Procainamide (CAS 51-06-9) is a class Ia antiarrhythmic medication used primarily to treat and prevent abnormal heart rhythms. Chemically, it is the amide analogue of the local anesthetic procaine, with significantly different pharmacological properties that make it valuable in cardiology. It is known for its therapeutic efficacy and a distinct side effect profile, particularly its association with drug-induced lupus.
Name :
ProcainamideCAS No. :
51-06-9MF :
C₁₃H₂₁N₃OMW :
235.33Purity :
97%Appearance :
a white to tan crystalline powderStorage Condition :
Solutions should be protected from light.Chemical Properties
Chemical Name: 4-Amino-N-(2-diethylaminoethyl)benzamide
IUPAC Name: 4-Amino-N-[2-(diethylamino)ethyl]benzamide
CAS Registry Number: 51-06-9
Molecular Formula: C₁₃H₂₁N₃O
Molecular Weight: 235.33 g/mol
Chemical Structure: Procainamide consists of a benzene ring substituted with an amino group (para-position) and an amide (–CONH–) linker connected to a diethylaminoethyl side chain. This amide bond, in contrast to the ester bond in procaine, confers greater metabolic stability and is key to its antiarrhythmic action.
Appearance: Typically a white to tan crystalline powder. The pharmaceutical product is commonly available as the hydrochloride salt (Procainamide HCl).
Solubility: Freely soluble in water and soluble in ethanol. The hydrochloride salt is highly water-soluble, which is suitable for intravenous formulation.
Stability: Stable under standard conditions. The amide bond is more resistant to hydrolysis than the ester bond in procaine, but it can degrade under extreme pH, temperature, or light exposure. Solutions should be protected from light.
Melting Point: The hydrochloride salt melts at approximately 165-169 °C.
pKa: Approximately 9.2 (for the alkylamino group), which influences its ionization state and pharmacokinetics.
Biological Activities
Primary Activity: Class Ia Antiarrhythmic Agent. Its main mechanism is the blockade of cardiac voltage-gated sodium channels, particularly in their open/activated state. This action:
1.Decreases conduction velocity in the atria, ventricles, and Purkinje fibers.
2.Prolongs the action potential duration and effective refractory period.
3.Suppresses abnormal automaticity (e.g., in ectopic foci).
Metabolism and Active Metabolite: It is acetylated in the liver by the enzyme N-acetyltransferase 2 (NAT2) to form N-Acetylprocainamide (NAPA), which is also pharmacologically active (a Class III antiarrhythmic, primarily prolonging repolarization). The acetylation rate is genetically determined, leading to "fast" and "slow" acetylator phenotypes, which influences dosing and side effect risk.
Pharmacokinetics: Well-absorbed orally (~75-90%), with a relatively short half-life (2-4 hours for the parent drug; 6-10 hours for NAPA), necessitating frequent dosing or use of sustained-release formulations. It is excreted renally (50-60% unchanged).
Side Effects/Adverse Activities:
Cardiovascular: Hypotension (especially with IV use), QT prolongation, torsades de pointes (a life-threatening arrhythmia).
Immunological: Drug-induced lupus erythematosus (dILE) is a well-known adverse effect, especially in slow acetylators. Symptoms may include arthralgia, myalgia, pleuritis, and rash. Unlike systemic lupus, renal and CNS involvement is rare, and symptoms typically resolve upon drug discontinuation.
Other: Nausea, rash, agranulocytosis (rare but serious).
Biosynthesis
Procainamide is not biosynthesized by living organisms; it is produced by chemical synthesis.
The classic synthetic route involves the condensation of 4-aminobenzoic acid (PABA) with N,N-diethylethylenediamine in the presence of a coupling agent to form the amide bond.
Alternatively, it can be synthesized by modifying procaine, replacing the ester linkage with an amide group, which aligns with its historical discovery as a more stable, cardiologically active analogue.
Applications
FAQs
Q1: What is the main difference between procaine and procainamide?
A1: Procaine is an ester-based local anesthetic with a very short duration due to rapid plasma hydrolysis. Procainamide is an amide-based compound designed to resist hydrolysis. Its primary action is as a Class I antiarrhythmic drug for the heart, not as a local anesthetic. The amide group provides metabolic stability and different target organ effects.
Q2: Why is monitoring important during procainamide therapy?
A2: Close therapeutic drug monitoring (TDM) of both procainamide and its metabolite NAPA is essential to:
Ensure therapeutic levels (procainamide: 4-10 µg/mL; combined procainamide + NAPA: 10-30 µg/mL).
Minimize toxicity risks, especially life-threatening cardiac effects like QT prolongation and torsades de pointes.
Guide dosing in patients with renal impairment, as both parent drug and NAPA are renally excreted.
Q3: What is procainamide-induced lupus, and who is at risk?
A3: It is an autoimmune syndrome caused by the drug, mimicking symptoms of systemic lupus erythematosus (e.g., joint pain, fever, rash, pleurisy). Slow acetylators (individuals with low NAT2 enzyme activity) are at higher risk because they metabolize the drug more slowly, leading to higher exposure and the formation of reactive metabolites that may trigger the autoimmune response. Symptoms usually resolve after stopping the drug.
Q4: Is procainamide still used today?
A4: Yes, but its use has become more selective. It remains an important therapeutic option, particularly for:
Acute treatment of hemodynamically stable ventricular tachycardia.
Management of arrhythmias in specific contexts (e.g., in Wolff-Parkinson-White syndrome).
Due to its side effect profile (especially lupus and proarrhythmia), it is often not a first-line long-term therapy, with drugs like amiodarone or sotalol being preferred in many cases.
Q5: Can I buy procainamide (CAS 51-06-9) for research?
A5: Yes, it is available from reputable chemical and pharmaceutical reference standard suppliers for legitimate research and development purposes. It is sold as a chemical or pharmaceutical standard. Important: Procainamide is a prescription drug strictly regulated for human and veterinary therapeutic use. Research purchases require appropriate institutional documentation and must comply with all applicable regulations, with no intent for unauthorized human or animal administration.
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