title: Cardiorespiratory, gastrointestinal, and analgesic effects of morphine sulfate in conscious healthy horses.
abstract: OBJECTIVE
  To compare the cardiorespiratory, gastrointestinal, analgesic, and behavioral effects between IV and IM administration of morphine in conscious horses with no signs of pain.
  
  
  METHODS
  6 healthy adult horses.
  
  
  METHODS
  Horses received saline (0.9% NaCl) solution (IM or IV) or morphine sulfate (0.05 and 0.1 mg/kg, IM or IV) in a randomized, masked crossover study design. The following variables were measured before and for 360 minutes after drug administration: heart and respiratory rates; systolic, diastolic, and mean arterial blood pressures; rectal temperature; arterial pH and blood gas variables; intestinal motility; and response to thermal and electrical noxious stimuli. Adverse effects and horse behavior were also recorded. Plasma concentrations of morphine, morphine-3-glucuronide, and morphine-6-glucuronide were measured via liquid chromatography-mass spectrometry.
  
  
  RESULTS
  No significant differences in any variable were evident after saline solution administration. Intravenous and IM administration of morphine resulted in minimal and short-term cardiorespiratory, intestinal motility, and behavioral changes. A decrease in gastrointestinal motility was detected 1 to 2 hours after IM administration of morphine at doses of 0.05 and 0.1 mg/kg and after IV administration of morphine at a dose of 0.1 mg/kg. Morphine administration yielded no change in any horse's response to noxious stimuli. Both morphine-3-glucuronide and morphine-6-glucuronide were detected in plasma after IV and IM administration of morphine.
  
  
  CONCLUSIONS
  Clinically relevant doses of morphine sulfate yielded minimal and short-term behavioral and intestinal motility effects in healthy horses with no signs of pain. Neither dose of morphine affected their response to a noxious stimulus.
authors.affiliation: Department of Small Animal Medicine and Surgery, School of Veterinary Medicine, St George's University, Grenada, West Indies. jfigueir@sgu.edu
authors.forename: Juliana P
authors.initials: JP
authors.lastname: Figueiredo
authors.forename: William W
authors.initials: WW
authors.lastname: Muir
authors.forename: Richard
authors.initials: R
authors.lastname: Sams
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001831:Body Temperature; D018592:Cross-Over Studies; D005769:Gastrointestinal Motility / Q000187:drug effects*; D006339:Heart Rate; D006736:Horses; D007273:Injections, Intramuscular / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D009020:Morphine / Q000008:administration & dosage / Q000494:pharmacology*; D009022:Morphine Derivatives / Q000097:blood; D009043:Motor Activity / Q000187:drug effects*; D017288:Pain Threshold / Q000187:drug effects*; D056152:Respiratory Rate
chemical_list: D009022:Morphine Derivatives; C035349:morphine-6-glucuronide; D009020:Morphine; C018108:morphine-3-glucuronide