Class 3 Antiarrhythmics - Dofetilide & Ibutilide

Summary

Dofetilide and Ibutilide belong to the class 3 antiarrhythmics. These drugs treat arrhythmias like A-fib, where they are used for rhythm control, as well as atrial flutter. Dofetilide and ibutilide act primarily on non-nodal heart tissue and work by blocking potassium channels. This markedly prolongs the repolarization of heart cells, increases the length of the ERP, prolongs the AP duration, and increases the QT interval. These drugs can cause Torsades de Pointes as a rare side effect.

Key Points

• Ibutilide and Dofetilide
  • Drug Class
    • Class 3 Antiarrhythmic
  • Clinical Use
    • Treats A-Fib (atrial fibrillation)
      • Used for rhythm control
        • May be used for pharmacologic cardioversion (rare) as well as maintenance of normal sinus rhythm after electrical cardioversion (common)
        • Current cardiology guidelines recommend rate control (class 2 or 4 antiarrhythmics) before rhythm control (cardioversion); therefore, these drugs should be given later in the course of therapy
    • Treats Atrial Flutter
  • Mechanism
    • Primarily acts at non-nodal cardiomyocytes
      • Potassium-blocking actions of these drugs have greatest effects at non-nodal cells in heart
    • Blocks Potassium (K+) channels
      • Markedly prolongs repolarization by blocking potassium outflow
      • Increases effective refractory period (ERP)
      • Increases AP duration
      • Prolongs QT interval
        • Creates risk for early after-depolarizations and Torsades de Pointes
  • Side Effects
    • Torsades de Pointes
      • All drugs that increase QT interval increase the risk of early after-depolarizations causing ventricular arrhythmias like Torsades de Pointes.