Pharmacokinetics of ketamine in the horse.

Ketamine HCl was administered IV to xylazine HCl-treated horses. The plasma concentration of ketamine was measured several times after administration of the drug and these data were used to develop a two-compartment pharmacokinetic model. The distribution and the elimination phase half-lives averaged 2.9 and 42 minutes. The volume of the central compartment averaged 212 ml/kg of body weight and the volume of the peripheral compartment was approximately threefold larger. The total body clearance of ketamine averaged 26.6 ml/minute/kg. Plasma protein binding of ketamine averaged 50% over the concentration limits of 0.3 to 20 microgram/ml. The duration of anesthesia from a single 2.2 mg/kg IV bolus dose of ketamine HCl appeared to be determined largely by distribution; 40% of this dose was predicted to remain in the horse at the time of its recovery from anesthesia.