Dexmedetomidine or medetomidine: which should veterinary surgeons select?

Medetomidine, an alpha2-adrenoceptor agonist, is a racemic mixture of two optical stereoisomers: dexmedetomidine (the active enantiomer) and levomedetomidine. Both medetomidine and dexmedetomidine are authorised for use in cats and dogs in the UK. Dexmedetomidine may offer some therapeutic benefits when compared with the racemic mixture. This article reviews some of the current literature on these two drugs, to assess whether dexmedetomidine should be used in preference to medetomidine. Studies have compared the efficacy of the active enantiomer with the racemate in dogs and cats. In dogs, at doses considered to be equipotent, the sedative scores and analgesic effects could not be distinguished following intravenous administration. Following intramuscular (IM) administration, medetomidine was faster in onset and the magnitude of effect was also greater than that obtained with dexmedetomidine. In cats, IM medetomidine had a tendency to produce higher sedation scores and a greater level of analgesia. When administered as part of the ‘cat quad’ protocol for castration, there were no significant differences in sedative effects, but cats receiving dexmedetomidine were able to stand earlier. Atipamezole was equally effective in reversal of dexmedetomidine and medetomidine. Duration of action is shorter following administration of dexmedetomidine. Differences in efficacy are dependent on the route of administration. This information may be useful to clinicians when choosing which one of these drugs to use clinically.