Evaluation of the muscular relaxant effect of dexmedetomidine or medetomidine in cats

The alpha2 adrenoceptor agonist medetomidine (MED) is an equal racemic mixture of two enantiomers, dexmedetomidine (DEX) and levomedetomidine (LEV); the LEV enantiomer is generally considered to be pharmacologically inactive, whereas the DEX enantiomer is active (Virtanen et al., 1988; MacDonald et al., 1991; Savola et al., 1991). Clinical studies in dogs and cats have shown that the pharmacodynamic effects of DEX are twice as potent as MED racemic mixture, therefore DEX administered at half the dose compared with MED for sedation; such as MED, DEX sedative and analgesic effects are antagonised by atipamezole (Cullen et al., 1996; Ansah et al., 1998; Kuusela et al., 2000; Ansah et al., 2000; Mendes et al., 2003; Granholm et al., 2006). DEX has been approved in Italy for clinical use in dogs and cats since 2008, and immediately we started to use it for dog and cat sedation. The DEX sedation effect in the dog is looked like MED, whereas the muscular relaxant effect in the cat was lower than MED. The aim of this study was to evaluate and compare the muscular relaxant effects in cats following DEX or MED used at bioequivalent dose.