PROCAINAMIDE HYDROCHLORIDE

Clinical safety rating: safe

Animal studies have demonstrated safety

How it works

Class Ia antiarrhythmic agent; blocks sodium channels, slowing conduction velocity and prolonging refractory period in atrial and ventricular myocardium.

What the body does with it

Metabolism	Hepatic acetylation via N-acetyltransferase (NAT2) to N-acetylprocainamide (NAPA); CYP2D6 minor pathway.
Excretion	Renal: ~50-60% unchanged via glomerular filtration and tubular secretion; hepatic metabolism to N-acetylprocainamide (NAPA, active) accounts for ~15-30% of dose, further eliminated renally; biliary/fecal: negligible (<5%).
Half-life	Terminal elimination half-life: 2.5-5 hours (normal renal function); prolonged to 11-20 hours in renal impairment (e.g., CrCl <30 mL/min); clinical context: requires dosing adjustment in renal failure; NAPA half-life: 6-8 hours (normal), up to 40 hours in renal failure.
Protein binding	~15-20% bound to serum albumin and alpha-1-acid glycoprotein; low binding minimizes displacement interactions.
Volume of Distribution	Vd: 1.5-2.5 L/kg (total body water); extensive tissue distribution (e.g., heart, liver, kidneys); clinical meaning: large Vd indicates substantial extravascular distribution, requiring loading doses for rapid therapeutic effect.
Bioavailability	Oral: 75-95% (immediate-release); IM: 100%; sustained-release oral: ~90% (relative to immediate-release).
Onset of Action	IV: immediate (within 1-2 minutes); IM: 10-30 minutes; oral: 30-60 minutes (fasted state); peak effect oral: 1-2 hours.
Duration of Action	IV/IM: 3-4 hours (antiarrhythmic effect); oral immediate-release: 3-6 hours; sustained-release oral: 8-12 hours; clinical note: duration correlates with plasma concentration >4 mcg/mL.

Classification & Brands

Dosing & administration

Oral: 250-500 mg every 3-6 hours. IV: Loading dose 15-18 mg/kg infused over 25-30 minutes, then maintenance infusion 1-4 mg/min. Maximum total daily dose: 4 g.

Dosage form	CAPSULE
Renal impairment	CrCl 10-50 mL/min: administer every 6-12 hours. CrCl <10 mL/min: administer every 8-24 hours. For IV: reduce maintenance infusion rate proportional to CrCl.
Liver impairment	Child-Pugh Class A: no adjustment; Class B: reduce dose by 25-50%; Class C: avoid use or reduce dose by 50-75% with monitoring.
Pediatric use	Oral: 15-50 mg/kg/day divided every 3-6 hours. IV: Loading dose 15-18 mg/kg; maintenance 20-80 mcg/kg/min. Maximum: 100 mg/kg/day.
Geriatric use	Start with lower doses (e.g., 250 mg oral every 6 hours) due to age-related renal decline. Monitor for hypotension and toxicity. Adjust based on CrCl.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Other drugs that prolong the QT interval increase risk of torsades de pointes Can cause lupus-like syndrome and blood dyscrasias.

Breastfeeding	Present in breast milk in low concentrations; M/P ratio approximately 0.4-0.6. Considered compatible with breastfeeding by American Academy of Pediatrics; monitor infant for bradycardia or hypotension.
Teratogenic Risk	FDA Pregnancy Category C. First trimester: Limited human data; animal studies suggest potential fetal harm. Second/third trimesters: May cause maternal hypotension reducing placental perfusion; use only if clearly needed. Risk of neonatal arrhythmias if used near term.

Warnings & precautions

■ FDA Black Box Warning

May cause severe blood dyscrasias (e.g., agranulocytosis, neutropenia, thrombocytopenia) and drug-induced lupus erythematosus.

Side Effect Profile

Common Effects	Lupus-like syndrome
Serious Effects

Absolute Contraindications

Complete heart block, second-degree AV block, torsade de pointes, systemic lupus erythematosus, hypersensitivity to procainamide or procaine.

Clinical Precautions

Precautions

Monitor CBC regularly; discontinue if blood dyscrasias occur. Prolonged QT interval risk; caution with other QT-prolonging drugs. May exacerbate heart failure or hypotension. Reduce dose in renal impairment.

Clinical Tips & Counseling

Drug interactions

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