VS ACLS | Lidocaine v Amiodarone

80/20 Comparative Summary: Amiodarone vs. Lidocaine

1. Class & Mechanism of Action

• Amiodarone (Cordarone): Class III antiarrhythmic with Class I, II, III, and IV actions[1][2]. Primarily blocks potassium channels in phases 2 and 3, delaying repolarization and prolonging effective refractory period[1]. Weakly blocks sodium channels (phase 0 upstroke), depresses SA/AV automaticity, blocks calcium channels, noncompetitively inhibits alpha/beta receptors, and causes vasodilation[2][3].
• Lidocaine: Class IB antiarrhythmic and amide local anesthetic[4]. Selectively inhibits fast sodium channel influx in phase 0, shortening action potential duration and refractory period in His-Purkinje tissue while suppressing automaticity/reentry preferentially in ischemic myocardium[6]. Blocks nerve sodium channels for local anesthesia[7].

2. Indications & ACLS Role

• Amiodarone: Indicated for life-threatening recurrent ventricular fibrillation (VF), hemodynamically unstable ventricular tachycardia (VT), and atrial fibrillation[8]. Used in ACLS CPR for VF/pVT unresponsive to defibrillation[11][12].
• Lidocaine: Indicated IV for acute life-threatening VF/VT (post-MI/cardiac surgery) and ACLS CPR[5][13]. Used topically/regionally for local anesthesia[4][14]. In pediatric ACLS, associated with higher return of spontaneous circulation (ROSC) rates than amiodarone[15][16].

3. Pharmacokinetics & Administration

• Amiodarone: Oral, IV, or IO route[17]. Lipophilic (Vd ~70 L/kg), delayed steady state (1–5 months), and long terminal half-life (mean 53 days)[19][20]. Hepatically metabolized via CYP3A4/2C8 to active metabolite DEA[21]. Dilute in D5W only, use volumetric pumps and in-line filters, and avoid PVC containers/tubing for long infusions due to drug adsorption and DEHP leaching[22].
• Lidocaine: Administered IV, IO, IM, topically, or transdermally[4]. Rapid IV onset (immediate) with short duration (10–20 min)[27]. Hepatically metabolized via CYP1A2/3A4 to MEGX and GX; >98% excreted renally[28][29]. Given as IV bolus load followed by continuous infusion[13][30].

4. Adverse Effects & Safety Warnings

• Amiodarone: Boxed warnings for pulmonary toxicity (up to 17%), fatal hepatotoxicity, and proarrhythmia (QT prolongation, Torsades de Pointes)[31]. Contains ~37% iodine, causing thyroid dysfunction[36]. Causes hypotension, phlebitis (>3 mg/mL), corneal deposits, and photosensitivity[32]. Contraindicated in 2nd/3rd degree AV block, SSS, and severe bradycardia[33].
• Lidocaine: Toxicity causes CNS effects (seizures, confusion, dysarthria) and cardiovascular collapse (bradycardia, hypotension, arrest)[40]. Boxed warning prohibits viscous lidocaine for infant teething pain[44]. Requires 50% infusion rate reduction after 24 hours or in heart failure/hepatic impairment[30].