Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Procainamide (PA) is indicated in the treatment of premature ventricular contractions, ventricular tachycardia, atrial fibrillation, and paroxysmal atrial tachycardia. PA is contraindicated in patients with complete atrioventricular block.
PA is metabolized to an active metabolite, N-acetylprocainamide (NAPA), with metabolism controlled by genetically determined enzymes. In patients with normal renal function, fast metabolizers will have a PA:NAPA ratio <1 at 3 hours after the dose is administered. Slow acetylators (PA:NAPA ratio >2 after 3 hours) are more likely to develop a positive test for antinuclear antibodies and present with systemic lupus erythematosus-like symptoms.
Patients who have prolonged exposure to procainamide >10.0 mcg/mL or NAPA concentration >40.0 mcg/mL are very likely to exhibit symptoms of toxicity that are characterized by hypotension, ventricular fibrillation, widened QRS complex, junctional tachycardia, oliguria, confusion, nausea, and vomiting.
Renal disease, hepatic disease, cardiac failure, and states of low cardiac output reduce the metabolism and clearance of PA and NAPA.
Co-administration of histamine H2 receptor antagonists, such as cimetidine and ranitidine reduce renal clearance of PA and NAPA resulting in higher plasma concentrations of each.
Administration of a dose of 50 mg/kg will usually yield the optimal trough concentration in the range of 4.0 to 8.0 mcg/mL for procainamide and 10.0 to 20.0 mcg/mL for N-acetylprocainamide.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
No significant cautionary statements
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Therapeutic concentration: 4.0-8.0 mcg/mL
Toxic concentration: >10.0 mcg/mL
Therapeutic concentration: 10.0-20.0 mcg/mL
Toxic concentration: >40.0 mcg/mL
Clinical References Provides recommendations for further in-depth reading of a clinical nature
Myerburg RJ, Kessler KM, Kiem I, et al: Relationship between plasma levels of procainamide, suppression of premature ventricular complexes and prevention of recurrent ventricular tachycardia. Circulation 1981;64;280-290