Procainamide
Antiarrhythmics
AntiarrhythmicsHigh alert
An error with this medicine can cause serious harm: double checks and protocols are used.
A class IA antiarrhythmic given intravenously for ventricular tachycardia. Long use can cause a lupus-like syndrome and serious blood disorders.
Quick facts
- Group
- Antiarrhythmics
- Target
- Cardiac sodium channel Nav1.5 (and potassium channels, through its metabolite NAPA)
- Key effects
- Hypotension with intravenous use · Nausea
- Monitor
- Continuous ECG · Blood pressure · Kidney function
- ATC
- C01BA02
No doses: the clinician sets them by the current guideline.
Mechanism of action
Procainamide blocks sodium channels (slower conduction, wider QRS) and lengthens repolarisation (longer QT): a class IA profile. Its liver metabolite N-acetylprocainamide (NAPA) blocks potassium channels and adds a class III effect. It is a peripheral vasodilator and can lower blood pressure when given quickly.
- Procainamide blocks sodium channels: slower conduction, wider QRS
- Repolarisation lengthens (longer QT), with help from its metabolite NAPA
- Re-entry in atria and ventricles is suppressed
Indications
- Documented life-threatening ventricular arrhythmias such as sustained ventricular tachycardia Ventricular tachycardia →
Adverse effects
Common
- Hypotension with intravenous use
- Nausea, vomiting and diarrhoea
- Positive antinuclear antibodies (ANA)
- Rash and fever
Contraindications
- Complete heart block (risk of asystole)
- Systemic lupus erythematosus
- Torsades de pointes
- Hypersensitivity to procainamide
- Caution in myasthenia gravis, which it can worsen
Key interactions
- Other class IA drugs (quinidine, disopyramide)
- More conduction slowing, depressed contractility and hypotension
- Other QT-prolonging drugs
- Higher risk of torsades de pointes
- Succinylcholine and other neuromuscular blockers
- Procainamide reduces acetylcholine release, so smaller doses of the blocker may be needed
What is monitored
- Continuous ECG: QRS width and QT
- Blood pressure, lying down, during the infusion
- Complete blood count and ANA with long-term use
- Kidney function; procainamide and NAPA levels where available
Administration and safety
- Given by slow intravenous injection or infusion with a pump, the patient lying down, with ECG and blood pressure monitoring.
- The infusion is stopped if hypotension or marked QRS widening appears, as the protocol states.
- A slightly yellow solution may be used; one darker than light amber is discarded.
Pregnancy and breastfeeding
Human data are lacking; it is used in pregnancy only if clearly needed. It passes into breast milk.
Nursing care
- Keep the patient supine and record blood pressure frequently during the infusion.
- Watch the monitor for QRS widening, QT prolongation and new arrhythmias.
- Ask about joint pain, chest pain on breathing, fever, sore throat or bruising during longer courses.
Pharmacokinetics
- Metabolism
- Partly acetylated in the liver to NAPA; fast acetylators make more NAPA than slow acetylators
- Elimination
- Kidneys (procainamide and NAPA); both accumulate in kidney failure and in older people
- Onset and duration
- Fast intravenously; intramuscular peaks within an hour
Test yourself
Think of the answer, then tap the question to see it.
Which autoimmune syndrome is classic with long-term procainamide?
Drug-induced lupus with positive ANA (arthralgia, serositis, fever), more frequent in slow acetylators.
What is NAPA and why does it matter?
N-acetylprocainamide, the active metabolite; it blocks potassium channels, prolongs the QT and accumulates in kidney failure.
Why is the blood count checked during procainamide treatment?
It can cause agranulocytosis and bone marrow depression, sometimes fatal.
Connections
← Back to the class: Antiarrhythmics
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - PROCAINAMIDE HYDROCHLORIDE injection, solution (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.