Class III Antiarrhythmics - Amiodarone



Amiodarone is an antiarrhythmic drug primarily used for rhythm control, or the correction of bad heart rhythms. It is a Class III antiarrhythmic, which means that it works by blocking potassium channels. Like the other class 3 antiarrhythmics, amiodarone can prolong the QT interval, leading to increased risk of torsades de pointes.

Specific side effects to note with amiodarone are CYP450 inhibition, hepatotoxicity, pulmonary fibrosis, and thyroid dysfunction.

Key Points

  • Amiodarone
    • Mechanism
      • Class 3 Antiarrhythmic
        • Along with Ibutilide, Dofetilide, Sotalol, and Bretylium
      • Blocks Potassium (K+) channels
        • Prolongs phase 3 repolarization by blocking potassium outflow, mainly in non-nodal tissue
        • Increases AP duration and effective refractory period (ERP)
          • Prolonged QT creates risk for early after-depolarizations and Torsades de Pointes
    • Clinical Use
      • Atrial flutter/fibrillation
      • Ventricular tachycardia
        • Amiodarone is used in ACLS (along with epinephrine) for codes
    • Adverse Effects
      • Pulmonary fibrosis
      • Thyroid dysfunction
        • AmIODarone is 40% IODine by weight
        • Serum TSH should be measured before starting and monitored during course
      • Hepatotoxicity
        • Elevated LFTs may be seen
      • Long QT (Torsades de Pointes risk)
        • All drugs that increase QT interval increase the risk of early after-depolarizations causing ventricular arrhythmias like Torsades de Pointes.
      • CYP450 inhibitor
        • Interacts with warfarin; both may be used in atrial fibrillation
      • Acts as hapten (corneal deposits, blue/gray skin discoloration)
      • Neurological effects
      • Constipation
      • Cardiovascular depression (bradycardia, heart block, heart failure)