Australian Wildlife Heath Centre, Healesville Sanctuary, Zoos Victoria, ... All animals examined were captive-born, healthy, and had no history of chronic illness.
A Preliminary Investigation into the Chemical Restraint with Alfaxalone of Selected Australian Squamate Species T. Franciscus Scheelings1,2, BVSc, MVSc, MACVSc, Rupert T. Baker1, BVSc, MACVSc, Gerry Hammersley1, BSc, RVN, Kim Hollis1, RVN, Ian Elton1, Cert III (Zoo Keep), Peter Holz1, BVSc DVSc, MACVSc, DACZM 1. Australian Wildlife Heath Centre, Healesville Sanctuary, Zoos Victoria, Parkville, Victoria, 3052, Australia 2. Department of Veterinary Science, University of Melbourne, Parkville, Victoria, 3052, Australia ABSTRACT: Thirty-nine reptiles representing 11 squamate species were used to examine the effects of intravenous alfaxalone. All animals examined were captive-born, healthy, and had no history of chronic illness. Alfaxalone at a dose of 9 mg/kg was injected into the ventral coccygeal vein of each animal, and heart rate, respiratory rate, cloacal temperature, time from loss to regaining righting reflex, spontaneous movement, and response to noxious stimuli were recorded. Intravenous alfaxalone at a dose of 9 mg/kg was an effective sedative in most species examined with no obvious complications observed. Loss of righting reflex was not achieved in four (57.1%) blotched bluetongue lizards (Tiliqua nigrolutea), two (33.3%) coastal carpet pythons (Morelia spilota mcdowelli), and one (50%) red-bellied black snake (Pseudechis porphyriacus). Further research is required for alfaxalone use in these species. KEY WORDS: alfaxalone, anesthesia, induction, intravenous, squamate, ventral coccygeal vein.
INTRODUCTION Captive reptiles frequently require chemical restraint to facilitate clinical examination and surgery; however, their unique anatomy and physiology means that anesthetic management can be difficult. A range of injectable and inhalant agents are used for the induction and maintenance of anesthesia in reptiles, but many of these have undesirable effects such as prolonged induction or recovery times (or both) and respiratory depression (Calderwood and Jacobson, 1979; Bennett, 1998; Bennett et al., 1998; Read, 2004; Mosley, 2005; Schumacher and Yelen, 2006; Ziolo and Bertelsen, 2009). Alfaxalone (3-α-hydroxy-5-α-pregnane-11,20-dione) is a neuroactive steroid molecule with the properties of a general anesthetic (Child et al., 1971). Alfaxalone’s mechanism of action is via modulation of neuronal cell membrane chloride ion transport that is induced by binding of alfaxalone to γ-aminobutyric acid (GABAA) cell surface receptors. These receptors are a common site of action for many anesthetic agents (Harrison and Simmonds, 1984). Alfaxalone was first released in 1971 (Child et al., 1971) and has a high safety margin with a therapeutic index threeto-four–fold greater than that of thiopentone or propofol (Glen, 1980; Hogskilde et al., 1987). Initially, alfaxalone was combined with alphadolone and a polyoxyethylated castor-oil–based surfactant, Cremophor EL (Saffan®, Schering Plough, Hertfordshire, U.K.) (Zaki et al., 2009), but intravenous injection with this solution resulted in hypersensitivity reactions in susceptible individuals, mediated by the release of histamine in response to the presence of the Cremophor EL (Denton et al., 1980; Moneret-Vautrin et al., 1983). Saffan was subsequently excluded from use in many species, including humans and Volume 21, No. 2-3, 2011
dogs, but was continued in cats in Europe and Australia (Zaki et al., 2009). However, administration of Saffan to cats was also associated with a number of potential sideeffects including hyperemia and edema of the pinnae and paws, urticaria and skin erythema, laryngeal edema, hypotension, and occasionally death (Zaki et al., 2009). Due to these deleterious side-effects, Saffan was discontinued in Australia. In 1999, a new aqueous formulation of alfaxalone (without alphadolone) with 2-hydroxypropylbeta-cyclodextrin was released (Alfaxan-CD®, Jurox Pty. Ltd., Rutherford, NSW, Australia) (Zaki et al., 2009). Alfaxan-CD has been safely administered to dogs and cats at five times the prescribed dose (Ferre et al., 2006; Muir et al., 2008; Whittem, 2008). Following intravenous injection, it has a rapid onset of action, rapid redistribution, and a short terminal half-life (approximately 30 min in the dog) (Ferre et al., 2006). There is no perivascular irritation and only minimal cardiovascular respiratory side effects when an induction dose is administered slowly (Muir et al., 2008; Muir et al., 2009). The effects of alfaxalone in a range of reptile species have been reported and include rapid induction with good muscle relaxation when given intravenously but prolonged induction when administered intramuscularly (Calderwood and Jacobson, 1979; Lawrence and Jackson, 1983; Hackenbroich et al., 1998). Anecdotally, the use of alfaxalone in Australian reptiles has resulted in favorable results due to its rapid onset of action and short recovery times. Nevertheless, there are few controlled studies examining its use in this taxon. Therefore, the objective of this investigation was to evaluate alfaxalone as an intravenous anesthetic induction agent in Australian squamate reptiles and to describe some of its physiological effects. Journal of Herpetological Medicine and Surgery
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MATERIALS AND METHODS Animals—Thirty-nine animals representing 11 species from the Healesville Sanctuary reptile collection were used in this pilot study. All animals used in this study were captive-born, and only animals deemed to be healthy based on a history of no chronic disease or current illness were included. Animals were not sedated for any other reason than this study and all were considered to be in good body condition. Species anesthetized were: three eastern bluetongue lizards (Tiliqua scincoides), seven blotched bluetongue lizards (Tiliqua nigrolutea), two coastal bearded dragons (Pogona barbata), six inland bearded dragons (Pogona vitticeps), six Gippsland water dragons (Physignathus lesueurii howittii), two redbellied black snakes (Pseudechis porphyriacus), three lowland copperhead snakes (Austrelaps superbus), three eastern tiger snakes (Notechis scutatus), six coastal carpet pythons (Morelia spilota mcdowelli), and one black-headed python (Aspidites melanocephalus). For the duration of the study, the reptiles were housed under species-specific conditions in the reptile house and were provided with a thermal gradient and access to unfiltered ultraviolet radiation. Animals were fed species-specific diets but were never handled or used in experiments on days following feeding. This experiment was approved by the Zoos Victoria Animal Ethics Committee. Study design and procedure—On the day of experimentation, reptiles were transferred from the reptile house to the Australian Wildlife Heath Centre at Healesville Sanctuary and immediately placed into an intensive care unit set at 32°C (89.6°F). Reptiles remained in the heated unit for a minimum of 1 h prior to induction of anesthesia. After 1 h, each individual was weighed and its activity level and body condition assessed. The reptile was then manually restrained and its pre-anesthetic heart and respiratory rates were recorded. Alfaxalone 9 mg/kg (Alfaxan-CD RTU 10 mg/ml, Jurox Pty. Ltd.) was then injected intravenously into the ventral coccygeal vein over a period of approximately 10 sec. A small amount of blood was drawn into the syringe before and at the end of injection to verify venous administration of the agent. Following injection, all animals were maintained on a warm air blanket kept at 38°C (100°F) for the duration of the study. Reactions were recorded on a standard anesthetic chart. The time to loss of righting reflex was recorded. Once animals had lost the righting reflex, they were intubated and maintained on room air. Heart rate (using Doppler unit [Parks Medical Electronics, Inc., Aloha, OR]), cloacal temperature (using thermometer probe [Welch Allyn, Inc., Skaneateles Falls, NY]), and respiratory rate were measured every 5 min. Depth of anesthesia was assessed at 5 min intervals using palpebral reflex (lizards), tongue withdrawal reflex (snakes), righting reflex, and response to noxious stimuli. In lizards, response to noxious stimulation was assessed via interdigital pinching and in snakes it was assessed via vent and tail pinch. Animals were judged to have recovered once spontaneous movement and righting reflex had returned. Statistical methods—The distribution of the data was evaluated using the Shapiro-Wilk test. Because the data were normally distributed, a repeated measures general linear model was used to evaluate within-animal differences over time for heart rate, respiratory rate, and temperature. 64
Journal of Herpetological Medicine and Surgery
Between-subject differences by species, animal group (snake, lizard), and sex were also evaluated. A power analysis was not conducted as animal numbers used in this experiment were determined by availability in the reptile collection. SPSS 18.0 (SPSS Inc., Chicago, IL) was used to analyze the data. A P-value of
