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

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Abstract
Ketamine hydrochloride was administered i.v. to unpremedicated and xylazine-treated calves [drugs used in combination for maintenance of anesthesia]. The plasma concentrations of ketamine and norketamine were measured at several time intervals after drug administration and the data were fitted to a 2-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 per kg. Premedication with xylazine, while 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 2 groups of female calves.