A4 inhibitors/inducers