Dofetilide is a pure Class III antiarrhythmic that blocks cardiac potassium channels.

It prolongs repolarization and increases refractory period without significant sodium, beta, or calcium channel effects.

→ Dysrhythmias Module

• Selectively blocks IKr (rapid delayed rectifier potassium current) • Prolongs Phase 3 repolarization • Prolongs QT interval • Increases action potential duration

Net Effect:

• Suppresses atrial arrhythmias • Maintains sinus rhythm

Unlike Amiodarone, dofetilide has no multi-class effects.

• Rhythm control • Maintenance of sinus rhythm

• Safe in HFrEF • One of few rhythm agents allowed in systolic heart failure

→ Heart Failure Module

Dofetilide is NOT used for ventricular arrhythmias.

Dofetilide significantly prolongs QT interval.

Risk factors:

• Renal impairment • Hypokalemia • Hypomagnesemia • Concomitant QT-prolonging drugs

QT prolongation is dose-dependent.

Dofetilide must be initiated inpatient.

Requirements:

• Baseline ECG • Continuous telemetry • Serial QT measurements • Renal function assessment • Dose adjustment based on creatinine clearance

This requirement is exam-critical.

• Renally cleared • Requires dose adjustment in CKD • Minimal hepatic metabolism

Renal dosing is essential to reduce torsades risk.

• Baseline prolonged QT • Severe renal impairment • Concomitant QT-prolonging drugs • Electrolyte abnormalities

Avoid with strong CYP3A4 inhibitors.

Amiodarone: • Most effective • Multi-system toxicity • Lower torsades risk

Sotalol: • Beta-blocker + Class III • Also prolongs QT • Renally cleared

Dofetilide: • Pure Class III • Higher torsades risk • Requires inpatient initiation • Safe in HFrEF

✔ Pure potassium channel blocker ✔ Prolongs QT significantly ✔ High torsades risk ✔ MUST be started in hospital ✔ Safe rhythm-control agent in HFrEF

Related:

→ Dysrhythmias Module → Amiodarone → Sotalol → Heart Failure Module → Return to Cardiovascular Modules