Antiarrhythmic
Procainamide
Indications
- Stable monomorphic VT or regular wide-complex tachycardia (ACLS; fewer major events than amiodarone in PROCAMIO)
- Life-threatening ventricular arrhythmias such as sustained VT (label)
- Pre-excited AF (WPW) in a stable patient (off-label)
- Conversion of recent-onset AF or flutter (off-label)
- Brugada provocation testing in the EP lab (off-label)
Dosing
Procainamide drip card and mL/h converterStart: Load 20–50 mg/min until the arrhythmia stops, hypotension, QRS widens by over 50%, or 17 mg/kg is given
| Where | Dose |
|---|---|
| Rhythm control | Procainamide: 20–50 mg/min until the rhythm converts, hypotension, QRS widens over 50% or 17 mg/kg; then 1–4 mg/min |
On the quick cards
Mechanism of action
Procainamide is a Vaughan Williams class Ia drug: it binds open fast Na⁺ channels (Nav1.5) with intermediate kinetics, slowing phase 0 and conduction in atria, ventricles, His–Purkinje fibers and accessory pathways, which widens the QRS. It also blocks IKr, lengthening action potential duration, refractoriness and the QT, and its metabolite NAPA is an almost pure class III K⁺ channel blocker. Weak ganglionic blockade and a vagolytic action explain hypotension and slightly faster AV conduction.
Pharmacology
- Cardiovascular: QRS and QT widen with the level; slowing accessory-pathway conduction suits it to pre-excited AF
- Cardiovascular: hypotension during loading; contractility usually holds, but output can fall in heart failure (label)
- Autonomic: vagolytic speeding of AV conduction can raise the ventricular rate in flutter (label)
- Neuromuscular: less acetylcholine release; worsens myasthenia gravis and potentiates neuromuscular blockers (label)
- Immune: ANA turns positive in many long-term users, with a lupus-like syndrome in up to 30% on long-term oral therapy (label)
Pharmacokinetics
| Onset | IV: therapeutic levels within minutes (label) |
|---|---|
| Half-life | 3–4 h, shorter in fast acetylators; NAPA about 6–8 h; both far longer in kidney failure |
| Distribution | Vd about 2 L/kg; hydrophilic (label) |
| Protein binding | 15–20% (label) |
| Metabolism | Liver NAT2 acetylates it to active NAPA: 16–21% of a dose in slow acetylators, 24–33% in fast (label) |
| Elimination | Urine: 30–60% unchanged and 6–52% as NAPA; NAPA clearance is almost entirely renal (label) |
| Acetylator status | 40–60% of people of European or African ancestry are slow acetylators: more procainamide, less NAPA, and earlier ANA |
| Therapeutic levels | Procainamide 4–10 mcg/mL; procainamide plus NAPA 10–30 mcg/mL |
| Dialysis | Hemodialysis removes both; peritoneal dialysis does not (label) |
Chemistry
- 4-amino-N-[2-(diethylamino)ethyl]benzamide: procaine with an amide in place of the ester, so plasma esterases spare it and it lasts hours, not minutes
- Achiral tertiary amine, pKa 9.23 (label): about 98% ionized at pH 7.4 and water soluble
- Its aromatic amine can be oxidized to reactive hydroxylamines linked to lupus; NAPA, acetylated at that amine, does not cause lupus
- 100 and 500 mg/mL vials with methylparaben and sodium metabisulfite, pH 4–6; discard if darker than light amber (label)
Adverse effects and cautions
In the one-pagers
- Rhythm GallerySinus, atrial and junctional: AF with WPW (fast, irregular, wide): no AV-nodal blockers (adenosine, diltiazem, beta-blockers, digoxin, amiodarone). Unstable: cardiovert. Stable: procainamide or ibutilide.
- Myasthenic Crisis and Guillain-Barré SyndromeMyasthenic crisis: Worsen MG: fluoroquinolones (boxed warning), aminoglycosides, macrolides, IV magnesium, β-blockers, procainamide, neuromuscular blockers, volatile anesthetics, checkpoint inhibitors
- ACLS Algorithms in BriefTachycardia with a pulse: Or procainamide 20–50 mg/min; stop at 17 mg/kg, hypotension or QRS widening over 50%; avoid in long QT or heart failure
- CEN Mental Health: Crisis, Suicide Risk, Eating Disorders and AbuseHyperventilation and caffeine: Caffeine (Willson 2018): a Red Bull can holds about 80 mg and a Monster about 160 mg, and one 473 mL product held 357 mg. Roughly 1 g may cause toxic symptoms, 2 g may need hospital care and 5 g or more is typically lethal; tachycardia is near universal above 10 mg/kg. Mild toxicity is irritability, palpitations, nausea, tremor and sweating; severe toxicity brings ve
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In the algorithms
Other antiarrhythmic drugs
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Sources
- FDA label: Procainamide injection, Hospira (2023)
- FDA label: Nexterone (2024, interactions)
- Labcorp: procainamide and NAPA levels
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.