Unit Converter
N‑acetylprocainamide (NAPA)
Synonym
N acetylprocainamide, N‑acetyl-procainamide, NAPA
Units of measurement
µmol/L, mg/L, mg/dL, mg/100mL, mg%, µg/mL
N-ACETYLOPROCAINAMIDE (NAPA)
(Active Metabolite of Procainamide — Major Therapeutic Drug Monitoring Marker in Cardiac Arrhythmias)
Synonyms
- N-acetylprocainamide
- NAPA
- Acetylprocainamide
- APA
- Procainamide metabolite
Units of Measurement
- µmol/L
- mg/L
- mg/dL
- mg/100 mL
- mg%
- µg/mL
Molecular Weight
264.3 g/mol
Key Unit Conversions
Molar ↔ Mass
1 mg/L=3.78 µmol/L1\ \text{mg/L} = 3.78\ \text{µmol/L}1 mg/L=3.78 µmol/L 1 µmol/L=0.264 mg/L1\ \text{µmol/L} = 0.264\ \text{mg/L}1 µmol/L=0.264 mg/L
mg/dL ↔ mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
µg/mL
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
mg%
\text{mg%} = \text{mg/dL}
Description
N-acetylprocainamide (NAPA) is the major active metabolite of the antiarrhythmic drug procainamide.
Produced via hepatic N-acetylation, NAPA has:
- Class III antiarrhythmic properties
- Longer half-life than procainamide
- Important role in overall therapeutic and toxic effects
Therapeutic drug monitoring (TDM) of both procainamide + NAPA is essential because:
- Each has independent pharmacologic activity
- Total drug effect = procainamide + NAPA
- Renal failure causes NAPA accumulation, increasing toxicity risk
Physiological Role
None — NAPA is a pharmacologic compound, not naturally occurring.
Clinical Significance
Therapeutic Uses
NAPA contributes to management of:
- Ventricular arrhythmias
- Atrial arrhythmias
- Supraventricular tachycardia (SVT)
- Atrial fibrillation conversion in some cases
NAPA is especially important in long-term procainamide therapy.
HIGH NAPA Levels (Toxicity)
Symptoms
- Hypotension
- Bradyarrhythmias
- QRS or QT prolongation
- Torsades de pointes (most feared complication)
- Dizziness, syncope
- CNS effects
- Seizures (rare)
Major Causes
- Renal impairment (primary cause)
- High procainamide dose
- Slow acetylators vs fast acetylators (pharmacogenetic variability)
- Drug interactions (cimetidine, amiodarone)
- Heart failure or shock (reduced clearance)
NAPA increases QT interval more readily than procainamide → higher risk of torsades.
LOW NAPA Levels
Indicate:
- Subtherapeutic dosing
- Poor procainamide metabolism
- Hyperfiltration (rare)
- Very recent dose (before steady state)
- Non-adherence
Reference Intervals (Therapeutic Ranges)
(Tietz 8E + Mayo + ARUP + ACCP TDM)
Therapeutic Range
- 10 – 30 mg/L
(= 10–30 µg/mL)
(= 38 – 113 µmol/L)
Toxic Range
- > 40 mg/L
(= > 40 µg/mL)
(= > 150 µmol/L)
Combined Level Interpretation
(Total antiarrhythmic activity = procainamide + NAPA)
- Combined 10–30 mg/L → desired
- Combined > 30–40 mg/L → caution
- Combined > 40 mg/L → high toxicity risk
Units Description
mg/L
Most common clinical reporting unit.
µg/mL
Equivalent to mg/L.
µmol/L
Preferred in pharmacokinetic studies.
mg/dL / mg%
Older units used in older pharmacology literature.
Diagnostic Uses
1. Therapeutic Drug Monitoring (Primary Use)
Used to adjust procainamide therapy.
2. Evaluate Suspected Toxicity
- QT prolongation
- Arrhythmias
- Hypotension
- Wide QRS complex
3. Monitor Renal Failure Patients
NAPA clearance is almost entirely renal → accumulation is common.
4. Optimize Antiarrhythmic Therapy
Maintaining combined levels within therapeutic range reduces:
- Recurrence of arrhythmias
- Drug-induced proarrhythmia
- Mortality in acute arrhythmia management
Analytical Notes
- Sample: serum or plasma
- Trough level preferred (just before next dose)
- LC–MS/MS or immunoassay used
- Hemolysis & lipemia interfere with chromatographic assays
- Levels shift significantly with acute renal changes
- Measure both procainamide + NAPA simultaneously
Clinical Pearls
- NAPA is more pro-arrhythmic (QT-prolonging) than procainamide.
- In renal failure, NAPA accumulates rapidly — monitor closely.
- Fast/slow acetylators (genetics) alter procainamide → NAPA ratio.
- Therapeutic effect depends on combined drug levels, not either alone.
- If QTc > 500 ms → suspect NAPA toxicity.
- For torsades, discontinue drug + give IV magnesium.
Interesting Fact
NAPA is structurally similar to procainamide but has longer half-life, giving it more stable plasma concentrations — which is why total drug monitoring must include both molecules.
SEO Unit Converter Text
N-acetylprocainamide converter — convert between µmol/L, mg/L, mg/dL, mg%, and µg/mL. Includes therapeutic/toxic ranges, renal adjustment notes, and combined procainamide–NAPA interpretation.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition — Therapeutic Drug Monitoring
- ACCP Guidelines on Therapeutic Drug Monitoring
- Mayo Clinic Laboratories — NAPA
- ARUP Consult — Antiarrhythmic Drug TDM
- MedlinePlus / NIH — Procainamide & Metabolites