Daily and seasonal features in the hind limb withdrawal latency of tegus (Salvator merianae) and green iguanas (Iguana iguana)

This study evaluated the effects of daytime and season on the limb withdrawal latency time (LWLT) of lizards. Captive-raised, juvenile tegus and green iguanas (n = 6 each) were housed indoors, where a temperature gradient (27-40 °C) and a constant photoperiod (12-h cycle) were provided. Body temperatures and LWLT were measured at 00:00 h, 06:00 h, 12:00 h and 18:00 h over winter, spring, summer and fall. Both lizards had body temperatures lower than 30 °C at 00:00 h/06:00 h and higher than 30 °C at 12:00 h/18:00 h. In spring, tegus had higher body temperatures than in fall at 12:00 h (34.2 ± 1.4 °C versus 30.3 ± 1.9 °C) and in winter at 18:00 h (33.6 ± 1.2 °C versus 30.4 ± 1.0 °C); iguanas presented increased body temperatures at 00:00 h in summer (28.1 °C [28.0-28.2]) compared to winter (25.5 °C [25.3-25.7]). The LWLT of tegus was elevated at 06:00 h compared to 12:00 h and 18:00 h in winter (12.0 ± 3.8 s versus 7.6 ± 1.8 s and 7.0 ± 3.2 s, respectively), spring (12.0 ± 2.7 s versus 7.4 ± 3.1 s and 7.7 ± 1.3 s, respectively) and fall (14.8 ± 2.3 s versus 10.2 ± 1.2 s and 8.9 ± 1.9 s, respectively). Iguanas showed season-related fluctuations in LWLT, with higher values at 18:00 h in winter (15.5 ± 6.1 s) and fall (14.8 ± 2.6 s) than in summer (9.2 ± 1.9 s), as well as higher at 00:00 h (16.6 ± 5.4 s) and 12:00 h (15.4 ± 3.9 s) in spring than in summer (11.0 ± 2.9 s and 9.3 ± 1.3 s, respectively). Body temperature was poorly correlated with LWLT in tegus (rs = - 0.292; p = 0.003) and iguanas (rs = - 0.143; p = 0.162). Researchers should consider circadian and circannual rhythms as potential biases in antinociception-focused lizard studies.

SERUM FENTANYL CONCENTRATIONS AND BEHAVIOR ASSOCIATED WITH TRANSDERMAL FENTANYL APPLICATION ON HEALTHY CORN SNAKES (PANTHEROPHIS GUTTATUS)

Snakes are common household pets and frequently managed in zoos. Geriatric snakes commonly develop osteoarthritis, leading to a declining quality of life that often results in euthanasia. Anecdotally, the application of transdermal fentanyl patches (TFP) appears to contribute to clinical improvement, including increased activity level, in osteoarthritic snakes presumed to be in pain. This study evaluated serum fentanyl concentrations over time and the effects of TFP on the normal behavior of healthy, captive, adult corn snakes (Pantherophis guttatus) using constant video monitoring. Serum fentanyl concentrations were evaluated over 4 wk during 12.5 µg/h TFP application, and the results demonstrated long-lasting (>4 wk) serum concentrations that were consistent with analgesic efficacy in mammalian species during TFP application. At 4 wk of TFP application, mean serum fentanyl concentrations were 11.5 ± 5.5 ng/ml. Snakes were videotaped for 1 wk prior to and 2 wk after 12.5 µg/h TFP application, and behavior was evaluated by an ethogram. Behavioral changes associated with TFP application included decreased mean time spent active, decreased mean number of climbs, and decreased mean number of water visits; feeding behavior was unchanged. Overall, these results suggest that TFP application may provide safe, clinically effective analgesia in healthy corn snakes for at least 4 wk without inducing deleterious side effects, and may therefore be appropriate analgesia for management of osteoarthritic snakes.

Antinociceptive effects of nortriptyline and desipramine hydrochloride in Speke's hinge-back tortoise (Kinixys Spekii)

Some of the most commonly used analgesic drugs in animals are of questionable efficacy or present adverse side effects among the various species of reptiles. Tricyclic antidepressants have been demonstrated to have antinociceptive effects in several animal models of pain and could be a good alternative for use in reptiles. The aim of the study was to investigate the antinociceptive effects of nortriptyline and desipramine hydrochloride in Speke's hinge-back tortoise. A total of 24 animals weighing 600-1000 g were used for nociceptive tests, i.e., formalin, capsaicin, and hot plate tests. Drugs were administered intracoelomically 30 min before starting the tests. The time spent in nocifensive behavior and the associated observable effects during the tests were recorded. Only the highest dose of 40 mg/kg of nortriptyline hydrochloride caused statistically significant decrease in nocifensive behavior in both the formalin and the capsaicin test. Desipramine hydrochloride at doses of 20 and 40 mg/kg caused statistically significant decrease in nocifensive behavior in the formalin test. Also, desipramine hydrochloride at doses of 15, 20, and 60 mg/kg caused statistically significant decrease in nocifensive behavior in the capsaicin test. None of the doses used for both drugs had any statistically significant effect on nocifensive behavior in the hot plate test. The results show that nortriptyline and desipramine hydrochloride have significant antinociceptive effects in the chemical but not thermal inflammatory pain-related behavior in the Speke's hinge-back tortoise. The most common associated side effect following administration of the higher doses of either of the drugs is excessive salivation.

Treatment of Pain in Reptiles

This chapter provides an overview of our current understanding of clinical analgesic use in reptiles. Currently, μ-opioid agonist drugs are the standard of care for analgesia in reptiles. Reptile pain is no longer considered a necessary part of recovery to keep the reptile from becoming active too early. Rather, treating pain allows for the reptile to begin normalizing their behavior. This recognition of pain and analgesia certainly benefits our reptile patients and greatly improves reptile welfare, but it also benefits our students and house officers, who will carry the torch and continue to demand excellence in reptile medicine.

Use of alfaxalone in bearded dragons (Pogona vitticeps): optimizing pharmacodynamics and evaluating cardiogenic effects via echocardiography

OBJECTIVE

Bearded dragons (Pogona vitticeps), a popular zoological companion species, frequently require sedation for procedures. A novel formulation of alfaxalone with preservatives was FDA approved for 28-day use after the vial is breached. Research has been performed in squamate species using alfaxalone without preservatives at various doses and routes of administration, but it is unknown whether preservatives affect quality of sedation or cardiac function.

ANIMALS

10 bearded dragons.

PROCEDURES

This complete crossover study evaluated the pharmacodynamic effects of alfaxalone with preservatives administered to bearded dragons via intracoelomic (ICo; n = 10), SC (10), IM (9), and IV (9) injection at 15 mg/kg.

RESULTS

Deep sedation was achieved in 9 of 10 ICo, 8 of 10 SC, 8 of 9 IM, and 9 of 9 IV administrations. Heart rate significantly decreased from baseline for ICo (P = .008; median heart rate, 46), IM (P = .018; 54), and IV (P = .033; 54) routes, but maintained within clinically acceptable limits. Respiratory rate significantly decreased from baseline for ICo (P = .011; median respiratory rate, 30), SC (P = .024; 12), IM (P = .028; 12), and IV (P = .043; 12) routes. Spontaneous ventilation was retained during all events. Time to first effects was significantly sooner with IV (0 min) administration compared with ICo (P = .02; 5 min) and IM (P = .008; 5 min). Time to loss and recovery of withdrawal, righting reflex, deep pain, and purposeful movement were not significantly different between routes of administration. End-systolic volume was the only echocardiographic parameter significantly affected by IV sedation.

CLINICAL RELEVANCE

Sedation quality was most consistent via IV administration at 15 mg/kg, and minimal changes in cardiac function were observed.

A Critical Review on the Pharmacodynamics and Pharmacokinetics of Non-steroidal Anti-inflammatory Drugs and Opioid Drugs Used in Reptiles

Non-steroidal anti-inflammatory drugs (NSAIDs) and opioids are analgesics used for moderate to severe pain in many animals, including reptiles. However, reptilian dosing regimens are often extrapolated from other animal species. This is not ideal as inter- and intra-species variability in physiology may result in varied drug disposition. Therefore, this critical review aims to collate data from pharmacological studies of selected NSAIDs and opioids performed in reptile and provide an analysis and discussion on the existing pharmacodynamic knowledge and pharmacokinetic data of NSAIDs and opioids use in reptiles. Additionally, key pharmacokinetic trends that may aid dosing of NSAIDs and opioids in reptiles will also be highlighted. Most of the existing reports of NSAID used in reptiles did not observe any adverse effects directly associated to the respective NSAID used, with meloxicam being the most well-studied. Despite the current absence of analgesic efficacy studies for NSAIDs in reptiles, most reports observed behavioural improvements in reptiles after NSAID treatment. Fentanyl and morphine were studied in the greatest number of reptile species with analgesic effects observed with the doses used, while adverse effects such as sedation were observed most with butorphanol use. While pharmacokinetic trends were drug- and species-specific, it was observed that clearance (CL) of drugs tended to be higher in squamates compared to chelonians. The half-life (t_1/2) of meloxicam also appeared to be longer when dosed orally compared to other routes of drug administration. This could have been due to absorption-rate limited disposition. Although current data provided beneficial information, there is an urgent need for future research on NSAID and opioid pharmacology to ensure the safe and effective use of opioids in reptiles.

COMPLETE UNILATERAL MAXILLECTOMY IN A COHORT OF FIVE COLOMBIAN BOAS (BOA IMPERATOR)

Five unrelated adult Colombian boas (Boa imperator) presented with a 1- to 3-mon history of unilateral rostral swelling of the maxilla associated with a chronic rubbing against the enclosure's walls. Moderate to severe gingival inflammation and ulceration of the labial mucosa were present at the level of the swelling with tenderness to the touch. Radiography revealed osteolytic or proliferative lesions of the maxillary bone. Chronic maxillary osteomyelitis was diagnosed. Unilateral maxillectomy was performed on each animal under general anesthesia. Local anesthesia was also achieved by infiltrating lidocaine along the medial and lateral aspect of the maxillary gingiva and at the level of the maxillo-ectopterygoid joint. Using a lateral gingival approach, the maxillo-prefrontal, maxillary-palatine, and maxillo-ectopterygoid attachments were transected, and the maxillary bone removed. Histologic examination revealed pyogranulomatous stomatitis and osteomyelitis in all snakes, and presence of intralesional bacteria (n = 3 snakes). Gram-negative bacteria (Chryseobacterium indologenes and Proteus mirabilis) were cultured from the resected tissue of two snakes. One snake suffered from wound dehiscence 5 d postoperatively. All snakes were fed 15 d postoperatively and ingested dead mice without apparent difficulties. One snake was examined 2 mon and 1 yr after surgery, with no evidence of soft tissue or osseous infection and only minor facial scaring; all other snakes were lost to follow-up 15 d after surgery. Unilateral maxillectomy was performed in a cohort of five Colombian boas suffering from maxillary osteomyelitis. This surgical technique should be considered as an alternative to medical treatment in boid snakes.

Pain and Pain Management in Sea Turtle and Herpetological Medicine: State of the Art

Simple Summary

Rescue and rehabilitative medicine of sea turtles must deal with several circumstances that would be certainly considered painful in other species (trauma, situations that require surgery); thus, it would be natural to consider the use of analgesic drugs to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. However, in these animals (as well as in reptiles in general), many obstacles stand in the way of the application of safe and effective therapeutic protocols. It has been demonstrated that, anatomically and physiologically, turtles and reptiles in general must be considered able to experience pain in its definition of an “unpleasant sensory and emotional experience”. Unfortunately, specific studies concerning sea turtles and reptiles on pain assessment, safety, and clinical efficacy of analgesic drugs currently in use (mostly opioids and non-steroidal anti-inflammatory drugs—NSAIDs) are scarce and fragmentary and suffer from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Abstract

In sea turtle rescue and rehabilitative medicine, many of the casualties suffer from occurrences that would be considered painful in other species; therefore, the use of analgesic drugs should be ethically mandatory to manage the pain and avoid its deleterious systemic effects to guarantee a rapid recovery and release. Nonetheless, pain assessment and management are particularly challenging in reptilians and chelonians. The available scientific literature demonstrates that, anatomically, biochemically, and physiologically, the central nervous system of reptiles and chelonians is to be considered functionally comparable to that of mammals albeit less sophisticated; therefore, reptiles can experience not only nociception but also “pain” in its definition of an unpleasant sensory and emotional experience. Hence, despite the necessity of appropriate pain management plans, the available literature on pain assessment and clinical efficacy of analgesic drugs currently in use (prevalently opioids and NSAIDs) is fragmented and suffers from some basic gaps or methodological bias that prevent a correct interpretation of the results. At present, the general understanding of the physiology of reptiles’ pain and the possibility of its reasonable treatment is still in its infancy, considering the enormous amount of information still needed, and the use of analgesic drugs is still anecdotal or dangerously inferred from other species.

Neuraxial administration of morphine combined with lidocaine induces regional antinociception in inland bearded dragons (Pogona vitticeps)

OBJECTIVE

To assess the antinociceptive efficacy and safety of neuraxial morphine in inland bearded dragons (Pogona vitticeps).

ANIMALS

10 healthy adult bearded dragons.

PROCEDURES

Animals were sedated with alfaxalone (15 mg/kg) SC prior to neuraxial injections. In a randomized, blinded, placebo-controlled, crossover design, animals received preservative-free morphine (0.5 mg/kg) combined with lidocaine (2 mg/kg) or lidocaine (2 mg/kg) only (control treatment). For both treatments, saline (0.9% NaCl) solution was used for dilution to a total volume of 0.3 mL/kg. If the initial injection did not result in motor block of the pelvic limbs or cloaca relaxation within 10 minutes, a second injection was performed. Measurements consisted of bilateral mechanical stimulation of the limbs and at 25%, 50%, and 75% of the trunk's length as well as cloacal tone to assess spread and duration of motor block. Pelvic limb withdrawal latencies in response to a thermal noxious stimulus were measured over a 48-hour period to assess antinociception.

RESULTS

Success rate following the first injection was 90% (18/20 injections) and increased to 100% following a second injection. Motor block occurred within 5 minutes with both treatments. Pelvic limb withdrawal latencies were significantly prolonged following neuraxial morphine versus control treatment for at least 12 hours after injection. By 24 hours, no effect of morphine on pelvic limb latencies was detectable.

CLINICAL RELEVANCE

These results demonstrated that neuraxial administration of morphine results in regional antinociceptive effects for at least 12 hours and has no clinically relevant adverse effects in healthy bearded dragons. This technique has potential for providing regional analgesia in this 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.

Comparison of Thermal and Mechanical Noxious Stimuli for Testing Analgesics in White's Tree Frogs (Litoria caerulea) and Northern Leopard Frogs (Lithobates pipiens)

Determining the clinical efficacy of analgesic drugs in amphibians can be particularly challenging. The current study investigated whether a thermal nociceptive stimulus is useful for the evaluation of analgesic drugs in 2 amphibian species. The objectives of this study were 2-fold: 1) compare 2 models of nociception (thermal and mechanical) using 2 frog species; White's Tree Frogs (Litoria caerulea; WTF) and Northern Leopard Frogs (Lithobates pipiens; NLF) after administration of saline or morphine sulfate; and 2) evaluate antinociceptive efficacy of morphine sulfate at 2 doses in a common amphibian research species, the NLF, using a mechanical stimulus. Neither WTF nor NLF displayed consistent drug-dependent changes in withdrawal responses to a noxious thermal stimulus applied using the Hargreaves apparatus, but NLF exposed to the noxious mechanical stimulus demonstrated a significant dose-dependent antinociceptive response to morphine sulfate. These results indicate that morphine is not antinociceptive in WTF, supporting previously reported results, and demonstrate the importance of using an appropriate experimental antinociceptive test in amphibians. Our data suggest that nociception in amphibian species may be best evaluated by using mechanical nociceptive models, although species differences must also be considered.

Analgesic Efficacy of Tramadol and Morphine in White's Tree Frogs (Litoria caerulea)

Published data are sparse regarding the recognition of clinically relevant pain and appropriate analgesia in amphibians. The amphibian analgesia literature has primarily focused on nociceptive pathways in a single species, the northern leopard frog (Rana pipiens). The objective of the current study was to assess the analgesic efficacy and safety of oral tramadol and subcutaneous morphine in a commonly maintained zoo and pet species, White's tree frog (Litoria caerulea). We hypothesized that tramadol and morphine would provide dose-dependent antinociception, as measured by significant increases in hindlimb withdrawal latency after exposure to a noxious thermal stimulus. Two randomized, placebo-controlled, complete crossover studies were performed, with tramadol (n = 12) administered at 15, 25, and 40 mg/kg PO and morphine (n = 12) administered at 5 and 10 mg/kg SC. Hindlimb withdrawal latency was measured for a maximum of 72 h. No adverse side effects or signs of sedation were observed with any dose or drug evaluated. No significant difference in withdrawal latency was detected between the control and either tramadol or morphine. These negative results were surprising, suggesting that the thermal nociceptive model may not be biologically relevant in amphibian species.

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.

Respiratory and antinociceptive effects of dexmedetomidine and doxapram in ball pythons (Python regius)

OBJECTIVE

To determine the effects of dexmedetomidine, doxapram, and dexmedetomidine plus doxapram on ventilation ([Formula: see text]e), breath frequency, and tidal volume (Vt) in ball pythons (Python regius) and of doxapram on the thermal antinociceptive efficacy of dexmedetomidine.

ANIMALS

14 ball pythons.

PROCEDURES

Respiratory effects of dexmedetomidine and doxapram were assessed with whole-body, closed-chamber plethysmography, which allowed for estimates of [Formula: see text]e and Vt. In the first experiment of this study with a complete crossover design, snakes were injected, SC, with saline (0.9% NaCl) solution, dexmedetomidine (0.1 mg/kg), doxapram (10 mg/kg), or dexmedetomidine and doxapram, and breath frequency, [Formula: see text]e, and Vt were measured before and every 30 minutes thereafter, through 240 minutes. In the second experiment, antinociceptive efficacy of saline solution, dexmedetomidine, and dexmedetomidine plus doxapram was assessed by measuring thermal withdrawal latencies before and 60 minutes after SC injection.

RESULTS

Dexmedetomidine significantly decreased breath frequency and increased Vt but did not affect [Formula: see text]e at all time points, compared with baseline. Doxapram significantly increased [Formula: see text]e, breath frequency, and Vt at 60 minutes after injection, compared with saline solution. The combination of dexmedetomidine and doxapram, compared with dexmedetomidine alone, significantly increased [Formula: see text]e at 30 and 60 minutes after injection and did not affect breath frequency and Vt at all time points. Thermal withdrawal latencies significantly increased when snakes received dexmedetomidine or dexmedetomidine plus doxapram, versus saline solution.

CONCLUSIONS AND CLINICAL RELEVANCE

Concurrent administration of doxapram may mitigate the dexmedetomidine-induced reduction of breathing frequency without disrupting thermal antinociceptive efficacy in ball pythons.

The Use of Self-Inflating Hygroscopic Tissue Expanders to Facilitate Osteosarcoma Removal in a Massasauga Rattlesnake (Sistrurus catenatus)

A 0.34 kg adult female Massasauga rattlesnake (Sistrurus catenatus) was presented for evaluation of a subcutaneous mass affecting the ventral scales. The mass was diagnosed as a sarcoma via punch biopsy with no evidence of metastasis on diagnostic imaging. Surgical margins of 1-2 cm were planned to achieve complete excision of the neoplasm. A technique for tissue expansion was employed due to concerns regarding the ability to close the surgical site without excess tension or dehiscence. Two 27 mm diameter × 5 mm hygroscopic self-inflating tissue expanders were placed subcutaneously under the lateral scales adjacent to the mass. Maximum skin expansion occurred over a four-week period, and no direct negative effects were noted. Excision of the primary mass was performed routinely five weeks after implant placement. Primary closure of the defect was achieved with minimal tension by incorporating the expanded skin. While the surgery was successful with no evidence of metastasis, the snake died of sepsis two weeks postoperatively. This is the first report of the use of self-inflating hygroscopic tissue expanders to help close a surgical defect in a reptile.

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.

Antinociceptive efficacy and respiratory effects of dexmedetomidine in ball pythons (Python regius)

OBJECTIVE To determine antinociceptive efficacy, behavioral patterns, and respiratory effects associated with dexmedetomidine administration in ball pythons (Python regius). ANIMALS 12 ball pythons. PROCEDURES Antinociception was assessed by applying an infrared heat stimulus to the cranioventral surface of snakes during 2 experiments. Thermal withdrawal latency was measured at 0, 2, and 24 hours after SC injections of dexmedetomidine (0.1 or 0.2 mg/kg) or saline (0.9% NaCl) solution and at 0 to 60 minutes after injection of dexmedetomidine (0.1 mg/kg) or saline solution. Behaviors were recorded at 0, 2, and 24 hours after administration of dexmedetomidine (0.1 mg/kg) or saline solution. Tongue flicking, head flinch to the approach of an observer's hand, movement, and righting reflex were scored. Respiratory frequency was measured by use of plethysmography to detect breathing-related movements after injection of dexmedetomidine (0.1 mg/kg) or saline solution. RESULTS Mean baseline withdrawal latency was 5 to 7 seconds; saline solution did not alter withdrawal latency. Dexmedetomidine increased withdrawal latency by 18 seconds (0.2 mg/kg) and 13 seconds (0.1 mg/kg) above baseline values at 2 hours. Increased withdrawal latency was detected within 15 minutes after dexmedetomidine administration. At 2 hours after injection, there were few differences in behavioral scores. Dexmedetomidine injection depressed respiratory frequency by 55% to 70%, compared with results for saline solution, but snakes continued to breathe without prolonged apnea. CONCLUSIONS AND CLINICAL RELEVANCE Dexmedetomidine increased noxious thermal withdrawal latency without causing excessive sedation. Therefore, dexmedetomidine may be a useful analgesic drug in ball pythons and other snake species.

The effects of morphine on gas exchange, ventilation pattern and ventilatory responses to hypercapnia and hypoxia in dwarf caiman (Paleosuchus palpebrosus)

Morphine and other opioids cause respiratory depression in high doses and lower the ventilatory responses to hypoxia and hypercapnia in mammals. Recent studies indicate that turtles respond similarly, but although they are used routinely for post-surgical analgesia, little is known about the physiological effects of opioids in reptiles. We therefore investigated the effects of morphine (10 and 20 mg kg^-1) on gas exchange and ventilation in six dwarf caiman (Paleosuchus palpebrosus) using pneumotachography in a crossover design. Intraperitoneal injections of morphine changed the ventilation pattern from a typical intermittent/periodic pattern with a few or several breaths in ventilatory bouts to single breaths and prolonged the apnoea, such that respiratory frequency was depressed, while tidal volume was elevated. Furthermore, the duration of inspiration and especially expiration was prolonged. The resulting decrease in minute ventilation was attended by a lowering of the respiratory exchange ratio (RER) (especially for 20 mg kg^-1 dose) indicating CO₂ retention with a long time constant for approaching the new steady state. The changes in ventilation pattern and gas exchange reached a new stable level approximately 3 h after the morphine injection and did not significantly affect steady state O₂ uptake, i.e. O₂ consumption. As expected, the ventilatory response to 5% O₂ was lower in morphine-treated caimans, but minute ventilation upon exposure to 2% CO₂ did not differ significantly different from control animals.

Evaluation of sedative and antinociceptive effects of dexmedetomidine, midazolam and dexmedetomidine-midazolam in tegus (Salvator merianae)

OBJECTIVE

To evaluate dexmedetomidine, midazolam and dexmedetomidine-midazolam for sedation and antinociception in tegus.

STUDY DESIGN

Prospective, crossover, randomized, blinded study.

ANIMALS

Six healthy tegus (Salvator merianae) weighing 1.6±0.3 kg.

METHODS

Tegus were administered intramuscularly saline (0.5 mL; CON), dexmedetomidine (0.2 mg kg^-1; DX), midazolam (1 mg kg^-1; MZ) and dexmedetomidine-midazolam (same doses; DM). Heart rate (HR) and respiratory frequency (f_R) were recorded before treatment (baseline) and 15, 30 minutes, 1, 2, 3, 4, 6, 8, 12 and 24 hours after the treatments. Sedation scores were recorded according to resistance to manual restraint, posture and response to noxious stimulus, at baseline and 5, 10, 15, 30 minutes, 1, 2, 3, 4, 6, 8, 12 and 24 hours after the treatments. Antinociception was evaluated by measurement of latency of limb withdrawal reflex (LWR) to thermal stimulus, recorded at baseline and 15 minutes, 1, 2, 4, 8, 12 and 24 hours after the treatments.

RESULTS

Lower HR (DX and DM) and f_R (MZ, DX and DM) than CON were measured 15 minutes after the treatment and for up to 6 hours. Sedation was mild to moderate in MZ, deep in DM and absent in DX, although animals showed behavioral changes in DX, with increase in aggressiveness. Median (interquartile range) duration of sedation were 170 (50; 235) minutes in MZ and 230 (115; 235) minutes in DM. Recovery period was prolonged in both treatments, surpassing the duration of the experiment. Higher LWR than CON was detected from 15 minutes until 12 hours in DX and DM.

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam provided sedation without antinociception, and dexmedetomidine provided antinociception without sedation. Drug combination increased the duration of sedation but not antinociception. Due to increased duration of sedation, reversal of effects with flumazenil and atipamezole should be considered after conclusion of clinical procedures.

Pain and Its Control in Reptiles

Reptiles have the anatomic and physiologic structures needed to detect and perceive pain. Reptiles are capable of demonstrating painful behaviors. Most of the available literature indicates pure μ-opioid receptor agonists are best to provide analgesia in reptiles. Multimodal analgesia should be practiced with every reptile patient when pain is anticipated. Further research is needed using different pain models to evaluate analgesic efficacy across reptile orders.

Antinociceptive and respiratory effects following application of transdermal fentanyl patches and assessment of brain μ-opioid receptor mRNA expression in ball pythons

OBJECTIVE To quantify plasma fentanyl concentrations (PFCs) and evaluate antinociceptive and respiratory effects following application of transdermal fentanyl patches (TFPs) and assess cerebrospinal μ-opioid receptor mRNA expression in ball pythons (compared with findings in turtles). ANIMALS 44 ball pythons (Python regius) and 10 turtles (Trachemys scripta elegans). PROCEDURES To administer 3 or 12 μg of fentanyl/h, a quarter or whole TFP (TFP-3 and TFP-12, respectively) was used. At intervals after TFP-12 application in snakes, PFCs were measured by reverse-phase high-pressure liquid chromatography. Infrared heat stimuli were applied to the rostroventral surface of snakes to determine thermal withdrawal latencies after treatments with no TFP (control [n = 16]) and TFP-3 (8) or TFP-12 (9). Breathing frequency was measured in unrestrained controls and TFP-12-treated snakes. μ-Opioid receptor mRNA expression in brain and spinal cord tissue samples from snakes and turtles (which are responsive to μ-opioid receptor agonist drugs) were quantified with a reverse transcription PCR assay. RESULTS Mean PFCs were 79, 238, and 111 ng/mL at 6, 24, and 48 hours after TFP-12 application, respectively. At 3 to 48 hours after TFP-3 or TFP-12 application, thermal withdrawal latencies did not differ from pretreatment values or control treatment findings. For TFP-12-treated snakes, mean breathing frequency significantly decreased from the pretreatment value by 23% and 41% at the 24- and 48-hour time points, respectively. Brain and spinal cord tissue μ-opioid receptor mRNA expressions in snakes and turtles did not differ. CONCLUSIONS AND CLINICAL RELEVANCE In ball pythons, TFP-12 application resulted in high PFCs, but there was no change in thermal antinociception, indicating resistance to μ-opioid-dependent antinociception in this species.

Pharmacokinetic/pharmacodynamic evaluation of grapiprant in a carrageenan-induced inflammatory pain model in the rabbit

Grapiprant is the novel selective EP4 receptor inhibitor recently issued on the veterinary market for dogs affected by osteoarthritis. The aim of this study was twofold: to evaluate the pharmacokinetics and the pharmacodynamics of grapiprant in the induced inflammatory pain model in the rabbit after a single IV injection of 2 mg/kg; to compare the thermal antinociception effect after 2 mg/kg IV grapiprant, with that generated by 0.5 mg/kg meloxicam SC injected. Rabbits (n = 12) were randomly assigned to two crossover studies (single-dose, two-period crossover). The first study group A (n = 3) received a single IV dose of grapiprant at 2 mg/kg dissolved in ethanol. Group B (n = 3) received a single IV injection of ethanol (equivalent volume to grapiprant volume) at the same site. The second study group C (n = 3) received a single SC dose of meloxicam at 0.5 mg/kg. Group D (n = 3) received a single SC injection of 15% ethanol (equivalent volume to grapiprant volume) at the same site. After a 2-week washout period, the groups were rotated and the experiments repeated. Blood samples (0.7 mL) were collected from the right ear artery at assigned times and grapiprant plasma concentrations determined by a validated HPLC-FL method. Three hours prior to administration of the drugs, inflammation was induced by SC injection of lambda carrageenan (200 μL, 3% in physiological saline) under the plantar surface of the right hind paw. At a similar time to the blood collection, an infrared thermal stimuli (40 °C) was applied to the plantar surface of the rabbits' hindlimbs to evaluate the thermal withdrawal latency (TWL). The thermal antinociceptive effect was expressed as maximum possible response (% MPR). Grapiprant plasma concentrations were detectable up to the 10-h time point (concentration range 17-7495 ng/mL). The grapiprant-treated group showed a significant increase in TWL from 1 h and up to 10 h after drug administration compared to the control. In contrast, the meloxicam group showed a significant increase in TWL from 4 up to 10 h after drug administration, compared to control. The maximal MPR% was not statistically different between the grapiprant and meloxicam group from 4 to 8 h, while significant differences were shown at 1, 1.5, 2, 10 and 24 h. Given these findings, grapiprant appears to be an attractive option for antinociception in rabbits, due to its rapid onset and extended duration of effect.

Comparative analgesic efficacy of morphine sulfate and butorphanol tartrate in koi (Cyprinus carpio) undergoing unilateral gonadectomy

OBJECTIVE

To identify pain-related behaviors and assess the effects of butorphanol tartrate and morphine sulfate in koi (Cyprinus carpio) undergoing unilateral gonadectomy. Design-Prospective study.

ANIMALS

90 adult male and female koi.

PROCEDURES

Each fish received saline (0.9% NaCl) solution (which is physiologically compatible with fish) IM, butorphanol (10 mg/kg [4.5 mg/lb], IM), or morphine (5 mg/kg [2.3 mg/lb], IM) as an injection only (6 fish/treatment); an injection with anesthesia and surgery (12 fish/treatment); or an injection with anesthesia but without surgery (12 fish/treatment). Physiologic and behavioral data were recorded 12 hours before and at intervals after treatment.

RESULTS

Compared with baseline values, the saline solution-surgery group had significantly decreased respiratory rates (at 12 to 24 hours), food consumption assessed as a percentage of floating pellets consumed (at 0 to 36 hours), and activity score (at 0 to 48 hours). Respiratory rate decreased in all butorphanol-treated fish; significant decreases were detected at fewer time points following morphine administration. In the butorphanol-surgery group, the value for food consumption initially decreased but returned to baseline values within 3 hours after treatment; food consumption did not change in the morphine-surgery group. Surgery resulted in decreased activity, regardless of treatment, with the most pronounced effect in the saline solution-surgery group. Changes in location in water column, interactive behavior, and hiding behavior were not significantly different among groups. Butorphanol and morphine administration was associated with temporary buoyancy problems and temporary bouts of excessive activity, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Butorphanol and morphine appeared to have an analgesic effect in koi, but morphine administration caused fewer deleterious adverse effects. Food consumption appeared to be a reliable indicator of pain in koi.

Evaluation of the analgesic effects of oral and subcutaneous tramadol administration in red-eared slider turtles

OBJECTIVE

To determine the dose- and time-dependent changes in analgesia and respiration caused by tramadol administration in red-eared slider turtles (Trachemys scripta).

DESIGN

Crossover study.

ANIMALS

30 adult male and female red-eared slider turtles.

PROCEDURES

11 turtles received tramadol at various doses (1, 5, 10, or 25 mg/kg [0.45, 2.27, 4.54, or 11.36 mg/lb], PO; 10 or 25 mg/kg, SC) or a control treatment administered similarly. Degree of analgesia was assessed through measurement of hind limb thermal withdrawal latencies (TWDLs) at 0, 3, 6, 12, 24, 48, 72, and 96 hours after tramadol administration. Nineteen other freely swimming turtles received tramadol PO (5, 10, or 25 mg/kg), and ventilation (V(E)), breath frequency, tidal volume (V(T)), and expiratory breath duration were measured.

RESULTS

The highest tramadol doses (10 and 25 mg/kg, PO) yielded greater mean TWDLs 6 to 96 hours after administration than the control treatment did, whereas tramadol administered at 5 mg/kg, PO, yielded greater mean TWDLs at 12 and 24 hours. The lowest tramadol dose (1 mg/kg, PO) failed to result in analgesia. Tramadol administered SC resulted in lower TWDLs, slower onset, and shorter duration of action, compared with PO administration. Tramadol at 10 and 25 mg/kg, PO, reduced the V(E) at 12 hours by 51% and 67%, respectively, and at 24 through 72 hours by 55% to 62% and 61 % to 70%, respectively. However, tramadol at 5 mg/kg, PO, had no effect on the V(E).

CONCLUSIONS AND CLINICAL RELEVANCE

Tramadol administered PO at 5 to 10 mg/kg provided thermal analgesia with less respiratory depression than that reported for morphine in red-eared slider turtles.

Tramadol use in zoologic medicine

Numerous analgesics are available for use in animals, but only a few have been used or studied in zoologic species. Tramadol is a relatively new analgesic that is available in an inexpensive, oral form, and is not controlled. Studies examining the effect of tramadol in zoologic species suggest that significant differences exist in pharmacokinetics parameters as well as analgesic dynamics. This article reviews the current literature on the use of tramadol in humans, domestic animals, and zoologic species.

Clinical interpretation of pharmacokinetic and pharmacodynamic data in zoologic companion animal species

The treatment and prevention of pain in zoologic companion animals is difficult because of the lack of data available on the safety and efficacy of analgesics. Pharmacokinetic (PK)-pharmacodynamic (PD) studies integrate changes in drug concentrations and changes in the drug's effect. All experimental studies assessing the PDs of analgesics have limitations in animals, but the data provided by experimental studies are valuable in designing dosages. Placebo-controlled, randomized, and blinded clinical trials provide the best PK and PD data, but are rarely performed in major veterinary species because of the number of animals required for the study, lack of preliminary PK and PD data in a given species, species-specific differences in PK and PD, and ethical and toxicologic concerns. The usefulness and limitations as well as considerations for interpreting PK, PD, and controlled clinical studies are discussed. An example of allometric analysis of buprenorphine in mammals is also included.

Reptile diagnostic endoscopy and endosurgery

The 2.7-mm telescope commonly used in avian practice has transitioned into an invaluable diagnostic tool for the reptile clinician. Previously plagued by vague medical histories, nonpathognomonic physical examinations, indistinct diagnostic images, and less than conclusive clinical pathology results, the reptile clinician often has had trouble making a definitive, antemortem diagnosis. A definitive diagnosis generally relies on the demonstration of a host pathologic response and the causative agent. The ability to examine internal structures and collect biopsies has enabled many postmortem diagnoses to now be appreciated in the living animal, and along with accurate diagnosis comes accurate prognosis and improved case management. The advent of 3-mm human pediatric laparoscopy equipment has fueled interest in minimally invasive endosurgery in exotic pets, including reptiles. However, the chelonian shell has also served as a catalyst to speed the development of surgical approaches to the coelom that do not involve major shell surgery. This article summarizes the most common endoscopic approaches in lizards, chelonians, and snakes for the purposes of making a diagnosis and increasingly performing endosurgery.

Effects of opioid receptor activation on thermal antinociception in red-eared slider turtles (Trachemys scripta)

OBJECTIVE

To determine the effects of mu-, delta-, and kappa-opioid receptor (MOR, DOR, and KOR, respectively) activation on thermal antinociception in red-eared slider turtles Trachemys scripta.

ANIMALS

51 adult turtles.

PROCEDURES

Infrared heat stimuli were applied to the plantar surface of turtle hind limbs. Thermal hind limb withdrawal latencies (HLWLs) were measured before (baseline) and at intervals after SC administration of various doses of saline (0.9% NaCl) solution (SS), MOR, DOR, or KOR agonists (3 to 13 turtles/treatment). Treatment with a DOR antagonist SC prior to DOR agonist administration was also evaluated.

RESULTS

Treatment with an MOR agonist ([D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin acetate salt [DAMGO; 1.3 or 6.6 mg/kg]) increased HLWLs (from baseline) at 2 to 8 hours after injection; at the higher dose, the maximum mean increase was 5.6 seconds at 4 hours. Treatment with a DOR agonist ([D-Ala(2), D-Leu(5)]-enkephalin acetate salt [DADLE; 25 mg/kg]) increased mean HLWL by 11.3 seconds at 4 hours; however, treatment with DADLE (5.8 mg/kg) or with another DOR agonist ([D-Pen(2),(5)]-enkephalin hydrate [DPDPE; 1.2 or 6.3 mg/kg]) did not alter HLWL, compared with SS effects. Administration of a DOR antagonist (naltrindole hydrochloride; 10 mg/kg) prior to DADLE administration (25 mg/kg) increased mean HLWL by 2.7 seconds at 4 hours. One KOR agonist, U50488 ([-]-trans-[1S,2S]-U50488 hydrochloride hydrate; 6.7 mg/kg) decreased HLWL steadily from 2 to 24 hours (less than baseline value); another KOR agonist, U69593 ([+]-[5alpha,7alpha,8beta]-N-Methyl-N-[7-{1-pyrrolidinyl}-1-oxaspiro{4.5}dec-8-yl]-benzene-acet-amide; 6.7 or 26 mg/kg) did not alter HLWLs, compared with SS effects.

CONCLUSIONS AND CLINICAL RELEVANCE

Opioid-dependent thermal antinociception in turtles appeared to be attributable mainly to MOR activation with a relatively minor contribution of DOR activation.