Procainamide in the dog: antiarrhythmic plasma concentrations after intravenous administration

Pharmacokinetic evaluation of a sustained-release compounded procainamide preparation after 24-h (acute) administration in normal dogs

INTRODUCTION

The objective of the present study was to evaluate the pharmacokinetics of a compounded sustained-release procainamide formulation in normal dogs.

ANIMALS

Six healthy, purpose-bred mixed-breed dogs participated in the study.

METHODS

In phase I, two dogs were administered oral procainamide (30 mg/kg), and plasma was obtained to determine plasma concentration ranges and duration. In phase II, six dogs were administered procainamide (30 mg/kg by mouth every 12 hours) to determine the pharmacokinetics of sustained-release procainamide. Serum procainamide concentration was determined using an immunochemistry assay.

RESULTS

No adverse clinical effects were noted in any of the dogs studied. The average maximum serum concentration, average serum concentration, and average minimum serum concentration were 10.17, 7.13, and 3.07 μg/mL, respectively. The average time over a 12-h period during which procainamide concentration exceeded 12 μg/mL was 2.35 h, was between 4 and 12 μg/mL was 7.19 h, and was less than 4 μg/mL was 2.46 h. The average times at maximum concentration and minimum concentration were 18.67 and 12.25 h, respectively.

CONCLUSIONS

Administration of sustained-release procainamide twice daily achieved targeted plasma concentrations in most dogs. Evaluation of serum trough concentrations should be considered owing to interanimal variability to confirm that serum concentrations are within the reported therapeutic range for an individual patient.

Comparison of Acute Hemodynamic Effects of Lidocaine and Procainamide for Postoperative Ventricular Arrhythmias in Dogs

Heart rate and systolic, diastolic, and mean pressures were measured in two groups of dogs during treatment of postoperative ventricular arrhythmias either with intravenous (IV) 2% lidocaine hydrochloride or procainamide hydrochloride. Hemodynamic parameters were not significantly changed after IV administration of either drug. Additionally, changes in hemodynamic parameters for dogs treated with 2% lidocaine were not significantly different from those of dogs treated with procainamide. When dosed appropriately in the clinical setting, one bolus of IV procainamide was safe for the treatment of postoperative ventricular arrhythmias.

The pharmacokinetics and pharmacodynamics of procainamide in horses after intravenous administration

Six horses were administered either 15 or 20 mg/kg body weight (b.w.) procainamide (PA) as an intravenous (i.v.) dose over 10 min. The plasma concentrations of PA and N-acetylprocainamide (NAPA) as well as the pharmacodynamic effect (prolongation of the QT interval) were monitored. The PA plasma concentrations could be described by a one-compartment model with a t1/2 of 3.49 +/- 0.61 h. The total body clearance of PA was 0.395 +/- 0.090 l/hr/kg and the volume of distribution was 1.93 +/- 0.27 l/kg. As observed after PA administration, NAPA (an active metabolite) had a t1/2 longer than PA of 6.31 +/- 1.49 h. Peak NAPA concentrations (1.91 +/- 0.51 micrograms/ml) occurred at 5.2 h after the PA i.v. dose. The ratio of area under the curves for NAPA to PA was 0.46 +/- 0.15 which is similar to that expected in humans classified as slow acetylators. Percentage change in the QT interval was examined with respect to PA and PA + NAPA plasma concentrations. For PA, % delta QT = 41.2 log (PA) - 13.26 and correlations (r) ranged from 0.77 to 0.91 among the horses. In the case of PA+ NAPA, % delta QT = 57.3 log (PA + NAPA) - 31.83 and ranged from 0.77 to 0.90. No evidence of toxicity was noted with respect to changes in the PR interval.

Drug interactions

Drug interactions are often the result of complex biochemical, physical, and kinetic factors and may not often be easily predicted or even recognized. Although this article has attempted to point out the more common mechanisms and results of drug interactions, the few interactions that have been documented in small animals are undoubtedly only the tip of the iceberg. For the safety of patients and for the highest quality of veterinary care, it is essential that the practitioner become thoroughly familiar with the actions and interactions of drugs used in his or her practice and realize the possible consequences of multiple drug therapies before adding another drug to a therapeutic regimen. From a therapeutics standpoint, the temptation to polypharmacy is great, but the adage "an ounce of prevention is worth a pound of cure" is especially appropriate when discussing drug therapy. The rational decision to use as few drugs as possible in any given situation is the route to safe and successful drug therapy.