Research PaperEvaluating the efficacy of alfaxalone in corn snakes (Pantherophis guttatus)
Introduction
Corn snakes (Pantherophis guttatus) are one of the most popular pet snakes in the United States, and remain one of the most commonly bred species of snakes in captivity (https://nationalzoo.si.edu/animals/corn-snake). Corn snakes are routinely presented to veterinarians for examinations, diagnostic testing and surgery. Frequently, injectable anesthesia or sedation is used to perform minor procedures, assist in intubation prior to inhalation anesthesia or aid in physical examination. The only anesthesia reports for corn snakes are limited to case reports (Barten et al. 1994; Burkert et al. 2002; Sykes et al. 2006; d’Ovidio et al. 2011), a cross-sectional study using midazolam (Arnett-Chinn et al. 2016), or an experimental trial with butorphanol and morphine (Sladky et al. 2008). In the work of Arnett-Chinn et al. (2016), midazolam was effective in a variety of snake species for noninvasive and minimally invasive procedures, whereas Sladky et al. (2008) showed that a high dose (20 mg kg–1) of butorphanol (but not morphine) produced antinociceptive effects in corn snakes. However, this dose of butorphanol has been associated with fatalities and should be used with caution (Sladky & Mans 2012). To ensure best practices for corn snakes, it is important to identify anesthetics that can be used to safely manage these animals for a variety of procedures.
Alfaxalone (3α-hydroxy-5α-pregnane-11,20-dione) is a popular anesthetic in veterinary practice. It is a neuroactive steroid derived from progesterone and acts on neuronal cell membrane chloride ion transport through its interaction with cell surface gamma-aminobutyric acid A (GABAA) receptors. This causes hyperpolarization of postsynaptic nerves, resulting in sedation or anesthesia (Jones 2012; Yaw et al. 2018). Alfaxalone can be administered intramuscularly (IM) or subcutaneously (SC) without causing tissue irritation, and intravenously (IV). Alfaxalone is registered for use in cats and dogs; however, it has gained popularity in reptile medicine, with reported effectiveness in numerous species, including leopard geckos (Eublepharis macularius) (Morici et al. 2018), green iguanas (Iguana iguana) (Bertelsen & Sauer 2011; Knotek et al. 2013), bearded dragons (Pogona vitticeps) (Knotek 2017; Perrin & Bertelsen 2017), Rankin’s dragons (Pogona henrylawsoni) (Knotek 2017), Chinese water dragons (Physignathus cocincinus) (Knotek 2017), red-eared slider turtles (Trachemys scripta elegans) (Kischinovsky et al. 2013; Shepard et al. 2013; Knotek 2014), loggerhead sea turtles (Caretta caretta) (Phillips et al. 2017), Hermann’s tortoises (Testudo hermanni) (Knotek 2014), spur-thigh tortoises (Testudo graeca) (Knotek 2014), marginated tortoises (Testudo marginata) (Knotek 2014) and Horsfield’s tortoises (Agrionemys horsfieldii) (Hansen & Bertelsen 2013; Knotek 2014).
Research on the effects of alfaxalone in snakes has been limited to a few species. In common garter snakes (Thamnophis sirtalis) after intracoelomic injections of alfaxalone, the righting reflex was lost faster with 30 mg kg–1 than with 20 mg kg–1 (Strahl-Heldreth et al. 2019). A study of several species of Australian snakes, including red-bellied black snakes (Pseudechis porphyriacus), lowland copperhead snakes (Austrelaps superbus), eastern tiger snakes (Notechis scutatus), coastal carpet pythons (Morelia spilota mcdowelli) and black-headed pythons (Aspidites melanocephalus), reported immediate onset of sedation after administration of alfaxalone (9 mg kg–1) IV in the ventral caudal vein (Scheelings et al. 2011). In ball pythons, anesthetic effects were observed with alfaxalone (10, 20 and 30 mg kg–1) when administered IM in the caudal half of the body (James et al. 2018). In that study, anesthetic duration was longer after alfaxalone (20 mg kg–1) was administered in the cranial half of the body. In the same study, tracheal intubation was only possible with doses of 20 and 30 mg kg–1 administered IM cranially and caudally, respectively. Another study of ball pythons recorded significantly longer and deeper sedation achieved with SC administration of alfaxalone (5 mg kg–1) cranially compared with caudally (Yaw et al. 2018). Differences related to injection site were attributed to the renal portal circulation and faster hepatic metabolism. Many clinicians avoid administering medication in the pelvic limb, tail or caudal half of reptiles assuming that renal or hepatic excretion will be expedited because of this circulatory adaption. At this time, understanding of this system is limited, but it appears to be species and drug specific.
The purpose of this study was to evaluate the anesthetic effects of alfaxalone in corn snakes. It was hypothesized that 1) duration of anesthesia would be significantly increased with increasing doses of alfaxalone (5, 10 and 15 mg kg–1) administered SC in the cranial third of the body; 2) that order of administration will not impact the results; and 3) administration of alfaxalone in the caudal third of the body would result in a significantly shorter duration of anesthesia compared with administration in the cranial third of the body.
Section snippets
Material and methods
A prospective, randomized crossover study was performed in accordance with the regulations of the Louisiana State University Institutional Animal Care and Use Committee (protocol 18-136). A sample size of eight snakes was based on the following a priori assumptions: an alpha of 0.05, power of 0.8, an expected difference in mean anesthesia duration between 5 and 15 mg kg–1 alfaxalone of 10 minutes, and a standard deviation of 6 minutes (MedCalc Statistical Software Version 17.5.5; MedCalc
Results
All of the snakes were determined to be healthy based on physical examination. The median (IQR) (range) of body weight, snout to vent length and tail length of the snakes were 88.1 (67.3–150.6) (56.0–239.8) g, 62.6 (59.1–75.3) (56.0–86.2) cm and 12.6 (11.3–14.8) (11.0–15.7) cm, respectively.
Discussion
Alfaxalone administered SC at 15 mg kg–1 resulted in consistent anesthesia in corn snakes. Although some level of anesthesia was achieved with all doses tested (5, 10 and 15 mg kg–1), a more consistent loss of reflexes was obtained with 15 mg kg–1, making this dose recommended for brief procedures and intubation. However, the presence of a tail pinch response in some of the snakes suggests that additional analgesics are necessary for procedures that elicit a deep pain response.
In reptiles, IM
Conclusions
Anesthetic effects of alfaxalone (5, 10 and 15 mg kg–1) and the effects of the highest dose administered in the cranial and caudal parts of the body were recorded in corn snakes. Alfaxalone produced dose-dependent anesthesia in corn snakes that clinicians may find beneficial for brief, nonpainful procedures. Duration of anesthesia was not influenced by order of dosing or injection site, indicating that the snakes may not develop a tolerance for alfaxalone and that this anesthetic is not
Acknowledgements
The authors thank Fluker Farms (Port Allen, LA, USA) for providing financial support for this project.
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