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Abstract |
The recent development of potent and specifica lphar-adrenoceptoar gonistsa nd antagonists has enhanced their use in nondomestic animal immobilization and reversal. Medetomidine, a new potent alphar-agonist, in combination with the dissociative anesthetic ketamine, has been used to immobilize a variety of nondomestic mammals. Medetomidine alone induces sedation in a dose-dependent way, and complete immobilization has been achieved with high doses in semidomesticated reindeer (Rangifer tarandus) and blue foxes (Alopex lagopus). Howbver, we feel that ketamine should be added to the immobilization mixture to ensure complete immobilization and operator safety. In ketamine combinations, medetomidine doses are usually 60-100 pg/kg. The required ketamine doses are remarkably low:0.8-1.6 mglkg in most ruminants,2.5-3.0 mgUgin felids,u rsids,a nd canids,a nd 5.G-8.0m glkgi n primates,w olverines(Gulog ulo),ando therm uitelids. Clinically, the resulting immobilization is characterized by a smooth onset, good to excellent myorelaxation, and areflexia at higher doses. Determinations of hematologic, serum biochemicil, arterial blood gas,a nd acid-bases tatusp arametersi ndicate that the immobilization is physiologically sound. We have had no fatalities attributable to the immobilization mixture ( I ,240 immobilizations). The alphar-adrenoceptora ntagonist,a tipamezole,i s highly efective in reversingt he immobilization induced by medetomidine, medetomidine-ketamine combinations, or xylazine. In ruminants, the medetomidine-ketamine-induced immobilization can be rapidly and persistently reversed by administering 100-l 50 1rg/kg of alipamezole i.v. and the rest s.c., adjusting the total atipamezole dose to an atipamezole: medetomidine ratio of approximately 4-5 (w/w). Becauseth e required ketamine doses are relatively high in carnivores, we prefer to use a lower atipamezole dose (totil atipamezoie: medetomidine ratio approximately 2-3 w/w) and to administer it i.m. or s.c. Using thii regimen, reversals are calm and animals show minimal “residual ketamine effect.” Because atipamezole is a competitive antagonist, its dose should be reduced if it is administered late in the immobilization period when a large part of medetomidine has been endogenously metabolized. Xylazine-induced immobilization is rapidly reversed by I mg of atipamezole for every 8-12 mg of xylazine used. |
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