title: Comparison of the effects of the alpha-2 agonists detomidine, romifidine and xylazine on nociceptive withdrawal reflex and temporal summation in horses.
abstract: OBJECTIVE
  To evaluate and compare the antinociceptive effects of the three alpha-2 agonists, detomidine, romifidine and xylazine at doses considered equipotent for sedation, using the nociceptive withdrawal reflex (NWR) and temporal summation model in standing horses.
  
  
  METHODS
  Prospective, blinded, randomized cross-over study.
  
  
  METHODS
  Ten healthy adult horses weighing 527-645 kg and aged 11-21 years old.
  
  
  METHODS
  Electrical stimulation was applied to the digital nerves to evoke NWR and temporal summation in the left thoracic limb and pelvic limb of each horse. Electromyographic reflex activity was recorded from the common digital extensor and the cranial tibial muscles. After baseline measurements a single bolus dose of detomidine, 0.02 mg kg(-1), romifidine 0.08 mg kg(-1), or xylazine, 1 mg kg(-1), was administered intravenously (IV). Determinations of NWR and temporal summation thresholds were repeated at 10, 20, 30, 40, 60, 70, 90, 100, 120 and 130 minutes after test-drug administration alternating the thoracic limb and the pelvic limb. Depth of sedation was assessed before measurements at each time point. Behavioural reaction was observed and recorded following each stimulation.
  
  
  RESULTS
  The administration of detomidine, romifidine and xylazine significantly increased the current intensities necessary to evoke NWR and temporal summation in thoracic limbs and pelvic limbs of all horses compared with baseline. Xylazine increased NWR thresholds over baseline values for 60 minutes, while detomidine and romifidine increased NWR thresholds over baseline for 100 and 120 minutes, respectively. Temporal summation thresholds were significantly increased for 40, 70 and 130 minutes after xylazine, detomidine and romifidine, respectively.
  
  
  CONCLUSIONS
  Detomidine, romifidine and xylazine, administered IV at doses considered equipotent for sedation, significantly increased NWR and temporal summation thresholds, used as a measure of antinociceptive activity. The extent of maximal increase of NWR and temporal summation thresholds was comparable, while the duration of action was drug-specific.
authors.affiliation: Anaesthesiology Section, Department of Veterinary Sciences, Vetsuisse Faculty, University of Bern, Bern, Switzerland. helene.rohrbach@knp.unibe.ch
authors.forename: Helene
authors.initials: H
authors.lastname: Rohrbach
authors.forename: Toni
authors.initials: T
authors.lastname: Korpivaara
authors.forename: Urs
authors.initials: U
authors.lastname: Schatzmann
authors.forename: Claudia
authors.initials: C
authors.lastname: Spadavecchia
mesh_terms: D000818:Animals; D018592:Cross-Over Studies; D005260:Female; D005552:Forelimb; D006614:Hindlimb; D006736:Horses; D007093:Imidazoles / Q000494:pharmacology*; D008297:Male; D010146:Pain / Q000188:drug therapy / Q000662:veterinary*; D012018:Reflex; D013997:Time Factors; D014991:Xylazine / Q000494:pharmacology*
chemical_list: D007093:Imidazoles; D014991:Xylazine; C041255:detomidine; C076257:romifidine