The effects of medetomidine on the action of vecuronium in dogs anaesthetized with halothane and nitrous oxide.
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.
Kariman
Asadollah
A
Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran.
Clutton
R Eddie
RE
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*
D018712:Analgesics, Non-Narcotic; D018685:Anesthetics, Inhalation; D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide; D009609:Nitrous Oxide; D020926:Medetomidine; D006221:Halothane