Procainamide
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
