Procainamide Dosing for VT Conversion
For conversion of hemodynamically stable monomorphic VT, procainamide should be administered at 20-50 mg/min until arrhythmia suppression occurs, with a typical effective dose range of 500-1000 mg (approximately 7.5-15 mg/kg), though the maximum cumulative dose is 17 mg/kg. 1, 2, 3
Standard Loading Protocol
The FDA-approved dosing regimen for IV procainamide involves two acceptable approaches 2:
Direct IV injection method: Administer 100 mg every 5 minutes at a rate not exceeding 50 mg/min until arrhythmia suppression, hypotension develops, QRS widens by 50%, or a total of 500 mg is given; after 500 mg, wait 10 minutes before resuming if needed 2
Loading infusion method: Administer 20 mg/mL solution at 1 mL/min for 25-30 minutes to deliver 500-600 mg total; effects may appear after 100-200 mg, and it is unusual to require more than 600 mg 2
Maximum total loading dose: 1 gram (17 mg/kg) regardless of administration method 1, 2
Expected Dose for Conversion
Clinical evidence demonstrates variable dose requirements for VT termination 3, 4, 5:
Lower doses (7.5 mg/kg or ~500 mg): Suppress VT induction in approximately 17-25% of patients 4, 6
Moderate doses (15 mg/kg or ~1000 mg): Achieve VT suppression in an additional 24% of patients, bringing total response rate to approximately 40-50% 4, 6
Median effective dose: Studies show a median dose of 600 mg (range 100-1080 mg) successfully terminates hemodynamically stable VT in 93% of patients 5
Critical Monitoring Parameters
Stop the infusion immediately if any of the following occur 1, 2:
- Arrhythmia suppression (desired endpoint)
- Hypotension develops
- QRS duration prolongs by ≥50% from baseline
- Total cumulative dose of 17 mg/kg is reached
- Bradycardia occurs
Maintenance Infusion After Conversion
Once VT is suppressed, transition to maintenance infusion 2:
- Standard concentration: 2 mg/mL (1000 mg in 500 mL D5W) at 1-3 mL/min
- Fluid-restricted patients: 4 mg/mL (1000 mg in 250 mL D5W) at 0.5-1.5 mL/min
- Target maintenance rate: 2-6 mg/min (approximately 50 mcg/min/kg) to maintain therapeutic plasma levels of ~6.5 mcg/mL 2
Important Clinical Considerations
Procainamide is not first-line therapy for VT 1, 3:
- The 1996 ACC/AHA guidelines position procainamide after lidocaine and bretylium for VF/pulseless VT 1
- The 2015 AHA guidelines give procainamide no specific recommendation for cardiac arrest, noting it was studied as a second-tier agent with no survival benefit demonstrated 1
- For hemodynamically stable monomorphic VT, procainamide receives a Class IIa recommendation (higher than amiodarone's IIb), making it the preferred medical option if cardioversion is not performed 3
Special Populations and Contraindications
Avoid or use extreme caution in 1, 7:
- Patients with QT prolongation (risk of torsades de pointes)
- Congestive heart failure (negative inotropic effects)
- Renal insufficiency (accumulation of active metabolite NAPA increases torsades risk) 1, 7
- Hypotension at baseline 1, 2
Dose adjustments for renal impairment and age 2:
- Advancing age reduces renal excretion by ~25% at age 50 and ~50% at age 75, independent of creatinine clearance
- Maintenance infusion rates must be reduced accordingly to prevent toxicity
Common Pitfalls to Avoid
- Never administer the full 1000 mg as a rapid bolus - this significantly increases hypotension risk; always respect the 50 mg/min maximum rate 2
- Do not assume non-inducibility at one dose predicts response at higher doses - 3 of 5 patients non-inducible at 7.5 mg/kg had VT reinduced at higher doses 4, 6
- Monitor for proarrhythmia - new VT morphologies (often faster) can be induced in ~40-50% of patients during procainamide administration 4
- Recognize the paradox of dose-dependent efficacy - some patients respond at lower concentrations but lose efficacy at higher concentrations, suggesting a therapeutic window rather than a simple dose-response relationship 6