Evaluating the efficacy of alfaxalone in corn snakes (Pantherophis guttatus)

Impact of procedural handling on the physiological effects of alfaxalone anaesthesia in the ball python (Python regius)

To describe the cardiovascular changes following intramuscular (handled) and intravascular (undisturbed, via intraarterial catheter) alfaxalone administration, we studied 20 healthy ball pythons (Python regius) in a randomised, prospective study. The pythons were instrumented with occlusive arterial catheters to facilitate undisturbed, continuous monitoring of heart rate and blood pressure. Six pythons were administered intramuscular (IM) saline, followed by 20 mg/kg IM alfaxalone, and were manually restrained for both injections. Six pythons received intraarterial (IA) saline, followed by 10 mg/kg IA alfaxalone, and remained undisturbed for both injections. Arterial blood samples were taken at 0, 12 and 60 min post-injection, and heart rate and blood pressure were recorded for 60 min. The remaining eight snakes received 20 mg/kg IM or 10 mg/kg IA alfaxalone (n = 4 per treatment) and were not handled for intubation 10 min post-injection, to examine the effects of handling during anaesthesia. IM administration of 20 mg/kg alfaxalone or an equivalent volume of saline elicited a profound tachycardia and hypertension, which recovered to resting values after 20 min. However, when 10 mg/kg alfaxalone or saline were injected IA, mild hypotension and a lower magnitude tachycardia occurred. Arterial PCO2 and PO2, pH and lactate concentrations did not change following IA alfaxalone, but an acidosis was observed during IM alfaxalone anaesthesia. There were no significant changes in plasma catecholamines and corticosterone among treatments. Handling for injection and during anaesthesia associated with intubation significantly affects cardiovascular parameters, whereas alfaxalone per se only elicits minor changes in cardiovascular physiology.

Sedation and Anesthesia in Exotic Animal Critical Care

Sedation and anesthesia of exotic animals in inherently challenging, but often facilitates the best care for patients. Critical illness or injury adds on another layer of complexity to their management for obtaining diagnostics and providing treatments. This article serves to review some of the more recent literature of sedation and anesthesia within exotics practice, bringing to light some nuances and considerations for when those patients are critically ill or injured.

Pharmacokinetics and pharmacodynamics of intramuscular alfaxalone in central bearded dragons (Pogona vitticeps): Effect of injection site

OBJECTIVE

To evaluate the pharmacodynamic effects and pharmacokinetics of a single intramuscular (IM) injection of alfaxalone in central bearded dragons (Pogona vitticeps) when injected at a cranial versus a caudal site.

STUDY DESIGN

Prospective, masked, randomized crossover study.

ANIMALS

A total of 13 healthy bearded dragons weighing 0.48 ± 0.1 kg.

METHODS

Alfaxalone (10 mg kg^-1) was administered IM to 13 bearded dragons in the triceps muscle (cranial treatment) or the quadriceps muscle (caudal treatment) separated by 4 weeks. Pharmacodynamic variables included movement score, muscle tone score and righting reflex. Blood was obtained from the caudal tail vein using a sparse sampling methodology. Plasma alfaxalone concentrations were determined using liquid chromatography-mass spectrometry, and pharmacokinetic analysis was performed using nonlinear mixed-effects modeling. Differences in variables between injection sites were analyzed using a nonparametric Wilcoxon signed-rank test for paired data with significance set at p ≤ 0.05.

RESULTS

Time to loss of righting reflex score was not different, median (interquartile range), between cranial and caudal treatments [8 (5-11) and 8 (4-12) minutes, respectively, p = 0.72]. Time to recovery of righting reflex was also not different between cranial and caudal treatments [80 (44-112) and 64 (56-104) minutes, respectively, p = 0.75]. Plasma alfaxalone concentrations were not significantly different between treatments. The population estimate (95% confidence intervals) for volume of distribution per fraction absorbed was 1.0 (0.79-1.20) L kg^-1, clearance per fraction absorbed was 9.6 (7.6-11.6) mL minute^-1 kg^-1, absorption rate constant was 2.3 (1.9-2.8) minute^-1 and elimination half-life was 71.9 (52.7-91.1) minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Regardless of the injection site, IM alfaxalone (10 mg kg^-1) produced reliable chemical restraint in central bearded dragons, appropriate for nonpainful diagnostic procedures or anesthetic premedication.

OPTIMIZING THE PHARMACODYNAMICS AND EVALUATING CARDIOGENIC EFFECTS OF THE INJECTABLE ANESTHETIC ALFAXALONE IN PRAIRIE RATTLESNAKES (CROTALUS VIRIDIS)

North American vipers are commonly housed in zoological institutions or studied as free-ranging populations. Because of their venomous predatory and defensive mechanism, sedation or anesthesia is frequently employed to facilitate safe handling and medical procedures, especially of the head. A new formulation of alfaxalone with proprietary preservatives was recently approved and indexed for 28-d use post-vial puncture. Pharmacodynamic effects of alfaxalone in its prior formulation have been researched in nonvenomous species, but the optimal dose and route of administration in vipers have not been reported. In part one, 10 prairie rattlesnakes (Crotalus viridis) participated in a complete four-route crossover study evaluating 20 mg/kg alfaxalone administered intracoelomically (ICo), SC cranial to the heart, IM cranial to the heart, and IV in the ventral coccygeal vein. HR significantly decreased from baseline during IV (P= 0.024), IM (P= 0.024), and SC (P= 0.028) administration. Respiratory rate significantly decreased following alfaxalone delivered IV (P = 0.027). Time to first effects was significantly faster in IV compared with IM (P= 0.01), SC (P= 0.001), and ICo (P= 0.036). All IV and IM administrations resulted in deep sedation, but 70% of the IV and 10% of the IM sedation events resulted in apnea and required intermittent positive ventilation via endotracheal tube. Fifty percent of the ICo sedation events and 10% of the SC sedation events did not result in sedation. One successful SC sedation event resulted in apnea. In part two, echocardiograms were performed in the same rattlesnakes at baseline and at maximum effect of sedation with 20 mg/kg alfaxalone administered IM. Cardiac contractility and output were unaffected. Administration of alfaxalone at 20 mg/kg IM cranial to the heart should facilitate safe handling and minimally invasive procedures in prairie rattlesnakes and related species.

Snake Sedation and Anesthesia

Snakes can be more challenging to anesthetize compared with other animals because of anatomic and physiologic differences, a wide range of patient sizes, and variable responses to anesthetic agents. Snakes have preferred optimal temperature zones, which, along with physiologic characteristics, such as the ability to shunt blood toward or away from the lungs, can have an impact on anesthesia. Injectable agents, including benzodiazepines, α₂-agonists, opioids, propofol, and alfaxalone, as well as inhalant anesthetics can be used to anesthetize snakes. Pain management must be incorporated to the anesthetic plan when performing procedures that are expected to produce nociception.