Procainamide pharmacokinetics in beagles: urinary pH dependency and comparison with n-acetylprocainamide

Area of Science:

• Pharmacology
• Renal Physiology
• Drug Metabolism

Background:

• Procainamide (PA) is an antiarrhythmic drug with variable renal excretion.
• Understanding PA pharmacokinetics is crucial for optimizing therapeutic efficacy and safety.
• Urinary pH is a known factor influencing the excretion of weak bases and acids.

Purpose of the Study:

• To investigate the pharmacokinetic behavior of procainamide (PA) in beagles.
• To determine the influence of urinary pH on the renal excretion of PA.
• To compare the pharmacokinetic profiles of PA and its metabolite, N-acetylprocainamide (NAPA).

Main Methods:

• Intravenous (i.v.) bolus injections of procainamide (PA) were administered to male and female beagles.
• Urine samples were collected to assess the effect of urinary pH on renal excretion.
• N-acetylprocainamide (NAPA) was administered in a crossover study to compare its pharmacokinetics with PA.
• Acid hydrolysis was performed on urine samples to detect hydrolyzable substances.

Main Results:

• Urinary alkalinization increased PA plasma disappearance half-life (t1/2) and decreased renal clearance (ClR) and total body clearance (ClB).
• The apparent volume of distribution for PA remained unchanged despite changes in urinary pH.
• Acid hydrolysis of urine revealed a 17% increase in measured PA, indicating a previously unrecognized hydrolyzable substance.
• N-acetylprocainamide (NAPA) exhibited a longer t1/2 and lower ClR and ClB values compared to PA.

Conclusions:

• Urinary pH significantly modulates procainamide (PA) pharmacokinetics, affecting its elimination half-life and clearance.
• A novel hydrolyzable substance in beagle urine, distinct from N-acetylprocainamide (NAPA), influences PA measurements.
• Both PA and NAPA share similar dependencies on renal and non-renal clearance mechanisms, but NAPA demonstrates prolonged elimination.