Procainamide

Procainamide is an important antiarrhythmic medication used in pediatric emergency medicine to manage various cardiac arrhythmias. It is classified as a Class IA antiarrhythmic agent according to the Vaughan Williams classification.

• Generic Name: Procainamide
• Brand Names: Pronestyl, Procan SR
• Drug Class: Class IA antiarrhythmic
• Available Forms: Injectable solution, oral tablets, extended-release capsules

Mechanism of Action

Procainamide exerts its antiarrhythmic effects through multiple mechanisms:

• Sodium channel blockade: Decreases the rate of rise of the action potential (phase 0)
• Potassium channel blockade: Prolongs the effective refractory period and action potential duration
• Anticholinergic effects: Increases AV node conduction and decreases automaticity of the SA node
• Decreases membrane responsiveness and excitability in ventricular and atrial tissue
• Slows conduction velocity, particularly in ischemic or depolarized tissues

Indications

In pediatric emergency medicine, procainamide is used for:

• Treatment of sustained ventricular tachycardia with a pulse
• Management of supraventricular tachycardias (SVT) refractory to adenosine
• Conversion of atrial fibrillation or atrial flutter to sinus rhythm
• Treatment of hemodynamically stable wide-complex tachycardias of unknown origin
• Management of accelerated idioventricular rhythm
• Suppression of premature ventricular contractions (PVCs)
• Treatment of Wolff-Parkinson-White syndrome with rapid conduction over an accessory pathway

Dosage and Administration

Dosing in pediatrics should be carefully calculated based on the child's weight and clinical situation:

• Loading dose (IV):
  • 10-15 mg/kg (maximum 100 mg/dose)
  • Administer over 30-60 minutes
  • May repeat every 5-10 minutes up to a maximum total dose of 15 mg/kg or 500 mg, whichever is lower
• Maintenance infusion:
  • 20-80 mcg/kg/minute
  • Titrate to effect and monitor ECG continuously
• Oral dosing (if transitioning to oral therapy):
  • 15-50 mg/kg/day divided into doses every 4-6 hours
  • Maximum daily dose: 4 g/day

Adverse Effects

Procainamide can cause several side effects, including:

• Cardiovascular:
  • QT interval prolongation (risk of Torsades de Pointes)
  • Hypotension (especially with rapid IV administration)
  • Bradycardia or heart block
  • Paradoxical tachyarrhythmias
• Gastrointestinal:
  • Nausea and vomiting
  • Anorexia
  • Diarrhea
• Central Nervous System:
  • Dizziness
  • Confusion
  • Psychosis (rare)
• Hematologic:
  • Agranulocytosis (rare but serious)
  • Neutropenia
• Immunologic:
  • Lupus-like syndrome (with prolonged use)
  • Myasthenia-like syndrome

Precautions and Considerations

• ECG monitoring: Continuous ECG monitoring is essential during administration
• QT prolongation: Use with caution in patients with pre-existing QT prolongation or those on other QT-prolonging medications
• Renal impairment: Dose adjustment is necessary in patients with renal dysfunction
• Hepatic impairment: Use with caution; may need dose adjustment
• Electrolyte imbalances: Correct hypokalemia and hypomagnesemia before administration
• Myasthenia gravis: May exacerbate symptoms
• Proarrhythmic potential: Can paradoxically worsen arrhythmias in some cases
• Drug interactions: Be aware of interactions with other antiarrhythmics and QT-prolonging drugs
• Conversion to oral therapy: Consider N-acetylprocainamide (NAPA) levels when transitioning to oral dosing