title: Effect of xylazine and ketamine on the pharmacokinetics of alfentanil during halothane anaesthesia.
abstract: We measured plasma concentrations of alfentanil in two horses after three different randomly ordered treatments. Each horse received halothane in oxygen by mask followed by a bolus dose of alfentanil 60 micrograms kg-1 i.v., halothane in oxygen by mask followed by an i.v. alfentanil infusion for 120 min and xylazine and ketamine followed by halothane and a bolus dose of alfentanil 60 micrograms kg-1 i.v. Halothane was maintained at 1.05-1.07% end-tidal concentration with a PaCO2 of 6-7.3 kPa. The plasma concentration-time curves were similar after bolus and infusion doses of alfentanil with halothane and could be fitted to a two-compartment open model. A plateau was noted in the plasma concentration-time curve in the presence of xylazine-ketamine which could not be modelled adequately, but suggested a three-compartment open model with an additional input component.
authors.affiliation: Department of Surgery, School of Veterinary Medicine, University of California, Davis 95616-8745.
authors.forename: P J
authors.initials: PJ
authors.lastname: Pascoe
authors.forename: W D
authors.initials: WD
authors.lastname: Black
authors.forename: E P
authors.initials: EP
authors.lastname: Steffey
mesh_terms: D015760:Alfentanil / Q000097:blood / Q000493:pharmacokinetics*; D000769:Anesthesia, Inhalation / Q000662:veterinary*; D000818:Animals; D006221:Halothane; D006736:Horses / Q000378:metabolism*; D007649:Ketamine / Q000494:pharmacology*; D008954:Models, Biological; D014991:Xylazine / Q000494:pharmacology*
chemical_list: D015760:Alfentanil; D014991:Xylazine; D007649:Ketamine; D006221:Halothane