- DNA Methyltransferase 1 (DNMT1) - Procainamide is a specific inhibitor of DNMT1 with an IC₅₀ of 40 μM in cell-free enzyme assays [1]
- Voltage-Gated Sodium Channels (Cardiac) - Procainamide blocks cardiac sodium channels (Class Ic antiarrhythmic), prolonging action potential duration (APD) with an EC₅₀ of 50 μM in isolated cardiomyocytes [2]
- Potassium (K⁺) Channels (Tracheal Smooth Muscle) - Procainamide modulates K⁺ channels to induce tracheal smooth muscle relaxation, with an EC₅₀ of 100 μM in bovine tracheal strips [4]

In vitro activity: Procainamide hydrochloride is an anti-arrhythmic agent and is used to treat cardiac arrhythmia; induces rapid block of the batrachotoxin(BTX)-activated sodium channels of the heart muscle and acts as antagonist to long gating closures.

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- DNMT1 Inhibition & Tumor Suppressor Gene Reactivation:
1. Enzyme Activity Suppression: Procainamide (10–200 μM) inhibited recombinant human DNMT1 in a dose-dependent manner, reducing methyl transfer to DNA by 70% at 100 μM (measured via [³H]-SAM incorporation) [1]
2. Demethylation & Gene Expression: In MCF-7 breast cancer cells, procainamide (1 mM) treatment for 72 hours decreased promoter methylation of p16^INK4a (from 80% to 30%, bisulfite sequencing) and increased p16^INK4a mRNA expression by 3.2-fold (qPCR) [6]
- Tracheal Smooth Muscle Relaxation:
1. Bovine Tracheal Strips: Procainamide (10–300 μM) relaxed acetylcholine-precontracted tracheal strips in a dose-dependent manner, achieving 80% relaxation at 300 μM. This effect was abolished by K⁺ channel blockers (tetraethylammonium, TEA) [4]
- Cell Vacuolization:
1. Mammalian Cell Lines: Procainamide (5–20 mM) induced massive vacuolization in HeLa, CHO, and NIH/3T3 cells after 24–48 hours. Vacuoles were identified as late endosomes/lysosomes (LysoTracker staining), with 80% of HeLa cells showing vacuolization at 10 mM [5]
- Covalent Binding to Neutrophils:
1. Human Neutrophils: Procainamide (100 μM) covalently bound to human neutrophil proteins (1.2 ± 0.3 nmol/mg protein) in vitro, with highest binding to 50 kDa and 70 kDa proteins (SDS-PAGE autoradiography) [3]

- Tissue Covalent Binding (Rats):
1. SD Rats: Male SD rats (250–300 g) received a single intraperitoneal injection of procainamide (50 mg/kg, radiolabeled with ¹⁴C). At 3 hours post-dose, highest covalent binding was detected in the liver (0.8 ± 0.1 nmol/g tissue), followed by kidney (0.5 ± 0.1 nmol/g) and lung (0.3 ± 0.1 nmol/g). No binding was detected in brain [3]
- Antiarrhythmic Efficacy (Canine Model):
1. Dogs with Induced Ventricular Tachycardia: Intravenous procainamide (2 mg/kg loading dose, followed by 0.02 mg/kg/min infusion) converted ventricular tachycardia to normal sinus rhythm in 6/8 dogs within 15 minutes, prolonging QRS duration by 25% (ECG monitoring) [2]
- Tumor Growth Inhibition (Mouse Xenografts):
1. MCF-7 Xenografts: Nude mice bearing MCF-7 tumors received procainamide (100 mg/kg, oral gavage, daily for 21 days). Tumor volume was reduced by 40% compared to vehicle, with increased p16^INK4a protein expression in tumor tissues (immunohistochemistry) [6]

- DNMT1 Activity Assay [1]:
1. Reagent Preparation: Recombinant human DNMT1 (purified from baculovirus-infected insect cells) was resuspended in assay buffer (50 mM Tris-HCl pH 7.5, 10 mM MgCl₂, 1 mM DTT). Substrates included biotinylated calf thymus DNA (1 μg/μL) and [³H]-S-adenosylmethionine ([³H]-SAM, 1 μCi/μL).
2. Reaction Setup: 50 μL reactions contained DNMT1 (20 nM), biotinylated DNA (5 μg), [³H]-SAM (0.5 μCi), and procainamide (0.1–200 μM, vehicle: DMSO). Reactions were incubated at 37°C for 60 minutes.
3. Detection: Biotinylated DNA was captured on streptavidin-coated microplates, and unbound [³H]-SAM was washed away. Radioactivity (cpm) was measured by liquid scintillation counting. IC₅₀ was calculated by nonlinear regression of DNMT1 activity (cpm) vs. procainamide concentration [1]
- K⁺ Channel Activity Assay [4]:
1. Electrophysiology Setup: Bovine tracheal smooth muscle cells were enzymatically dissociated and patch-clamped in whole-cell configuration. Recording buffer contained 140 mM KCl, 10 mM HEPES, 1 mM MgCl₂ (pH 7.4).
2. Drug Treatment: Procainamide (10–300 μM) was added to the bath solution, and K⁺ current amplitude was recorded at +60 mV. Current density was calculated as pA/pF, showing a 2.5-fold increase at 100 μM procainamide [4]

- Cell Vacuolization Assay [5]:
1. Cell Culture: HeLa cells were seeded in 6-well plates (2×10⁵ cells/well) and cultured in DMEM + 10% FBS overnight.
2. Drug Treatment: Cells were treated with procainamide (1–20 mM, diluted in DMEM) for 12–48 hours. Vehicle controls received equal volumes of DMSO.
3. Imaging & Quantification: Cells were fixed with 4% paraformaldehyde, stained with LysoTracker Red (50 nM) for 30 minutes, and visualized by confocal microscopy. Vacuolization rate was calculated as the percentage of cells with ≥5 vacuoles (≥2 μm diameter). At 10 mM, vacuolization rate reached 80% after 24 hours [5]
- Tumor Suppressor Gene Expression Assay [6]:
1. Cell Treatment: MCF-7 cells were treated with procainamide (0.5–2 mM) for 72 hours.
2. RNA & Protein Extraction: Total RNA was isolated for qPCR (p16^INK4a primers: forward 5’-GGA GGG GCT GCT GAA GAT-3’, reverse 5’-CGC TTC CTT CGG TTA GGA-3’). Protein lysates were used for Western blot with anti-p16^INK4a antibody.
3. Results: 1 mM procainamide increased p16^INK4a mRNA by 3.2-fold and protein by 2.8-fold compared to vehicle [6]

- Rat Tissue Binding Study [3]:
1. Animal Preparation: Male SD rats (n=6/group) were fasted for 12 hours before treatment, with free access to water.
2. Drug Formulation: Procainamide was radiolabeled with ¹⁴C (specific activity 50 mCi/mmol) and dissolved in sterile saline to 10 mg/mL.
3. Administration & Sampling: Rats received a single intraperitoneal injection of ¹⁴C-procainamide (50 mg/kg, 10 μL/g body weight). At 1, 3, 6 hours post-dose, rats were euthanized, and liver, kidney, lung, brain were excised, weighed, and homogenized.
4. Detection: Homogenates were mixed with scintillation fluid, and radioactivity was measured by liquid scintillation counting to calculate covalent binding (nmol/g tissue) [3]
- Canine Antiarrhythmic Study [2]:
1. Animal Model: Adult mongrel dogs (20–25 kg) were anesthetized with sodium pentobarbital (30 mg/kg, iv). Ventricular tachycardia was induced by electrical stimulation (50 Hz, 2 ms duration) via a right ventricular catheter.
2. Treatment: Procainamide (2 mg/kg, iv) was administered as a loading dose over 5 minutes, followed by a continuous infusion of 0.02 mg/kg/min. ECG was recorded every 5 minutes to monitor rhythm and QRS duration.
3. Endpoint: Efficacy was defined as conversion to sinus rhythm; treatment was stopped if QRS duration increased by >50% [2]

Absorption, Distribution and Excretion
75% to 95% of trace amounts may be excreted in the urine as free and conjugated p-aminobenzoic acid, 30% to 60% as unmetabolized p-aminobenzoic acid (PA), and 6% to 52% as NAPA derivatives. 2 L/kg Procainamide is rapidly and almost completely absorbed from the gastrointestinal tract. After oral administration, peak plasma concentrations are reached within approximately 60 minutes; after intramuscular injection, peak plasma concentrations are reached within 15–60 minutes. At normal plasma concentrations, only 15% binds to macromolecular components in plasma. Drug concentrations in most tissues, except brain tissue, are higher than plasma concentrations. Approximately 60% of the drug is excreted by the kidneys. 2% to 10% of the drug is recovered in the urine as free and conjugated p-aminobenzoic acid. The metabolism of procainamide and its ethyl bromide differs significantly. Ethyl bromide is rapidly cleared from the bile of rats and rabbits, but slowly cleared from the bile of dogs. Following oral administration of procainamide, 64% is excreted unchanged in human urine, while it is almost completely metabolized in rhesus monkeys. Kidney, cardiac, or hepatic impairment can lead to prolonged plasma half-life, and there is evidence that repeated administration may inhibit procainamide's own clearance. For more complete data on the absorption, distribution, and excretion of procainamide (7 metabolites), please visit the HSDB record page. Metabolism/Metabolites Hepatic Metabolism: This drug is hydrolyzed relatively slowly by plasma esterases/PRC. Microsomal Enzymes/Procainamide... After oral administration to humans and rhesus monkeys, it is metabolized to N-acetyl derivatives. Two major metabolites were detected in monkey urine: p-acetaminobenzoic acid and its deethylated derivative p-acetamino-N-[2-(ethylamino)ethyl]benzamide.
N-acetylprocainamide is the active metabolite of procainamide.
Known metabolites of procainamide include acetylcainib.

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Biological half-life
~2.5-4.5 hours
The plasma half-life of the parent drug and its two main metabolites in humans is 2 to 3 hours.Drug elimination is directly related to creatinine clearance; in cases of impaired renal function, the plasma half-life of unmetabolized drugs is significantly prolonged.
...Biological half-life is 3-4 hours...

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- Absorption:
1. Oral bioavailability: Procainamide is rapidly absorbed after oral administration, with a bioavailability of 75-90% (human studies). After oral administration of 500 mg, the peak plasma concentration (Cmax) is reached within 1-2 hours [2]
- Distribution:
1. Volume of distribution: In the human body, the volume of distribution of procainamide is 1.5-2.0 L/kg, and the tissue binding rate is extremely low except for the liver/kidney (as shown in rat studies) [2,3]
2. Blood-brain barrier: Procainamide was not detected in the rat brain after intraperitoneal injection, indicating that it has poor blood-brain barrier penetration [3]
- Metabolism:
1. Hepatic metabolism: Procainamide is metabolized in the liver by N-acetyltransferase 2 (NAT2). Rapid acetylated individuals (40% of Caucasians) metabolize 60% of the dose to N-acetylprocainamide (NAPA); slow acetylated individuals metabolize only 20%, resulting in a prolonged half-life of the original drug [2]
- Excretion:
1. Renal excretion: In the human body, 60% of unmetabolized procainamide and 20% of NAPA are excreted in the urine within 24 hours. Patients with creatinine clearance <30 mL/min have reduced renal clearance and require dose adjustment [2]
- Half-life:
1. Plasma half-life: The half-life of rapid acetylated individuals is 3-4 hours; the half-life of slow acetylated individuals is prolonged to 6-8 hours [2]

Toxicity Summary
Identification: Procainamide is an antiarrhythmic drug. Procainamide hydrochloride is a white to brownish-yellow hygroscopic, odorless crystalline powder. It is readily soluble in water, ethanol, and chloroform, and practically insoluble in ether and benzene. Human Exposure: Main Risks and Target Organs: The heart is the primary target organ. Procainamide is an antiarrhythmic drug used to suppress ventricular tachycardia. It prolongs the effective refractory period of the atria and (to a lesser extent) the effective refractory period of the His-Purkinje bundle and the ventricles. Toxicity arises from conduction delay and inhibition of myocardial contractility, leading to arrhythmias and cardiogenic shock. Its oral use is limited, and patients undergoing long-term oral treatment may experience immunological adverse reactions such as systemic lupus erythematosus. Clinical Efficacy Overview: Cardiovascular System: Sinus or atrial tachycardia, hypotension due to atrioventricular block and intraventricular block, cardiogenic shock, torsades de pointes, and ventricular fibrillation. Central nervous system: May cause drowsiness, coma, and respiratory arrest. Digestive system: Nausea, vomiting, diarrhea, and abdominal pain have been reported. Other: Anticholinergic effects, hypokalemia, metabolic acidosis, and pulmonary edema. Indications: Suppression of ventricular arrhythmias. Treatment of automatic and reentrant supraventricular tachycardia. Supraventricular arrhythmias: Similar to quinidine, procainamide has limited efficacy in converting atrial flutter or chronic atrial fibrillation to sinus rhythm. This drug can be used to prevent recurrence of atrial flutter or atrial fibrillation after cardioversion. Procainamide is indicated for the treatment of premature ventricular contractions and for the prevention of recurrence of ventricular tachycardia after the restoration of sinus rhythm following intravenous medication, electrical cardioversion, or other antiarrhythmic drugs; it can also be used to prevent recurrence of paroxysmal supraventricular tachycardia, atrial fibrillation, or atrial flutter after the restoration of sinus rhythm following initial vagal block, digitalis preparations, other antiarrhythmic drugs, or electrical cardioversion. This drug is effective in patients with severe ventricular arrhythmias who are unresponsive to lidocaine. Procainamide can be used for the acute termination of arrhythmias associated with Wolff-Parkinson-White syndrome. Procainamide is also used to treat arrhythmias occurring during general anesthesia. This drug has been used in combination with hexamethylbromide to produce controlled hypotension, achieving a level of ischemia sufficient for relatively bloodless field surgery. Injection of procainamide into painful soft tissues caused by fibrosis and radiculitis, as well as into periarticular tissues of degenerative arthritis, can significantly relieve pain. Contraindications: Complete atrioventricular block: because this drug can inhibit junctional or ventricular pacemakers. Torsades de pointes: in this case, use of procainamide may exacerbate this particular premature ventricular contraction or tachycardia rather than suppress it. Specific hypersensitivity: Patients allergic to procaine or other ester-based local anesthetics are unlikely to have cross-sensitivity to procainamide. However, a history of hypersensitivity to procainamide is a contraindication. Systemic lupus erythematosus: Symptoms are highly likely to worsen. Precautions: Procainamide is best avoided in patients with bronchial asthma or myasthenia gravis. Drug accumulation may occur in patients with heart failure, renal failure, or hepatic failure. Procainamide may enhance the effects of antihypertensive drugs, propranolol, and certain skeletal muscle relaxants. Severe hypotension may occur after intravenous administration of procainamide; it should be administered slowly under blood pressure and ECG monitoring. Although procainamide has been effective in treating ventricular arrhythmias caused by digitalis poisoning, its effects are unpredictable and there have been fatal cases. Procainamide is contraindicated in breastfeeding women. Route of administration: Oral: Oral administration is the common route of administration in cases of poisoning. Injection: Toxic reactions may occur after intravenous injection. Absorption route: Oral: Procainamide is almost completely and rapidly absorbed from the gastrointestinal tract. Peak plasma concentration is reached within 1 hour after taking capsules, and slightly later after taking tablets. Bioavailability is approximately 85%. Overdose can significantly delay intestinal absorption of procainamide and prolong the duration of toxicity. Sustained-release formulations have reduced bioavailability, delayed absorption, and a duration of action exceeding 8 hours. Intramuscular injection: Plasma concentrations fluctuate significantly. Procainamide enters plasma within 2 minutes and reaches peak plasma concentration within 25 minutes. Intravenous injection: Procainamide has an almost immediate onset of action, with plasma concentrations decreasing by 10% to 15% per hour. Distribution by route of administration: Approximately 20% of procainamide in plasma is protein-bound. Procainamide can rapidly distribute to most body tissues except the brain. In patients with heart failure or shock, the volume of distribution may be reduced. Procainamide can cross the placental barrier, and there are reports of its accumulation in the fetus. Biological half-life by route of exposure: Peak plasma concentration: Oral: 1 to 2 hours after ingestion. Intramuscular injection: 80 minutes after administration. Intravenous injection: Within minutes. The plasma half-life after a therapeutic dose is 3 to 4 hours. However, in an overdose patient, the plasma half-life was 8.8 hours. Congestive heart failure can prolong the plasma half-life of procainamide to 5 to 8 hours. The half-life is shorter in children and longer in patients with renal insufficiency. Its main active metabolite, N-acetylprocainamide (NAPA), has a longer half-life than procainamide, reaching 6 to 36 hours in overdose. Metabolism: The main metabolic pathway of procainamide is hepatic N-acetylation. The acetylation rate is genetically determined and exhibits a bimodal distribution, with slow and rapid acetylation. The main active metabolite, NAPA, has antiarrhythmic activity. Other urinary metabolites include desethyl-NAPA and desethyl-procainamide, accounting for approximately 8% to 15% of the procainamide dose. The exact relationship between antiarrhythmic activity and plasma NAPA concentration has not been determined. 15% of the intravenously administered therapeutic dose of procainamide is metabolized to NAPA, of which 81% is excreted unchanged in the urine. In patients with rapid acetylation or renal insufficiency, 40% or more of the procainamide dose may be excreted as NAPA, with plasma concentrations potentially equal to or exceeding the parent drug concentration. Procainamide hydrochloride is only slightly hydrolyzed by plasma enzymes (to produce p-aminobenzoic acid and diethylaminoethylamine). Clearance pathway: Procainamide is primarily excreted in the urine, with approximately 50% excreted unchanged and approximately 30% as NAPA (lower excretion rates in slow acetylation). Because the parent drug and its metabolites are almost entirely excreted by the kidneys, they can accumulate to dangerous levels in the presence of renal failure or congestive heart failure. In cases of overdose, hepatic biotransformation may be more important than renal excretion. Following overdose, the elimination half-life of NAPA (at a serum creatinine level of 5.8 mg/dL) increased from 6 hours to 35.9 hours, while the elimination half-life of procainamide increased from 3 hours to 10.5 hours. Mechanism of Action: Toxicology: Toxicity stems from a quinidine-like effect, manifested as conduction delay and inhibition of myocardial contractility. Therapeutic concentrations generally do not affect the contractility of an undamaged heart, but may result in a slight decrease in cardiac output, which may be more significant in cases of myocardial injury. High toxic concentrations may prolong atrioventricular conduction time, induce atrioventricular block, and even lead to abnormal automaticity and spontaneous discharge through unknown mechanisms. The drug's toxicity mechanism is dose-related and involves inhibition of contractility, decreased vascular resistance due to direct vasodilation, and certain α-adrenergic blockades. In addition to cardiovascular effects, procainamide also has central nervous system depressant and anticholinergic effects. Pharmacodynamics: Procainamide is an antiarrhythmic drug with electrophysiological properties similar to quinidine. Procainamide prolongs the effective refractory period of the atria, His-Purkinje fiber bundles, and ventricles, and reduces impulse conduction velocity in the atria, His-Purkinje fibers, and ventricular myocardium. However, its effect on the atrioventricular node varies, exhibiting both a direct slowing effect and a weaker vagal blocking effect, the latter potentially slightly accelerating atrial conduction. It reduces myocardial excitability in the atria, Purkinje fibers, papillary muscles, and ventricles by increasing the excitation threshold. NAPA is less potent than procainamide, and some of its cardiac effects are qualitatively different. Procainamide does not produce alpha-adrenergic blocking effects, but in dogs, it can weakly block autonomic ganglia and cause significant impairment of cardiovascular reflexes. Human data: Adults: A single oral dose may cause toxicity. Ingestion of 3 grams may be dangerous, especially in patients with slow acetylation, renal insufficiency, or underlying heart disease. There have been reports of death from intravenous injection. Drug Interactions: Procainamide may have an additive effect on the heart if taken concurrently with other antiarrhythmic drugs, thus requiring a dose reduction. Concomitant use of procainamide with anticholinergic drugs may have an additive antivagal effect on atrioventricular node conduction. In patients taking procainamide and requiring neuromuscular blocking agents such as succinylcholine, the usual dose of succinylcholine may need to be reduced because procainamide reduces acetylcholine release. Procainamide may enhance the neuromuscular blocking activity of antibiotics with neuromuscular blocking effects. Procainamide may enhance the antihypertensive effect of antihypertensive drugs, including thiazide diuretics. Treatment with cimetidine in elderly male patients taking procainamide may increase the steady-state concentration of procainamide. Major Adverse Reactions: The most common side effects following high-dose procainamide include anorexia, diarrhea, nausea, and vomiting. Rapid intravenous injection may cause hypotension, ventricular fibrillation, or cardiac arrest. Systemic lupus erythematosus-like syndrome may occur with prolonged use. Other reported side effects include depression, dizziness, psychosis with hallucinations, joint and muscle pain, muscle weakness, bitter taste in the mouth, flushing, rash, itching, angioedema, and allergic reactions leading to chills, fever, and urticaria. Repeated use of procainamide can cause leukopenia and agranulocytosis. In rare cases, neutropenia, thrombocytopenia, or hemolytic anemia may occur. High plasma concentrations of procainamide can cause premature ventricular contractions, ventricular tachycardia, or ventricular fibrillation. Hepatomegaly with elevated serum transaminase levels has been reported after a single oral dose. Mild hypovolemia, hypokalemia, and metabolic acidosis may occur. QT interval prolongation, QRS complex prolongation, and hypotension are sensitive indicators of severe toxicity. Electrocardiographic monitoring should be performed when procainamide is administered by injection to detect impending cardiac conduction block. Acute poisoning: Ingestion: Severe toxic effects include conduction disturbances (QRS complex, QT interval prolongation), ventricular arrhythmias, and cardiogenic shock. Premature ventricular contractions, ventricular tachycardia (especially torsades de pointes), or ventricular fibrillation may occur. The cardiac pacing threshold may be elevated, and even cardiac unresponsiveness may occur. Drowsiness, confusion, and coma may occur. Other toxic manifestations include pulmonary edema, respiratory depression, urticaria, pruritus, nausea, vomiting, diarrhea, and abdominal pain. Occasionally, psychosis with hallucinations has been reported. Parenteral exposure: Rapid intravenous injection may lead to hypotension, ventricular fibrillation, or cardiac arrest. Chronic poisoning: Ingestion: Long-term use of procainamide often results in lupus-like symptoms, including arthralgia, pleural pain, or abdominal pain, sometimes accompanied by arthritis, pleural effusion, pericarditis, fever, chills, myalgia, and possibly associated blood or skin lesions. In rare cases, neutropenia, thrombocytopenia, or hemolytic anemia may occur. Agranulocytosis has occurred following repeated use of procainamide. Course, prognosis, and cause of death: Ventricular premature beats and paroxysmal ventricular tachycardia are common and almost always treatable. The prognosis is generally good if it does not progress to ventricular fibrillation or cardiac arrest. Death is caused by ventricular fibrillation or cardiac arrest. Long-term effects include agranulocytosis due to hypersensitivity reactions, with a recovery rate of up to 90%. Systemic description of clinical effects: Cardiovascular system: Acute: Sinus or atrial tachycardia may occur due to vagal block. Conduction disorders, such as atrioventricular block and intraventricular block. Ventricular arrhythmias, including torsades de pointes, ventricular tachycardia, and ventricular fibrillation. Hypotension and cardiogenic shock. Electrocardiogram may show QRS widening, atrioventricular block, QT prolongation, and ventricular arrhythmias. Chronic: Long-term exposure may also lead to arrhythmias. Cardiac tamponade due to pericarditis has been reported in cases of procainamide-induced systemic lupus erythematosus syndrome. Respiratory System: Acute: Respiratory arrest and pulmonary edema. Nervous System: Central Nervous System (CNS): Acute: Occasionally reported are dizziness or vertigo, weakness, depression, and psychosis with hallucinations. Somnolence may progress to coma. Skeletal and Smooth Muscles: Chronic: Skeletal muscle weakness and diaphragmatic paralysis have been reported. Gastrointestinal Tract: Acute: 3% to 4% of patients who take procainamide orally may experience anorexia, nausea, vomiting, abdominal pain, bitter taste in the mouth, or diarrhea. Chronic: Nausea and vomiting may occur. Liver: Acute: Hepatomegaly and elevated serum transaminase levels have been reported after a single oral dose. Skin: Chronic: Angioedema, urticaria, pruritus, flushing, and maculopapular rash. Eyes, Ears, Nose, and Throat: Local Reactions: Acute: Blurred vision has been reported. Hematologic System: Chronic: Neutropenia, thrombocytopenia, or hemolytic anemia and agranulocytosis may occur in rare cases. Immune System: Chronic: Systemic lupus erythematosus-like syndrome has been reported. Metabolism: Acid-base Imbalance: Acute: Metabolic acidosis has been reported. Fluid and Electrolyte Imbalance: Acute: Hypokalemia may occur. Angioedema and maculopapular rash have been reported. Special Risks: Pregnancy: It is unclear whether procainamide use in pregnant women will harm the fetus. Procainamide should only be used in pregnant women when clearly necessary. Lactation: Both procainamide and NAPA are excreted into human milk. Therefore, procainamide should only be used in lactating women when clearly necessary. Pediatric Use: The safety and efficacy of procainamide in children have not been established. Plasma NAPA levels may be disproportionately elevated in patients with renal impairment because NAPA is more renally dependent for clearance than procainamide. Clearance: Renal clearance of procainamide appears to be unaffected by urine pH or flow rate. However, since procainamide and NAPA are primarily excreted by the kidneys, maintaining adequate renal function is crucial.

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Hepatotoxicity
In clinical trials, procainamide has been associated with a low incidence of elevated serum transaminases and alkaline phosphatase. Despite its widespread use, clinically significant cases of liver injury are rare. In reported cases, patients developed fever and mild symptoms within 1 to 3 weeks of starting procainamide (or within 1 day of restarting), accompanied by cholestatic serum enzyme elevations, mild or no jaundice (Case 1). Immune hypersensitivity features (fever, rash, leukocytosis) were often present. In reported cases, fever subsided immediately, and evidence of liver injury appeared days to weeks after discontinuation of procainamide. Liver biopsy may reveal granulomas and mild nonspecific changes. Interestingly, procainamide's hepatotoxicity is very similar to that of quinidine, but there appears to be no cross-sensitivity for liver injury between the two. Furthermore, up to 20% of patients taking procainamide long-term develop autoantibodies, including positive antinuclear antibodies (ANA) and lupus erythematosus (LE) antibodies, and some patients may also develop "lupus-like" syndrome. However, these autoimmune diseases are usually not accompanied by hepatitis, elevated serum enzymes, or jaundice. Probability Score: C (Possibly a rare cause of clinically significant liver injury).

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Use during Pregnancy and Lactation
◉ Overview of Use During Lactation
A mother taking 2 grams of procainamide daily will have low concentrations of the drug and its active metabolites in her breast milk. While adverse effects on larger breastfed infants are not expected, close monitoring of the newborn may be necessary if the drug is used during lactation due to a lack of data on mothers breastfeeding while receiving procainamide treatment. If there are concerns about toxicity, measuring the infant's serum drug concentration can help rule out toxicity.
◉ Effects on breastfed infants
No published information found as of the revision date.
◉ Effects on lactation and breast milk
No published information found as of the revision date.

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Protein binding
15% to 20%

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Interaction
Studies have shown that procainamide in cats…may prolong and enhance the neuromuscular blocking effect produced by succinylcholine.

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- Plasma protein binding rate:
1. Human plasma: The plasma protein binding rate of procainamide is low, at 15-20% (balanced dialysis, human plasma), and there is no concentration-dependent binding at concentrations up to 100 μg/mL [2]
- Drug-induced lupus erythematosus (DILE):
1. Incidence and mechanism: Long-term use (>6 months) of procainamide can induce DILE in 15-30% of patients, characterized by positive antinuclear antibody (ANA), joint pain and rash. Due to prolonged drug exposure time, slow acetylation is at higher risk [2]
- Hepatotoxicity:
1. Rat studies: Intraperitoneal injection of procainamide (50 mg/kg, once daily for 7 days) increased serum ALT by 2.0 ± 0.3 times, AST by 1.8 ± 0.2 times, and was accompanied by mild hepatocellular necrosis (histological examination) [3]
- Cytotoxicity:
1. In vitro cytotoxicity: Procainamide (20 mM) reduced HeLa cell viability to 50% after 48 hours (MTT method), due to lysosomal membrane permeability and vacuolation [5]
- Hematologic toxicity:
1. Human data: Rare cases of agranulocytosis have been reported (incidence 0.2%–0.5%). During procainamide treatment, a complete blood count (CBC) should be performed weekly for the first 3 months [2]

[1]. Procainamide is a specific inhibitor of DNA methyltransferase 1. J Biol Chem. 2005;280(49):40749-40756.
[2]. Procainamide. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. https://www.ncbi.nlm.nih.gov/books/NBK557788/
[3]. A comparison of the covalent binding of clozapine, procainamide, and vesnarinone to human neutrophils in vitro and rat tissues in vitro and in vivo. Chemical research in toxicology, 2005, 18(9): 1384-1394.
[4]. Involvement of K+ channel in procainamide-induced relaxation of bovine tracheal smooth muscle[J]. European journal of pharmacology, 2000, 402(1-2): 143-149.
[5]. Massive cell vacuolization induced by organic amines such as procainamide[J]. Journal of Pharmacology and Experimental Therapeutics, 2004, 310(1): 395-406.
[6]. Reactivation of tumor suppressor genes by the cardiovascular drugs hydralazine and procainamide and their potential use in cancer therapy. Clinical Cancer Research, 2003, 9(5): 1596-1603.

Procainamide is a benzamide compound with the structure 4-aminobenzamide, where the nitrogen atom of the amide is replaced by a 2-(diethylamino)ethyl group. It is an antiarrhythmic drug used to treat cardiac arrhythmias. Procainamide acts as a sodium channel blocker, antiarrhythmia agent, and platelet aggregation inhibitor. It is a derivative of procaine, but with weaker central nervous system effects. Procainamide is an antiarrhythmic drug. Procainamide is an oral antiarrhythmic drug that has been used for over 60 years. Long-term use of procainamide is known to induce hypersensitivity reactions, autoantibody formation, and lupus-like syndromes, but rarely causes clinically significant acute liver injury. It is a class Ia antiarrhythmic drug with a structure related to procaine. See also: Procainamide hydrochloride (salt form). Drug Indications For the treatment of life-threatening ventricular arrhythmias.

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Mechanism of Action
Procainamide is a sodium channel blocker. It exerts its local anesthetic effect by stabilizing neuronal membranes by inhibiting the ion flow required for impulse initiation and conduction.
Intravenous administration…can cause a drop in blood pressure; peripheral vasodilation may result in a hypotensive response, but the decrease in systolic blood pressure may be greater than that in diastolic blood pressure. …The central nervous system effects of procainamide are not significant.

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Therapeutic Uses
Antiarrhythmic drug; platelet aggregation inhibitor
Procainamide can be used to suppress ventricular arrhythmias, including premature ventricular contractions, paroxysmal ventricular tachycardia, and ventricular fibrillation. Hydrochloride/
This drug is effective for paroxysmal atrial tachycardia, atrial flutter, atrial tachycardia, or ectopic atrial contractions. For paroxysmal atrial tachycardia, other measures and first-line drugs should be tried before using procainamide. Hydrochloride/
Procainamide has been used to treat myotonia, and its action is similar to that of quinine. For more complete data on the therapeutic uses of procainamide (out of 8), please visit the HSDB record page.

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Drug Warnings
…Use with caution. If the QRS complex widens excessively, discontinue use. Procainamide is generally well tolerated. However, it can occasionally cause serious side effects, even death. Procainamide can cause adverse reactions by acting on abnormal myocardium or correcting the arrhythmia it treats. …Procainamide…should not be used in complete atrioventricular block, and should also be used with caution in partial atrioventricular block due to the risk of cardiac arrest. Cross-sensitivity to procaine and related drugs should be anticipated. …Caution must be exercised if the patient is receiving digitalis treatment. /Hydrochloride/
Fatal agranulocytosis has been reported; frequent blood tests are necessary during long-term treatment. Syndromes similar to systemic lupus erythematosus are common reactions to long-term use and may require discontinuation of treatment…
For more complete data on drug warnings for procainamide (9 of 9), please visit the HSDB record page.
Pharmacodynamics
Procainamide is a drug used for local or regional anesthesia and can also be used to treat ventricular tachycardia occurring during cardiac procedures (such as surgery or catheterization), or during acute myocardial infarction, digitalis poisoning, or other cardiac conditions. The antiarrhythmic mechanism of procainamide appears to be similar to that of procaine and quinidine. It inhibits ventricular excitability and increases the stimulation threshold of the diastolic ventricle. However, the sinoatrial node is unaffected.
- Background and Classification:
1. Procainamide is a class Ic antiarrhythmic drug developed in the 1950s for the treatment of ventricular arrhythmias. It was later identified as a DNMT1 inhibitor, thus expanding its potential use in cancer treatment [1,2,6]
- Mechanism of action:
1. Antiarrhythmic: Blocks cardiac sodium channels, slows phase 0 depolarization and prolongs QRS duration, thereby inhibiting reentrant arrhythmias [2]
2. DNMT1 inhibition: Binds to the catalytic domain of DNMT1, preventing methyl transfer to DNA and reactivating silenced tumor suppressor genes (e.g., p16INK4a, p21) [1,6]
3. Bronchodilator: Activates Ca²⁺-activated K⁺ channels in tracheal smooth muscle, leading to hyperpolarization and relaxation (potentially for the treatment of asthma, but not yet clinically approved) [4]
- Clinical indications:
1. Approved use: Treatment of life-threatening ventricular arrhythmias (e.g., ventricular tachycardia, ventricular fibrillation) when other drugs are ineffective [2]
2. Investigational use: In combination with other epigenetic drugs (e.g., histone deacetylase inhibitors) for the treatment of breast, colon, and lung cancer with hypermethylated tumor suppressor genes [6]
- FDA Warnings:
1. Risk of drug-induced lupus erythematosus (DILE): Monitor antinuclear antibody (ANA) titers every 3 months; discontinue use if ANA is positive (>1:160) or if clinical symptoms of lupus appear [2]
2. Dose adjustment for renal function: Reduce the dose by 50% for patients with creatinine clearance of 10–30 mL/min; avoid use in patients with anuria [2]
3. QT interval prolongation: Avoid concomitant use with other QT interval prolonging drugs (e.g., sotalol) to prevent torsades de pointes [2]

C13H22CLN3O

271.79

271.145

C, 57.45; H, 8.16; Cl, 13.04; N, 15.46; O, 5.89

614-39-1

Procainamide;51-06-9

4913

White to off-white solid powder

421.8ºCat 760 mmHg

165-168 °C

208.9ºC

3.114

2

3

6

17

221

0

Cl[H].O=C(C1C([H])=C([H])C(=C([H])C=1[H])N([H])[H])N([H])C([H])([H])C([H])([H])N(C([H])([H])C([H])([H])[H])C([H])([H])C([H])([H])[H]

ABTXGJFUQRCPNH-UHFFFAOYSA-N

InChI=1S/C13H21N3O.ClH/c1-3-16(4-2)10-9-15-13(17)11-5-7-12(14)8-6-11;/h5-8H,3-4,9-10,14H2,1-2H3,(H,15,17);1H

4-amino-N-[2-(diethylamino)ethyl]benzamide;hydrochloride

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: Please store this product in a sealed and protected environment (e.g. under nitrogen), avoid exposure to moisture and light.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Solubility in Formulation 1: ≥ 3.25 mg/mL (11.96 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 32.5 mg/mL clear DMSO stock solution to 400 μL of PEG300 and mix evenly; then add 50 μL of Tween-80 to the above solution and mix evenly; then add 450 μL of normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 3.25 mg/mL (11.96 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 32.5 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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Solubility in Formulation 3: ≥ 3.25 mg/mL (11.96 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 32.5 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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Solubility in Formulation 4: 120 mg/mL (441.52 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.

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 (Please use freshly prepared in vivo formulations for optimal results.)