title: Sedative and cardiopulmonary effects of medetomidine hydrochloride and xylazine hydrochloride and their reversal with atipamezole hydrochloride in calves.
abstract: OBJECTIVE
  To assess the sedative and cardiopulmonary effects of medetomidine and xylazine and their reversal with atipamezole in calves.
  
  
  METHODS
  25 calves.
  
  
  METHODS
  A 2-phase (7-day interval) study was performed. Sedative characteristics (phase I) and cardiopulmonary effects (phase II) of medetomidine hydrochloride and xylazine hydrochloride administration followed by atipamezole hydrochloride administration were evaluated. In both phases, calves were randomly allocated to receive 1 of 4 treatments IV: medetomidine (0.03 mg/kg) followed by atipamezole (0.1 mg/kg; n = 6), xylazine (0.3 mg/kg) followed by atipamezole (0.04 mg/kg; 7), medetomidine (0.03 mg/kg) followed by saline (0.9% NaCl; 6) solution (10 mL), and xylazine (0.3 mg/kg) followed by saline solution (10 mL; 6). Atipamezole or saline solution was administered 20 minutes after the first injection. Cardiopulmonary variables were recorded at intervals for 35 minutes after medetomidine or xylazine administration.
  
  
  RESULTS
  At the doses evaluated, xylazine and medetomidine induced a similar degree of sedation in calves; however, the duration of medetomidine-associated sedation was longer. Compared with pretreatment values, heart rate, cardiac index, and PaO(2) decreased, whereas central venous pressure, PaCO(2), and pulmonary artery pressures increased with medetomidine or xylazine. Systemic arterial blood pressures and vascular resistance increased with medetomidine and decreased with xylazine. Atipamezole reversed the sedative and most of the cardiopulmonary effects of both drugs.
  
  
  CONCLUSIONS
  At these doses, xylazine and medetomidine induced similar degrees of sedation and cardiopulmonary depression in calves, although medetomidine administration resulted in increases in systemic arterial blood pressures. Atipamezole effectively reversed medetomidine- and xylazine-associated sedative and cardiopulmonary effects in calves.
authors.affiliation: Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
authors.forename: Eva
authors.initials: E
authors.lastname: Rioja
authors.forename: Carolyn L
authors.initials: CL
authors.lastname: Kerr
authors.forename: Saad S
authors.initials: SS
authors.lastname: Enouri
authors.forename: Wayne N
authors.initials: WN
authors.lastname: McDonell
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002417:Cattle / Q000502:physiology*; D004347:Drug Interactions; D006339:Heart Rate / Q000187:drug effects; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D014655:Vascular Resistance / Q000187:drug effects; D014991:Xylazine / Q000037:antagonists & inhibitors / Q000494:pharmacology*
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D006993:Hypnotics and Sedatives; D007093:Imidazoles; C050701:atipamezole; D014991:Xylazine; D020926:Medetomidine