title: The effects of medetomidine on the action of vecuronium in dogs anaesthetized with halothane and nitrous oxide.
abstract: OBJECTIVE
  To quantify the effects of medetomidine on the onset and duration of vecuronium-induced neuromuscular blockade in dogs.
  
  
  METHODS
  Randomized, prospective clinical study.
  
  
  METHODS
  Twenty-four, healthy, client-owned dogs of different breeds, aged between 6 months and 10 years and weighing between 5.0 and 40.0 kg undergoing elective surgery.
  
  
  METHODS
  Dogs were randomly allocated to two groups. Pre-anaesthetic medication in group M+ was intramuscular acepromazine (ACP) 25 microg kg(-1), morphine 0.5 mg kg(-1) and medetomidine 5 microg kg(-1). Group M- received ACP and morphine only, at the same dose rate. After induction with thiopental, anaesthesia was maintained with halothane in oxygen and nitrous oxide. End-tidal halothane concentration was maintained at 1.1%. Neuromuscular blockade was produced with intravenous vecuronium (50 microg kg(-1)) and monitored using a train of four stimulus applied at the ulnar nerve. The times taken for loss and reappearance of the four evoked responses (twitches [T]) were recorded. Normal and nonparametric data were analysed with an independent t-test and Mann-Whitney's U-test, respectively.
  
  
  RESULTS
  The fourth twitch (T4) disappeared at similar times in each group: 107 +/- 19; [72-132] (mean +/- SD; [range]) seconds in M+ and 98 +/- 17 [72-120] seconds in M- dogs. The first twitch (T1) was lost at 116 +/- 15; [96-132] seconds in group M+ and 109 +/- 19; [72-132] seconds in M-. The fourth twitch returned significantly earlier in M+ dogs: 20.8 +/- 3.8 [14-28] minutes compared with 23.8 +/- 2.7 [20-27] minutes (p = 0.032). The duration of drug effect (T4 absent) was significantly shorter (p = 0.027) in M+ (18.9 +/- 3.7 minutes) compared with M- dogs (22.2 +/- 2.9 minutes). The recovery rate (interval between reappearance of T1 and T4) was significantly more rapid (p = 0.0003) in medetomidine recipients (3.0 +/- 1.2 versus 5.2 +/- 1.3 minutes).
  
  
  CONCLUSIONS
  Medetomidine 5 microg kg(-1) as pre-anaesthetic medication shortened the duration of effect of vecuronium in halothane-anaesthetized dogs and accelerated recovery, but did not affect the onset time. These changes are of limited clinical significance.
authors.affiliation: Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
authors.forename: Asadollah
authors.initials: A
authors.lastname: Kariman
authors.forename: R Eddie
authors.initials: RE
authors.lastname: Clutton
mesh_terms: D018712:Analgesics, Non-Narcotic / Q000008:administration & dosage / Q000494:pharmacology; D000758:Anesthesia / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D004285:Dogs; D004347:Drug Interactions; D005260:Female; D006221:Halothane / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage / Q000494:pharmacology; D009609:Nitrous Oxide / Q000008:administration & dosage / Q000494:pharmacology*; D014673:Vecuronium Bromide / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D018712:Analgesics, Non-Narcotic; D018685:Anesthetics, Inhalation; D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide; D009609:Nitrous Oxide; D020926:Medetomidine; D006221:Halothane