Randomised, blinded clinical trial comparing dogs’ sedation scores following methadone–medetomidine injection at Governing Vessel 20, the epaxial lumbar muscles or the quadriceps muscles

BACKGROUND: Intramuscular injection of sedatives into different muscles may affect the quality of sedation. Subcutaneous injection is less painful but has a less predictable effect; however, administration at Governing Vessel 20 (GV20) may improve sedation. METHODS: Seventy-three dogs were premedicated with medetomidine and methadone. The route of administration was determined by random allocation: subcutaneous injection at GV20 (GV-20), intramuscular injection into the quadriceps muscles (IM-Q) or intramuscular injection into the epaxial lumbar muscles (IM-L). Sedation was scored at 3, 7 and 10 minutes after injection using a simple descriptive scale. RESULTS: Scores were higher in groups IM-Q and GV-20 than in group IM-L and did not differ significantly between GV-20 and IM-Q at any time point. Scores differed significantly between IM-L and IM-Q at 3 minutes, between IM-L and both IM-Q and GV-20 at 7 minutes, and between GV-20 and IM-L at 10 minutes. LIMITATIONS: Differences in patient size between groups, inter-rater variability and the use of allometric dosing may have affected the results. CONCLUSIONS: The quality of sedation following injection of methadone and medetomidine at GV20 does not differ significantly from that following injection into the quadriceps muscles, and the injection is well tolerated. Injection into the epaxial lumbar muscles results in less profound sedation, possibly because of inadvertent subcutaneous injection or anatomical differences in tissue perfusion.