Pharmacokinetics, bioavailability, and dosage regimens of digoxin in the horse and dog

Abstract

The purpose of this investigation was: i) to determine the pharmacokinetics and bioavailability of digoxin in horses and dogs. ii) to calculate digoxin dosage regimens using the data collected. iii) to verify pharmacokinetically derived digoxin dosage regimens in horses and dogs. Six normal adult horses and dogs were given digoxin (30 ug/kg) intravenously, and, on different occasions, orally. Multiple plasma samples were collected over 73 hours (horses) and 60 hours (dogs) for subsequent radioimmunoassay of digoxin levels. In both species the mean plasma digoxin versus time profile was triexponential. In horses two distributive phases with half lives of 15 minutes and 4.08 hours were followed by an eliminative phase with a half life of 23.10 hours. Corresponding times in dogs were 9 minutes, 4.71 and 30.13 hours. Volumes of distribution by extrapolation were 6.79 and 15.63 1/kg for horses and dogs respectively. Using the area method, corresponding results were 4.89 and 12.43 1/kg. In horses, digoxin in the form of powdered tablets suspended in water, administered intragastrically, was rapidly but incompletely absorbed (bioavailability 19.2%). In dogs the elixir was rapidly and relatively well absorbed (bioavailability 68.5%, whereas absorption was delayed and less complete than the elixir (bioavailability 49.5%). ...