The pharmacokinetics of ketamine administered intravenously in calves and the modifying effect of premedication with xylazine hydrochloride.

Ketamine hydrochloride was administered intravenously to unpremedicated and xylazine-treated calves. The plasma concentrations of ketamine and norketamine were measured at several time intervals after drug administration and the data were fitted to a two-compartment open model. In unpremedicated female calves the distribution and elimination half-lives averaged 6.9 and 60.5 min, respectively. The volume of the central compartment was 1.21 l/kg and the peripheral compartment was 4.04 l/kg. Total body clearance of ketamine averaged 40.4 ml/min/kg. Premedication with xylazine, whilst not affecting the half-lives significantly, reduced volumes of distribution and the clearance rate of the drug by approximately 50%. The results for the male calves which were premedicated were intermediate between the two groups of female calves.