Pharmacokinetics of peniobarbital in the cat and comparisons with the rabbit and man

In eight experiments involving four cats, doses of 12.5 to 50 mg of sodium pentobarbital per kg of body weight were administered intravenously and pentobarbital plasma concentrations (from arterial blood) were measured as a function of time. Pharmacokinetic linearity was evidenced by a mean plasma clearance (C1p) of 1.81 ml/(kg x min), with a coefficient of variation of 16.6%, and a range of 1.51 to 2.36 for all experiments, and, a linear relationship between total area under the curve (AUC) and mg/kg dose in cat "4 given doses of 12.5, 25 and 50 mg/kg. However, the apparent elimination half-life, (t1/2)beta' averaged 4.87 hr, with a coefficient of variation of 40.7%, and range of 1.80 to 7.52 in all experiments, and, in cat "4 the half-life was the same, namely 7.5 hr following the two higher doses, but lower, namely 4.7 hr, after the lowest dose. There was also evidence of kinetic nonlinearity in the intial fall-off portions of some of the curves. Results are compared with literature data for both rabbits anamen. The order of plasma clearances in units of ml/(kg x min) were: rabbit greater than cat greater than man. For neither the rabbit nor the cat were there any significant correlations between calculated pharmacokinetic parameters and mg/kg doses using data from all animals studied; this also suggests kinetic linearity.