title: Pharmacokinetics and pharmacodynamics of butorphanol following intravenous administration to the horse.
abstract: Butorphanol is a narcotic analgesic commonly used in horses. Currently, any detectable concentration of butorphanol in biological samples collected from performance horses is considered a violation. The primary goal of the study reported here was to update the pharmacokinetics of butorphanol following intravenous administration, utilizing a highly sensitive liquid chromatography-mass spectrometry (LC-MS) assay that is currently employed in many drug-testing laboratories. An additional objective was to characterize behavioral and cardiac effects following administration of butorphanol. Ten exercised adult horses received a single intravenous dose of 0.1 mg/kg butorphanol. Blood and urine samples were collected at time 0 and at various times for up to 120 h and analyzed using LC-MS. Mean±SD systemic clearance, steady-state volume of distribution, and terminal elimination half-life were 11.5±2.5 mL/min/kg, 1.4±0.3 L/kg, and 5.9±1.5 h, respectively. Butorphanol plasma concentrations were below the limit of detection (LOD) (0.01 ng/mL) by 48 h post administration. Urine butorphanol concentrations were below the LOD (0.05 ng/mL) of the assay in seven of 10 horses by 120 h post drug administration. Following administration, horses appeared excited as noted by an increase in heart rate and locomotion. Gastrointestinal sounds were markedly decreased for up to 24 h.
authors.affiliation: K.L. Maddy Equine Analytical Chemistry Laboratory, School of Veterinary Medicine, University of California, Davis, CA 95616, USA. hkknych@ucdavis.edu
authors.forename: H K
authors.initials: HK
authors.lastname: Knych
authors.forename: H C
authors.initials: HC
authors.lastname: Casbeer
authors.forename: D S
authors.initials: DS
authors.lastname: McKemie
authors.forename: R M
authors.initials: RM
authors.lastname: Arthur
mesh_terms: D000818:Animals; D002077:Butorphanol / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology / Q000652:urine; D002319:Cardiovascular System / Q000187:drug effects; D002853:Chromatography, Liquid / Q000662:veterinary; D005260:Female; D006207:Half-Life; D006736:Horses / Q000097:blood / Q000652:urine; D007275:Injections, Intravenous / Q000662:veterinary; D008297:Male; D013058:Mass Spectrometry / Q000662:veterinary; D009043:Motor Activity / Q000187:drug effects; D009294:Narcotics / Q000008:administration & dosage / Q000097:blood / Q000493:pharmacokinetics* / Q000494:pharmacology / Q000652:urine
chemical_list: D009294:Narcotics; D002077:Butorphanol