Pharmacodynamics of alfaxalone after single‐dose intramuscular administration in red‐eared sliders (Trachemys scripta elegans): a comparison of two different doses at two different ambient temperatures

Evaluating the Physiologic Effects of Alfaxalone, Dexmedetomidine, and Midazolam Combinations in Common Blue-Tongued Skinks (Tiliqua scincoides)

Common blue-tongued skinks (Tiliqua scincoides) are popular pet reptiles; however, there has been limited research to investigate sedatives for this species. The purpose of this study was to measure the physiologic effects of four combinations of alfaxalone, dexmedetomidine, and midazolam for minor procedures such as intubation and blood collection. Eleven common blue-tongued skinks (Tiliqua scincoides) were used for this prospective, randomized cross-over study. The subcutaneous combinations were used as follows: 20 mg/kg alfaxalone (A); 10 mg/kg alfaxalone and 1 mg/kg midazolam (AM); 0.1 mg/kg dexmedetomidine and 1 mg/kg midazolam (DM); and 5 mg/kg alfaxalone, 0.05 mg/kg dexmedetomidine, and 0.5 mg/kg midazolam (ADM). Heart rate, respiratory rate, palpebral reflex, righting reflex, escape reflex, toe pinch withdrawal reflex, tongue flicking, and the possibility of intubation were recorded at baseline and every 5 min for 60 min. Venous blood gases were measured at baseline, full sedation, and recovery. Heart and respiratory rates decreased significantly in all groups, but the reductions were most prominent in DM and ADM. Analgesic effects, as measured by the toe pinch withdrawal reflex, were only observed in DM and ADM. Intubation was possible in all four protocols; however, it was not possible in two DM skinks. Based on these trials, ADM and AM are recommended for minor procedures in blue-tongue skinks.

Comparison of Two Intravenous Propofol Doses after Jugular Administration for Short Non-Surgical Procedures in Red-Eared Sliders (Trachemys scripta elegans)

This study compares the effects of two different doses of propofol administered intravenously (IV), in the jugular vein, to red-eared sliders (Trachemys scripta elegans). In this crossover study, 5 or 10 mg/kg propofol was administered to six Trachemys scripta elegans after cannulation of the jugular vein. Each turtle received each dose, G1 (5 mg/kg IV) and G2 (10 mg/kg IV), after a 7-day washout period. The parameters evaluated were heart rate, palpebral reflex, cloacal reflex, muscle relaxation, ease of handling, sensitivity to anterior and posterior pinch stimuli, and possibility of intubation. Additionally, respiratory rate was measured when possible, and the times from propofol administration to full recovery and from intubation to extubation were recorded. None of the turtles in G1 could be intubated, and this dose provided little relaxation and ease of handling, with a duration of effect until full recovery of 12.16 ± 8.32 (SD) min for this group. In G2, five out of the six turtles could be intubated, and the duration of effect was 32.33 ± 5.85 (SD) min. Heart rates were influenced by manipulation for catheter placement. There were statistically significant differences (p value ≤ 0.05) between the two groups in muscle relaxation degree, handling, cloacal reflex, and possibility of intubation. The 5 mg/kg propofol dose was not sufficient to induce anesthesia, even when administered in the jugular vein, in red-eared sliders. A dose of 10 mg/kg IV or higher should be used.

Alfaxalone is an effective anesthetic for the electrophysiological study of anoxia-tolerance mechanisms in western painted turtle pyramidal neurons

Anoxia in the mammalian brain leads to hyper-excitability and cell death; however, this cascade of events does not occur in the anoxia-tolerant brain of the western painted turtle, Chrysemys picta belli. The painted turtle has become an important anoxia-tolerant model to study brain, heart, and liver function in the absence of oxygen, but being anoxia-tolerant likely means that decapitation alone is not a suitable method of euthanasia. Many anesthetics have long-term effects on ion channels and are not appropriate for same day experimentation. Using whole-cell electrophysiological techniques, we examine the effects of the anesthetic, Alfaxalone, on pyramidal cell action potential amplitude, threshold, rise and decay time, width, frequency, whole cell conductance, and evoked GABAA receptors currents to determine if any of these characteristics are altered with the use of Alfaxalone for animal sedation. We find that Alfaxalone has no long-term impact on action potential parameters or whole-cell conductance. When acutely applied to naïve tissue, Alfaxalone did lengthen GABAA receptor current decay rates by 1.5-fold. Following whole-animal sedation with Alfaxalone, evoked whole cell GABAA receptor current decay rates displayed an increasing trend with 1 and 2 hours after brain sheet preparation, but showed no significant change after a 3-hour washout period. Therefore, we conclude that Alfaxalone is a suitable anesthetic for same day use in electrophysiological studies in western painted turtle brain tissue.

COMPARISON OF SUBCUTANEOUS ALFAXALONE AND SUBCUTANEOUS ALFAXALONE-DEXMEDETOMIDINE FOR SEDATION IN THE HOUSTON TOAD (ANAXYRUS HOUSTONENSIS)

The Houston toad (Anaxyrus houstonensis), a primarily terrestrial amphibian of south-central Texas, has been listed as federally endangered since 1970. Sedation is an important tool for obtaining diagnostics and providing treatment in this species. This prospective, randomized, and blinded study compared the sedative effects of SC alfaxalone (Protocol A) at approximately 12 mg/kg (median [range] = 12.70 [12.09-13.95] mg/kg] to SC alfaxalone-dexmedetomidine (Protocol AD) at approximately 12 mg/kg (median [range] = 12.68 [12.16-13.56] mg/kg) and 0.1 mg/kg (median [range] = 0.1 [0.07-0.13] mg/kg), respectively, in adult Houston toads (n = 26). Toads from Protocol AD received atipamezole SC at approximately 1 mg/kg (median [range] = 0.96 [0.75-1.25] mg/kg) 45 min postinduction, whereas toads from Protocol A received the equivalent volume of SC sterile saline at the same time point. Heart rate, gular rate, and times to first effect, loss of righting reflex, ability to position for radiographs, loss of nociception, return of righting reflex, and full recovery were recorded. A significantly greater number of toads lost righting reflex, positioned for radiographs, and lost nociception with Protocol AD compared with Protocol A. Additionally, time to return of righting reflex and time to full recovery were significantly longer with Protocol AD than with Protocol A. The protocols did not differ significantly in time to first effect, time to radiographic positioning, or time to loss of nociception. Histologic examination of four toads euthanized during the study revealed acute injection site reactions from all administered drugs, including saline. No clinical adverse reactions were observed. This study demonstrates that the combination of SC alfaxalone and dexmedetomidine results in deeper sedation than SC alfaxalone alone, but also correlates with longer recovery times despite antagonist administration.

Evaluating the Anesthetic and Physiologic Effects of Intramuscular and Intravenous Alfaxalone in Eastern Mud Turtles (Kinosternon subrubrum)

Current sedation protocols for chelonians can pose a challenge to clinicians because of prolonged induction and recovery times, difficulties in gaining venous access, and natural species variation. This study evaluated the sedative and physiologic effects of intramuscular (IM) and intravenous (IV) alfaxalone in six wild-caught adult eastern mud turtles (Kinosternon subrubrum). The turtles received alfaxalone 10 mg/kg IM and IV in a randomized cross-over design. A 10-day washout period occurred between trials. Baseline parameters (heart rate, respiratory rate, temperature, and reflexes) were assessed prior to injection and every 5 min post-injection until recovery. Three venous blood gas samples were also collected and analyzed over the course of each trial (baseline, induction, and recovery). Intravenous alfaxalone resulted in a significantly faster induction (p = 0.016; median: 1.5 min, 25-75%: 1-7.5, minimum-maximum: 1-21) and a shorter total sedation time (p = 0.041; median: 52 min, 25-75%: 34.5-62.5, minimum-maximum: 33-87) when compared with IM alfaxalone (induction, median: 20 min, 25-75%: 15-22.5, minimum-maximum: 15-25; total, median: 70 min, 25-75%: 65-82.5, minimum-maximum: 65-90). Blood gas and physiologic parameters were not significantly different between groups; however, the pH (p = 0.009) and glucose (p = 0.0001) significantly increased, and partial pressure of carbon dioxide (p = 0.024) significantly decreased over time. This study demonstrated that alfaxalone 10 mg/kg IV or IM can be used to provide safe and effective sedation in eastern mud turtles.

Comparison of intramuscular alfaxalone with medetomidine-ketamine for inducing anaesthesia in Trachemys scripta spp. undergoing sterilization

OBJECTIVE

To compare the effect of two anaesthetic protocols on heart rate (HR), time to muscle relaxation and tracheal intubation and time to surgical plane of anaesthesia, in Trachemys scripta spp. undergoing oophorectomy.

STUDY DESIGN

Prospective randomized clinical study.

ANIMALS

A total of 43 healthy female turtles.

METHODS

Morphine (1.5 mg kg-1) was injected subcutaneously 2 hours before anaesthesia induction. The turtles were randomly administered either medetomidine (0.2 mg kg-1) and ketamine (10 mg kg-1) (group MK; n = 23) or alfaxalone (20 mg kg-1) (group A; n = 20) intramuscularly followed by bupivacaine (2 mg kg-1) administered subcutaneously along the incision site. Anaesthesia was maintained with isoflurane delivered in oxygen (100%). HR and the anaesthetic depth score (ADS) were recorded every 5 minutes from induction to recovery. A Friedman test followed by Wilcoxon tests with Bonferroni adjustment were used to compare these non-parametric data (HR and ADS) between groups and over time. Time to muscle relaxation of neck and limbs (TMR), tracheal tube insertion (TTTI) and stage of surgical anaesthesia (TADS≤3) were recorded and compared between groups using a Welch's t test after logarithmic transformation.

RESULTS

Median values of TMR, TTTI and TADS≤3 were 4, 9.5 and 25 minutes in group A, respectively, and 14, 20 and 35 minutes in group MK (TMR, TTTIp ≤ 0.0001; TADS≤3p = 0.001). Plane of anaesthesia was significantly deeper in group A than in group MK for the first 20 minutes (p < 0.01). HR at 10 and 15 minutes post injection was significantly lower in group MK (28 beats minute-1) than in group A (36 and 34 beats minute-1) (p < 0.02).

CONCLUSIONS AND CLINICAL RELEVANCE

After intramuscular injection in Trachemys scripta spp., tracheal intubation, muscle relaxation and a surgical plane of anaesthesia developed faster with alfaxalone than medetomidine-ketamine.

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.

Chelonian Sedation and Anesthesia

Anesthetic management of chelonians represents a unique challenge; the order Chelonia includes numerous species that display diverse anatomic features, habitats, body sizes, temperaments, and metabolic rates. Owing to their peculiar characteristics, safe and effective sedation and anesthesia may be more complicated than in other animals. For example, gas inductions are not indicated, and intravenous catheterization requires practice. The pharmacology of anesthetic drugs is severely impacted by body/environmental temperature, site of administration, and organ function. This review will summarize the current knowledge in terms of anatomy, physiology, and drug metabolism in chelonians, before discussing practical aspects of anesthesia.

Evaluation of the effects of a dexmedetomidine-midazolam-ketamine combination administered intramuscularly to captive red-footed tortoises (Chelonoidis carbonaria)

OBJECTIVE

To evaluate the effects of a dexmedetomidine-midazolam-ketamine (DMK) combination administered IM to captive red-footed tortoises (Chelonoidis carbonaria).

ANIMALS

12 healthy adult red-footed tortoises.

PROCEDURES

In a prospective experimental study, DMK (0.1, 1.0, and 10 mg/kg, respectively) was administered IM as separate injections into the right antebrachium. Atipamezole (0.5 mg/kg, IM) and flumazenil (0.05 mg/kg, SC) were administered into the left antebrachium 60 minutes later. Times to the first treatment response and maximal treatment effect after DMK administration and time to recovery after reversal agent administration were recorded. Vital signs and reflexes or responses to stimuli were assessed and recorded at predetermined intervals.

RESULTS

DMK treatment produced deep sedation or light anesthesia for ≥ 20 minutes in all tortoises. Induction and recovery were rapid, with no complications noted. Median times to first response, maximum effect, and recovery were 4.5, 35, and 14.5 minutes, respectively. Two tortoises required additional reversal agent administration but recovered < 20 minutes after the repeated injections. Mean heart and respiratory rates decreased significantly over time. All animals lost muscle tone in the neck and limbs from 35 to 55 minutes after DMK injection, but other variables including palpebral reflexes, responses to mild noxious stimuli (eg, toe pinching, tail pinching, and saline ([0.9 NaCl] solution injection), and ability to intubate were inconsistent.

CONCLUSIONS AND CLINICAL RELEVANCE

DMK administration produced deep sedation or light anesthesia with no adverse effects in healthy adult red-footed tortoises. At the doses administered, deep surgical anesthesia was not consistently achieved. Anesthetic depth must be carefully evaluated before performing painful procedures in red-footed tortoises with this DMK protocol.

Pharmacodynamics of propofol and alfaxalone in rattlesnakes (Crotalus durissus)

To characterise the effect of two common induction agents, propofol and alfaxalone, on mean arterial blood pressure (MAP) and heart rate (HR), we equipped 19 adult South American rattlesnakes (Crotalus durissus) with an indwelling arterial catheter approximately 24 h prior to recording of baseline resting values. Then, seven snakes received alfaxalone (15 mg kg^-1) intravascularly (IV) through the catheter, while groups two and three (both n = 6) received propofol (15 mg kg^-1 IV). The first two groups were not handled, while the group 3 was manually restrained for 2 min for a mock injection of 0.2 ml saline into the ventral tail vein. Baseline HR was similar in all groups and handling caused a significant tachycardia (p = 0.031) in group three. When given IV to undisturbed animals, both propofol and alfaxalone induced a significant increase in HR (p = 0.0022 and p = 0.0045, respectively) lasting approximately 30 min, but with values only significantly exceeding baseline for the first 5 min for propofol and the first 10 min with alfaxalone. Handling caused a significant increase in MAP (p = 0.0313). Propofol did not affect MAP (p = 0.1064), while alfaxalone caused a marked hypertension (although only significant at 2 min; p = 0.031). Manual restraint significantly increases both HR and MAP, which may lead to a masking of true cardiovascular effects of anaesthetic agents.

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

OBJECTIVE

Alfaxalone is a popular veterinary anesthetic; however, research on this anesthetic in snakes has been limited to ball pythons, garter snakes and several Australian species. The objective was to evaluate the anesthetic effects of alfaxalone in corn snakes (Pantherophis guttatus), a popular pet snake.

STUDY DESIGN

Prospective, randomized crossover study.

ANIMALS

A total of eight corn snakes.

METHODS

In phase I, snakes were subcutaneously administered three doses of alfaxalone (5, 10 and 15 mg kg^-1) in the cranial third of the body to determine the most effective dose. In phase II, a dose of 15 mg kg^-1 was administered in the cranial and caudal thirds of the snakes to determine if injection site affected anesthesia duration. Heart rate (HR), respiratory rate (f_R), righting reflex, escape response, tail pinch, needle prick and tongue flick were monitored at baseline and 5 minute intervals until the snakes fully recovered.

RESULTS

Duration of anesthesia differed significantly, with higher doses lasting longer than lower doses: 5 mg kg^-1 [23.8 ± 4.4 (15-30) minutes]; 10 mg kg^-1 [40.6 ± 9.4 (25-55) minutes]; and 15 mg kg^-1 [56.9 ± 8.4 (50-70) minutes], mean ± standard deviation (range). The tail pinch reflex was not completely lost in phase 1. There was a significant change in f_R over time, but this was not related to dose. HR was not different by time or dose. Duration of anesthesia was not different after administration of alfaxalone (15 mg kg^-1) in the cranial third versus the caudal third of the body; however, there was a significant decrease in HR and f_R at this dose, regardless of injection site.

CONCLUSIONS AND CLINICAL RELEVANCE

Based on these results, alfaxalone (15 mg kg^-1) provides adequate anesthesia for brief procedures or intubation; however, additional analgesia is required for painful procedures.

SEDATIVE AND CARDIORESPIRATORY EFFECTS OF INTRAMUSCULAR ALFAXALONE AND BUTORPHANOL AT TWO DOSAGES IN FERRETS (MUSTELA PUTORIUS FURO)

Veterinary care of ferrets often requires chemical restraint. This study hypothesized that IM alfaxalone and butorphanol would result in clinically useful sedation without clinically relevant cardiorespiratory effects. Twelve healthy 15-mo-old ferrets of equal sexes weighing 0.75 to 1.66 kg were enrolled. Using a prospective, blinded design, ferrets randomly received either IM alfaxalone 2.5 mg/kg and butorphanol 0.2 mg/kg (low dose [LD]) or IM alfaxalone 5 mg/kg and butorphanol 0.2 mg/kg (high dose [HD]) (n = 6/group). Sedation times and induction and recovery scores were recorded by a blinded observer. Anesthetic monitor placement was attempted in all recumbent ferrets, and physiologic parameters and reflexes were recorded every 5 min until return of spontaneous movement. Data were assessed for normality using a Shapiro-Wilk normality test and analyzed by two-sample t test or Mann-Whitney U test; one ferret in HD was excluded. Ferrets in LD and HD exhibited moderate and marked sedation, with one of six and four of five ferrets tolerating monitor placement, respectively. Mean ± SD time to first effects, recumbency, and recovery in LD and HD was 2.30 ± 1.13 and 2.054 ± 1.12 (P = 0.7240), 2.87 ± 1.25 and 2.72 ± 1.41 (P = 0.8529), and 65.43 ± 32.43 and 52.30 ± 13.19 (P = 0.4212), respectively. Median (range) duration of recumbency in LD and HD was 31.12 (25.58-115.72) and 35.47 (28.27-44.42) min (P = 0.3290), respectively. Among monitored ferrets, transient mild hypotension and hypoxemia were observed. Intramuscular alfaxalone 5 mg/kg with butorphanol 0.2 mg/kg provided clinically useful sedation in ferrets with mild transient cardiorespiratory derangements.

Evaluation of subcutaneous administration of alfaxalone-midazolam and dexmedetomidine-midazolam for sedation of ball pythons (Python regius)

OBJECTIVE

To evaluate SC administration of alfaxalone-midazolam and dexmedetomidine-midazolam for sedation of ball pythons (Python regius).

ANIMALS

12 healthy juvenile ball pythons.

PROCEDURES

In a randomized crossover study, each snake was administered a combination of alfaxalone (5 mg/kg [2.3 mg/lb]) and midazolam (0.5 mg/kg [0.23 mg/lb]) and a combination of dexmedetomidine (0.05 mg/kg [0.023 mg/lb]) and midazolam (0.5 mg/kg), SC, with a washout period of at least 7 days between protocols. Respiratory and heart rates and various reflexes and behaviors were assessed and compared between protocols. Forty-five minutes after protocol administration, sedation was reversed by SC administration of flumazenil (0.05 mg/kg) alone or in combination with atipamezole (0.5 mg/kg; dexmedetomidine-midazolam protocol only). Because of difficulties with visual assessment of respiratory effort after sedative administration, the experiment was repeated for a subset of 3 ball pythons, with plethysmography used to assess respiration.

RESULTS

Both protocols induced a similar level of moderate sedation with no adverse effects aside from transient apnea. Cardiopulmonary depression was more profound, but time to recovery after reversal was significantly shorter, for the dexmedetomidine-midazolam protocol than for the alfaxalone-midazolam protocol. Plethysmographic findings were consistent with visual observations and suggested that snakes compensated for a decrease in respiratory rate by increasing tidal volume amplitude.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that both protocols induced clinically relevant sedation in ball pythons and should be useful for minor procedures such as venipuncture and diagnostic imaging. However, caution should be used when sedating snakes with compromised cardiopulmonary function. (J Am Vet Med Assoc 2020;256:573-579.

The Use of Alfaxalone in Quaker Parrots (Myiopsitta monachus)

Alfaxalone is a neurosteroid anesthetic that acts on gamma-aminobutyric acid alpha-receptors. The objective of this study was to evaluate the clinical safety and efficacy of alfaxalone (Alfaxan CD). Due to observed hyperexcitability in the subject animals when alfaxalone was the only drug used during the initial trials, premedication with midazolam was also evaluated during the final study. Ten adult Quaker parrots (Myiopsitta monachus) were assigned to 3 groups: 1) low-dose alfaxalone 10 mg/kg (LD), 2) high-dose alfaxalone 25 mg/kg (HD), and 3) alfaxalone 10 mg/ kg with midazolam 1 mg/kg premedication (AM), administered intramuscularly. Induction time, sedation quality, duration of action, and vital parameters, including heart rate, respiratory rate, and temperature, were recorded. All protocols achieved adequate sedation; however, muscle tremors and hyperexcitation were variable. The LD group had a significantly longer mean ± SD induction time (13.5 ± 4.5 minutes) as compared to the HD (6.0 ± 1.3 minutes, P = .002) and AM (6.5 ± 2.9 minutes, P = .006) groups, while recovery time was significantly longer in the HD group (86.2 ± 13.4 minutes) than the LD group (44.4 ± 10.8 minutes, P < .001). Midazolam premedication resulted in reduction of both muscle tremors and hyperexcitation associated with alfaxalone administration, but the recovery time was significantly longer (103.5 ± 15.1 minutes, P < .001) than for the LD group. Alfaxalone as a sole agent resulted in muscle tremors and hyperexcitation during induction, which was attenuated by premedication with midazolam. Further investigation is warranted to characterize the effects of alfaxalone and drugs used to premedicate Quaker parrots.

Pharmacokinetics and pharmacodynamics of alfaxalone after a single intramuscular or intravascular injection in mallard ducks (Anas platyrhynchos)

Pharmacokinetics and pharmacodynamics of alfaxalone was performed in mallard ducks (Anas platyrhynchos) after single bolus injections of 10 mg/kg administered intramuscularly (IM; n = 10) or intravenously (IV; n = 10), in a randomized cross-over design with a washout period between doses. Mean (±SD) C_max following IM injection was 1.6 (±0.8) µg/ml with T_max at 15.0 (±10.5) min. Area under the curve (AUC) was 84.66 and 104.58 min*mg/ml following IV and IM administration, respectively. Volume of distribution (V_D ) after IV dose was 3.0 L/kg. The mean plasma clearance after 10 mg/kg IV was 139.5 (±67.9) ml min^-1  kg^-1 . Elimination half-lives (mean [±SD]) were 15.0 and 16.1 (±3.0) min following IV and IM administration, respectively. Mean bioavailability at 10 mg/kg IM was 108.6%. None of the ducks achieved a sufficient anesthetic depth for invasive procedures, such as surgery, to be performed. Heart and respiratory rates measured after administration remained stable, but many ducks were hyperexcitable during recovery. Based on sedation levels and duration, alfaxalone administered at dosages of 10 mg/kg IV or IM in mallard ducks does not induce clinically acceptable anesthesia.

RANDOMIZED CONTROLLED TRIAL COMPARING THE EFFECTS OF ALFAXALONE AND KETAMINE HYDROCHLORIDE IN THE HAITIAN GIANT GALLIWASP ( CELESTUS WARRENI)

  The immobilization properties and cardiopulmonary effects following intramuscular administration of one of two chemical immobilization agents were compared in the Haitian giant galliwasp ( Celestus warreni) in a prospective, blinded, randomized controlled trial. Adult, clinically healthy galliwasps ( n = 30) were given a randomly assigned single intramuscular injection of either 15 mg/kg alfaxalone ( n = 15) or 40 mg/kg ketamine hydrochloride ( n = 15). Heart rate, respiratory rate, and depth classification stage were recorded every 5 min; cloacal temperature was recorded every 15 min to ensure maintenance within this species' preferred optimal temperature range (75-85°F, 24-29°C). Physical examination, radiographs, and phlebotomy were performed in all animals. Alfaxalone given intramuscularly resulted in reliable anesthetic induction, maintenance, and recovery (total duration of anesthesia 57.7 ± 23.6 min, recovery 7.9 ± 7.8 min). Ketamine hydrochloride resulted in variable levels of sedation or anesthesia and a longer recovery (total duration of anesthesia 14 ±17.5 min, recovery 47.9 ± 19.3 min). Heart and respiratory rates remained within clinically acceptable ranges in all lizards using both protocols; however, alfaxalone animals had lower heart rates and respiratory rates associated with increased anesthetic depth as compared to ketamine hydrochloride animals (heart rates: alfaxalone 59.6 ± 13.3 beats/min, ketamine hydrochloride 71.9 ± 7.9 beats/min; respiratory rates: alfaxalone 33.4 ± 16.8 breaths/min, ketamine hydrochloride 50.0 ± 16.2 breaths/min). Duration of anesthesia for alfaxalone-treated galliwasps was longer than previously reported in other studies. This study determined that a single injection of alfaxalone at 15 mg/kg administered intramuscularly can be used for consistent induction and maintenance of anesthesia and prompt recovery in the Haitian giant galliwasp, while ketamine hydrochloride even at 40 mg/kg was unreliable and is not recommended as a sole immobilization agent in the Haitian giant galliwasp.

Pharmacokinetics of subcutaneously administered hydromorphone in bearded dragons (Pogona vitticeps) and red-eared slider turtles (Trachemys scripta elegans)

OBJECTIVE

To determine pharmacokinetic dosing strategy in bearded dragons (Pogona vitticeps) and red-eared sliders (Trachemys scripta elegans) based on two subcutaneously (SC) administered doses of hydromorphone (0.5 and 1.0 mg kg^-1).

STUDY DESIGN

Randomized crossover study.

ANIMALS

Six healthy adult bearded dragons, seven healthy adult red-eared slider turtles.

METHODS

Hydromorphone (0.5 and 1.0 mg kg^-1; 2 mg mL^-1) was administered SC dorsolateral to the scapulae in the bearded dragons and between the head and thoracic limb of the red-eared slider turtles. Blood was collected for hydromorphone plasma concentration analysis from the ventral tail vein in bearded dragons and subcarapacial sinus in turtles before (time 0) hydromorphone administration and at 0.5, 1, 6, 12 and 24 hours.

RESULTS

The half-life of hydromorphone administered at 0.5 and 1.0 mg kg^-1 was 2.54 and 3.05 hours in bearded dragons and 2.67 and 2.01 hours in red-eared sliders, respectively. The maximum plasma concentrations for 0.5 and 1.0 mg kg^-1 were 142 and 369 ng mL^-1 in bearded dragons and 1610 and 5142 ng mL^-1 in red-eared sliders, respectively. Peak plasma concentrations were detected at 30 minutes for both species. Hydromorphone administered at both dosages provided plasma concentrations of 13-14 ng mL^-1 for at least 24 hours in bearded dragons and of 5-6 ng mL^-1 for at least 12 hours in red-eared sliders. Clinical sedation was observed for up to 1 hour posthydromorphone (1.0 mg kg^-1) administration for five of six bearded dragons characterized by low body carriage and decreased response to stimuli. No evidence of clinical sedation was observed in red-eared sliders at either dose.

CONCLUSIONS AND CLINICAL RELEVANCE

Recommended dosing strategy for hydromorphone is 0.5 mg kg^-1 administered SC every 24 hours in bearded dragons and every 12-24 hours in red-eared sliders.

A fixed moderate-dose combination of tiletamine+zolazepam outperforms midazolam in induction of short-term immobilization of ball pythons (Python regius)

Laboratory animals are commonly anesthetized to prevent pain and distress and to provide safe handling. Anesthesia procedures are well-developed for common laboratory mammals, but not as well established in reptiles. We assessed the performance of intramuscularly injected tiletamine (dissociative anesthetic) and zolazepam (benzodiazepine sedative) in fixed combination (2 mg/kg and 3 mg/kg) in comparison to 2 mg/kg of midazolam (benzodiazepine sedative) in ball pythons (Python regius). We measured heart and respiratory rates and quantified induction parameters (i.e., time to loss of righting reflex, time to loss of withdrawal reflex) and recovery parameters (i.e., time to regain righting reflex, withdrawal reflex, normal behavior). Mild decreases in heart and respiratory rates (median decrease of <10 beats per minute and <5 breaths per minute) were observed for most time points among all three anesthetic dose groups. No statistically significant difference between the median time to loss of righting reflex was observed among animals of any group (p = 0.783). However, the withdrawal reflex was lost in all snakes receiving 3mg/kg of tiletamine+zolazepam but not in all animals of the other two groups (p = 0.0004). In addition, the time for animals to regain the righting reflex and resume normal behavior was longer in the drug combination dose groups compared to the midazolam group (p = 0.0055). Our results indicate that midazolam is an adequate sedative for ball pythons but does not suffice to achieve reliable immobilization or anesthesia, whereas tiletamine+zolazepam achieves short-term anesthesia in a dose-dependent manner.

Microbial integrity of preservative-free alfaxalone in a multiple-use system for two storage conditions and three handling techniques

OBJECTIVE To evaluate the microbial integrity of preservative-free cyclodextrin-based alfaxalone in a multiple-use system. SAMPLE 22 vials of preservative-free alfaxalone. PROCEDURES 2 storage conditions (room temperature, 22°C; refrigerated temperature, 4°C) and 3 handling techniques (closed system transfer device, nonclosed dispensing pin, and manufacturer-supplied vial stopper) comprised 6 treatment groups (3 replicates/group). An aliquot (0.5 mL) was withdrawn from each vial daily for 14 days. Samples were immediately inoculated into tryptic soy broth and incubated at 36°C for 24 hours; samples were subcultured onto 5% Columbia sheep blood agar and incubated for 48 hours. Isolated colonies were evaluated for identification. RESULTS There was no evidence of microbial contamination of vials stored for 7 days in refrigeration and handled with a protected port (closed system transfer device or nonclosed dispensing pin). CONCLUSIONS AND CLINICAL RELEVANCE The US FDA prohibits the use of alfaxalone beyond 6 hours after the vial stopper is broached (punctured), as mandated for a preservative-free injectable medication. Findings for the study reported here supported the use of alfaxalone for 7 days when refrigerated and handled with a single puncture of the stopper by use of a protected port (closed system transfer device or nonclosed dispensing pin). This would appear to be a practical alternative for an injectable anesthetic. It would minimize drug waste and the subsequent environmental impact for disposal of unused drug and allow standardization of storage and handling protocols for alfaxalone use in veterinary practices across the United States.

Advancements in Evidence-Based Anesthesia of Exotic Animals

Anesthesia and sedation of pet nondomestic species are often necessary for both invasive and noninvasive procedures. Even minimally invasive procedures can be stressful for small prey species that are not domesticated or acclimated to human contact and restraint. Recent advancements in evidence-based practice will continue to improve the field based on scientifically sound best practices and rely less on anecdotal recommendations. This article focuses on new scientific literature that has been published in the past 5 years. For ease of reading, the authors divide the article to highlight advances in anesthetic pharmacology and discoveries in anesthetic physiology and monitoring.

The hairy lizard: heterothermia affects anaesthetic requirements in the Arabian oryx (Oryx leucoryx)

OBJECTIVE

To study the effect of heterothermia on anaesthetic drug requirements in semi-free ranging Arabian oryx and to assess the temperature quotient (Q₁₀) of oxygen consumption.

STUDY DESIGN

Prospective observational study and controlled metabolic experiment.

ANIMALS

Sixty-eight anaesthetic events in 59 Arabian oryx from Mahazat As-Sayd protected area, Saudi Arabia METHODS: Anaesthesia was induced by remote injection of 25 mg ketamine, 10 mg midazolam and 0.5 mg medetomidine with a variable amount of etorphine based on a target dosage of 20 μg kg^-1 and subjective assessment of body mass. Animals not recumbent within 15 minutes or insufficiently anaesthetized were physically restrained and administered supplementary etorphine intravenously depending on the anaesthetic depth. Body temperature (Tb) was measured rectally immediately upon handling of each animal. From six anaesthetized oryx, expiratory gasses for oxygen analysis and metabolic rate calculation were collected at two Tbs; before and after submersion in ice water for approximately 30 minutes.

RESULTS

Forty-two animals (62%) became recumbent with the initial dose, with a mean induction time (± standard deviation) of 9 ± 2 minutes. The remaining animals could be handled but needed 0.3 ± 0.1 mg etorphine intravenously to reach the desired level of anaesthesia. There was a significant positive correlation between Tb and effective etorphine dosage (R² = 0.48, p < 0.0001). Average Tb of the six animals in which metabolic rate was measured decreased from 40.0 ± 0.5°C immediately after induction to 35.5 ± 0.5°C after cooling. This reduction was associated with a reduction in oxygen uptake from 3.11 ± 0.33 to 2.22 ± 0.29 mL O₂ minute^-1 kg^-1, reflected in Q₁₀ of 2.17 ± 0.14.

CONCLUSIONS AND CLINICAL RELEVANCE

Tb significantly affects anaesthetic requirements in Arabian oryx and should be considered when selecting dosages for anaesthetic induction for species showing diurnal heterothermy.