Is phenytoin (an antiepileptic drug) effective for treating ventricular tachycardia?

Phenytoin is NOT Recommended for Ventricular Tachycardia

Phenytoin is contraindicated for the treatment of ventricular tachycardia and should not be used for this purpose. 1 Current guidelines explicitly recommend against using phenytoin for ventricular tachycardia management, particularly in cases of severe toxicity with sustained ventricular arrhythmias.

First-Line Treatments for Ventricular Tachycardia

The management of ventricular tachycardia (VT) should follow this algorithm:

1. Assess hemodynamic stability:

   • If unstable: Immediate synchronized cardioversion
   • If stable: Proceed with pharmacological management

2. First-line pharmacological agents:

   • Amiodarone: Recommended for hemodynamically stable monomorphic VT with or without severe heart failure or acute myocardial infarction 1
   • Procainamide: Recommended for hemodynamically stable monomorphic VT without severe heart failure or acute myocardial infarction 1
   • Lidocaine: Used as a first-line agent for VT, particularly in the setting of acute ischemia 1

3. Second-line options:

   • Sotalol: May be considered for hemodynamically stable sustained monomorphic VT, including in patients with acute myocardial infarction 1
   • Beta-blockers: Effective for recurrent and refractory ventricular arrhythmias 1
   • Magnesium: May be effective for VF/VT, particularly when associated with acute myocardial infarction 1

Why Phenytoin is Contraindicated

The 2006 ACC/AHA/ESC guidelines for management of ventricular arrhythmias explicitly state that phenytoin is not recommended (Class III recommendation) for patients with severe toxicity presenting with sustained ventricular arrhythmias 1. This recommendation is based on evidence showing:

1. Lack of efficacy compared to other antiarrhythmic agents
2. Potential for proarrhythmic effects
3. Narrow therapeutic window with significant risk of toxicity
4. Potential for significant drug interactions

Special Considerations

Polymorphic VT/Torsades de Pointes

For polymorphic VT with long QT (torsades de pointes):

• Magnesium sulfate (first-line)
• Isoproterenol
• Temporary pacing
• Correction of electrolyte abnormalities

Refractory Cases

In cases of refractory VT:

• Consider catheter ablation
• Implantable cardioverter-defibrillator (ICD)
• Combination antiarrhythmic therapy under specialist guidance

Monitoring During Antiarrhythmic Therapy

When administering antiarrhythmic medications for VT:

• Continuous cardiac monitoring is essential
• Regular blood pressure measurements
• Monitor for signs of organ hypoperfusion
• Serial ECGs to assess QT interval and QRS duration
• Serum electrolyte monitoring, particularly potassium and magnesium

Pitfalls to Avoid

1. Do not use phenytoin for VT management - despite some older case reports suggesting potential benefit 2, 3, 4, current guidelines clearly contraindicate its use
2. Do not delay electrical cardioversion in unstable patients
3. Avoid verapamil in wide-complex tachycardias of unknown origin
4. Be cautious with flecainide/propafenone in patients with structural heart disease
5. Monitor for proarrhythmic effects of all antiarrhythmic drugs

While some limited research has explored phenytoin for specific ventricular arrhythmias in select populations 2, 3, 4, these studies are small, often case reports, and do not override the clear guideline recommendations against its use. The European Society of Cardiology has also downgraded or removed many antiarrhythmic drugs from their recommendations in recent years, emphasizing the need to follow current evidence-based protocols 1.