Plasma Fentanyl Concentrations Achieved after Transdermal Fentanyl Patch Application in Prehensile-Tailed Skinks, Corucia zebrata

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.

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.

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.

Aspects in controlled drug delivery for topical applications in veterinary medicine

The controlled release of drugs is an appealing area of research as it provides numerous benefits in veterinary and human medicine. In this paper we attempt to analyze certain aspects related to topical drug delivery systems, their successes and failures, and their place in veterinary medicine. Some emphasis is given to the pharmaceutical aspects of the delivery systems, where the material available made it possible. Purely topical devices, such as cattle ear tags and various collars, as well as some topically administered bioavailable delivery systems are discussed. Special attention is given to hitherto under-evaluated delivery systems, such as topical varnishes. A carefully selected bibliography aims to lead the reader easily to the facts, without providing overwhelming data of varying quality. We believe that the paper may be of interest to practicing veterinarians as well as to pharmaceutical scientists working or considering practice in the area.

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.