Evaluation of Intramuscular Alfaxalone for Induction of Anesthesia in Clinical Reptile Cases
Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland
Alfaxalone is a neurosteroid anaesthetic that binds to γ-aminobutyric acid cell surface receptors. Alfaxalone is highly insoluble in water and historically was formulated in combination with alfadolone and the solubilising agent Cremophor EL. A new formulation of alfaxalone, solubilised in cyclodextrin, has been used to induce anaesthesia in a variety of reptile species.1-3
Alfaxalone was injected IM at a dose of 10–30 mg/kg in 6 snakes, 15 lizards and 16 chelonians. The animals weighed 20–4180 g and general condition prior to anesthesia ranged from good to poor. Anesthesia was required for various surgical and diagnostic reasons. Mean induction time was 19 min (range 3–40 min). Six animals achieved deep sedation, 21 light anesthesia and 4 surgical anesthesia. Differences in immobilization levels were seen between species; higher doses of alfaxalone were required in Hermann’s tortoises in comparison to sliders to achieve similar levels of immobilization. Two cases showed apnea 5–10 minutes after administration of alfaxalone. Supplemental isoflurane to perform surgery was administered as required in 46% of the cases and, of these, 84% were manually ventilated. Mean time to regaining spontaneous ventilation after discontinuation of isoflurane was 17 minutes (5–60 min). Recovery from anesthesia was smooth. Two geckos, both presenting in poor general condition and requiring surgery due to dystocia, died in the postoperative phase.
In conclusion, alfaxalone in its new formulation is a reliable agent in lizards, turtles and snakes to induce sedation or anesthesia. The level and duration of immobilization is dose- and species dependent. Respiratory depression may occur and the anesthetist should be prepared to intubate the reptile’s trachea. Due to its dilute concentration, the injection volume of alfaxalone for IM dosages is fairly large in comparison to other anesthetics.
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