Procainamide Level

Procainamide is a class 1a antiarrhythmic that is used to treat various ventricular and atrial arrhythmias. Procainamide and its breakdown product, N-acetylprocainamide (NAPA), are both powerful antiarrhythmics that necessitate careful monitoring. ^[1]

The therapeutic concentration of procainamide is 4-8 µg/mL. The half-life is 3-5 hours. The toxic concentration is 16 µg/mL or greater, although symptoms may develop at 8-10 µg/mL.

The therapeutic concentration of NAPA is also 4-8 µg/mL, and its half-life is approximately 7 hours. As with procainamide, the toxic concentration of NAPA is 16 µg/mL or greater, although symptoms may develop at 8-10 µg/mL.

The therapeutic concentration of both procainamide and N-acetylprocainamide (combined) is 30 µg/mL or less. The toxic concentration is any level in excess of the therapeutic concentration (≥30 µg/mL).

When procainamide levels become supratherapeutic, the risk of the drug’s side effects becomes increased (see Background). Levels of both procainamide and NAPA are typically checked before the administration of the second dose. Toxicity may occur when levels of either or the combination of both are too high (see Reference Range).

Signs and symptoms of toxicity include confusion, dizziness, drowsiness, decreased urination, nausea, vomiting, hypotension, tachycardia, and arrhythmias.

See the list below:

• Specimen: Blood

• Container: Red-top tube

• Minimum: 0.4 mL

• Method: Routine venipuncture

Description

Procainamide hydrochloride is a class 1a antiarrhythmic that is used to treat a wide variety of ventricular and atrial arrhythmias. Its mechanism of action is to decrease myocardial excitability, to slow conduction velocities, and to depress myocardial contractility.

Procainamide is converted by the liver to its breakdown product N-acetylprocainamide (NAPA), which is also an active antiarrhythmic compound. The remainder (approximately 35%-65%) is excreted unchanged by the kidneys. When the level of procainamide or NAPA becomes supratherapeutic, the risk of the drug’s side effects becomes increased. levels are typically checked before the administration of the second dose.

Serious side effects of procainamide include seizures, asystole, heart block, ventricular arrhythmias, and agranulocytosis

Other side effects include confusion, dizziness, hypotension, diarrhea, anorexia, bitter taste, nausea, vomiting, rash, eosinophilia, leukopenia, thrombocytopenia, chills, drug-induced systemic lupus syndrome, and fever. ^[2]

Indications/Applications

Some indications for the use of procainamide include atrial premature contractions, premature ventricular contractions, ventricular tachycardia, paroxysmal atrial tachycardia, and maintenance of a normal sinus rhythm after conversion from atrial fibrillation/flutter (AF)

When procainamide is given in a hospital setting, it is typically given either intravenously or intramuscularly. When given intravenously, the patient’s ECG, blood pressure, and pulse should be monitored. In addition, the patient should remain supine to minimize hypotension.

A study by Matuskowitz et al found that in emergency department (ED) patients presenting with recent-onset AF, that is, AF of less than 48 hours’ duration, a 60.9% cardioversion rate was achieved in those who underwent procainamide treatment. The mean intravenous procainamide dose given was 1062.4 mg (12.1 mg/kg). The investigators reported that 25.6% of the patients who achieved cardioversion with procainamide were admitted to the hospital, compared with 52.0% of the other study patients. However, the 30-day return rate to the ED did not significantly differ between the two groups. The most frequent adverse event in the procainamide patients was transient hypotension. ^[3]

Considerations

Laboratory abnormalities such as increased levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, lactate dehydrogenase (LDH), bilirubin, and antinuclear antibody (ANA) and a positive Coombs test may result.

Complete blood cell counts should be monitored every 2 weeks in the first 3 months of use to assess for any signs of agranulocytosis. Procainamide should be discontinued if leukopenia is noted. In the cases of prolonged use, ANA titers should be monitored periodically to assess for drug-induced lupus and discontinued if steady increase in ANA is noted.

Contraindications

Procainamide is contraindicated in conditions with preexisting QT prolongation, torsade de pointes, second- or third-degree heart block without pace maker placement, or history of hypersensitivity reaction to procainamide. Special consideration should be taken with conditions such as myasthenia gravis or systemic lupus erythematosus.