Abstract

Dexmedetomidine is the active enantiomer of racemic medetomidine.^1,2,4 Dexmedetomidine has been used extensively in human medicine and was developed as a reversible adrenergic agonist agent with potent analgesic, anxiolytic, and sedative effects.³ Dexmedetomidine acts specifically and selectively on alpha-2-adrenoreceptors, more so than on alpha-1-adrenoreceptors at a ratio of 1600:1. Due to this high selectivity of alpha-2 receptors, dexmedetomidine offers more potent sedation and analgesia with less cardiovascular depression than alpha-1 receptor activation.^1,2

Nineteen captive cheetahs (Acinonyx jubatus) at the Cheetah Conservation Fund (CCF), Namibia were immobilized for annual examination. The cheetahs received dexmedetomidine (Dx) dosages ranging from 12.8–22.5 µg/kg (17.4±3.02 µg/kg) and ketamine (K) dosages of 4.2–5.9 mg/kg (5.01±0.56 mg/kg) given intramuscularly. Sedation, analgesia and muscle relaxation were rated subjectively. Temperature, heart rate, respiratory rate, end-tidal CO₂ and indirect blood pressure were measured every 5 min for 1 h. Blood gas analysis was done within the first 15 min after initial injection. After 1 h, the cheetahs were placed on isoflurane by endotracheal tube. At the end of each procedure the sedative effect was reversed using a dose of atipamezole administered intramuscularly at 10 times the initial dose of dexmedetomidine

The combination of dexmedetomidine/ketamine produced a fast and smooth induction with excellent sedation level for minor procedures and transportation. Although the cardiovascular parameters were similar to those observed with medetomidine (M) and ketamine (K) combinations, the mean heart rate with the Dx/K combination was slightly higher than M/K, but the difference was not statistically significant. Two cheetahs showed marked bradycardia and few individuals experienced ventricular premature contractions as noted on the ECG. The dose of isoflurane needed for anesthesia maintenance was half the dose of isoflurane used for the maintenance of cheetahs induced with a medetomidine/ketamine combination. Recoveries were subjectively faster with the dexmedetomidine combination compared with M/K.

Dexmedetomidine, in combination with ketamine, is a safe alternative for the immobilization of captive cheetahs. Although the cardiorespiratory and clinical effects of dexmedetomidine did not differ significantly from M/K combinations, less bradycardic effects and the shorter recovery times make use of this combination more suitable than M/K combinations.

Acknowledgments

The authors would like to thank Dr. Francisco Rodriguez, Leigh Pitsko, and Marianne De Jonge for their assistance during the immobilizations. Thanks also to the numerous volunteers at the CCF for their help during the annual examinations of the cheetahs.

Literature Cited

1.  Kuusela, E. 2004. Dexmedetomidine and levomedetomidine, the isomers of medetomidine in dogs. Academic dissertation. Univ. of Helsinki, Helsinki, Finland.

2.  Kuusela, E., M. Raekallio, and O. Vainio. 2000. Comparison of three doses of dexmedetomidine and its enantiomers in dogs. J. Vet. Pharmacol. Ther. 23:15–20.

3.  Mantz, J. 1999. Dexmedetomidine. Drugs of Today. 35:151–157.

4.  Selmi, A.L., M.M. Guilherme, B.T. Lins, J.P. Figueiredo, and G.R. Barbudo-Selmi. 2003. Evaluation of the sedative and cardiorespiratory effects of dexmedetomidine, dexmedetomidine-butorphanol, and dexmedetomidine-ketamine in cats. J. Am. Vet. Med. Assoc. 222:37–41.