Abstract

Veterinarians that treat exotic species are becoming more aware of the need for analgesia; however, analgesics are often not provided or considered in primary treatment for reptiles and amphibians. These species have the neurologic components, antinociceptive mechanisms and behavioral responses to pain that are similar to those seen in domestic animals and humans. Preemptive analgesia, multimodal therapy and contraindications for use of certain analgesics are addressed as well as behaviors and disease processes that can be associated with pain in reptiles and amphibians.

Introduction

Pain management has become an integral part in providing optimal medical and surgical care for all patients and should be considered in the primary treatment of reptiles and amphibians as well. Many practitioners do not provide pain management in these species because of the lack of familiarity of drug choices and practical guidelines for their administration. The fear of potential side effects and the inability to recognize the behaviors associated with pain also play a major role in why analgesia is often not a part of routine therapy.

Reptiles and amphibians have the same or similar neurologic components to perceive pain that are found in dogs, cats, and other domestic species.¹⁶ Antinociceptive mechanisms to modulate pain are also present and they display appropriate behavior in response to stimuli that are known to be painful in other species.¹⁶

The physiologic “stress response” to pain in reptiles and amphibians is also similar to other species. It can include vasoconstriction, increased heart rate and stroke volume, decreased gastrointestinal and urinary tone, and endocrine responses leading to a catabolic state with decreased kidney function.¹⁷ Nociceptive stimulation of the brain also enhances reflex sympathetic responses, which create increased blood viscosity, prolonged clotting time, fibrinolysis, and platelet aggregation.¹⁷

Clinically, in all exotic species, the response to pain can include immune suppression, impaired wound healing, decreased food and water intake,¹⁴ and secondary medical problems including gastric ulcers, gastrointestinal stasis, shock, and even death. These responses make it important for practitioners to reevaluate the need for analgesia in reptiles and amphibians that are experiencing trauma, disease, surgery, or other invasive procedures in which pain is a known component.

Recommendations Concerning Analgesics for Reptiles and Amphibians

If possible, analgesics should be provided before a painful stimulus occurs. Providing preemptive analgesia helps decrease postoperative pain including that caused by both neuropathic pain and inflammatory pain.¹⁴ Neuropathic pain occurs when pulling and stretching of tissues during surgery triggers nociceptive nerve endings causing central nervous system changes to occur that enhance pain postoperatively. Handling and crushing of tissues causes inflammation that also increases postoperative pain. By providing preemptive analgesia, the dose needed for maintenance anesthesia is decreased. Therefore, when using injectable anesthesia, the anesthetic doses should be adjusted accordingly.

Combining different classes of analgesics to manage pain, known as multimodal therapy, is also recommended. In each painful situation, numerous pain pathways would stimulate different neurotransmitters. Providing multiple analgesics, that would address the different pathways, can have a synergistic effect and the analgesics can be used at lower doses when used together, often with less side effects.¹⁴ Each patient should be treated as an individual when deciding what analgesics will be used and evaluated for the need to add to or alter treatment based on its clinical response to the regimen provided.

Care should be taken when using analgesics under certain circumstances in all species. For instance, when bleeding disorders, enteritis, gastritis, gastric ulcers, hepatic impairment, renal impairment, hypotension, hypovolemia or a potential for hypotension during surgery exist, nonsteroidal anti-inflammatory drugs (NSAIDs) should not be used or used judiciously.¹⁴ As with other species, two or more NSAIDs should not be used concurrently.¹³ Avoid prolonged use of NSAIDs and it has been suggested to administer sucralfate (especially in herbivores) to those patients kept on NSAIDs for chronic pain.³

Opioid analgesics have a relatively short duration of action, which should be considered when determining the frequency of administration. They should also be avoided in hypotensive patients and the use of opioids decreases the dose needed for isoflurane anesthesia. If injectable anesthesia is used, it is recommended to administer opioids when the patient is at a lighter plane of anesthesia to prevent overdose.

Behaviors Associated with Pain

Practitioners need to become familiar with normal behaviors of each species that they treat in order to recognize painful behaviors as early as possible. Identification of pain in all prey species is made more difficult because they exhibit less overt pain-associated behaviors in order to decrease their chances of being recognized as ill by predators.¹⁰ Also, due to the same survival instincts, immobility is a common behavior seen in prey species that are presented for examination, making it more difficult to determine if pain is present.⁶ Nocturnal species present more of a challenge, as the diurnal observation of their behaviors, when presented for examination, may result in inaccurate assessment.⁶

Many of the behaviors presented below can also be seen in any patient that is ill, but pain should be considered as a potential component in the disease process if these behaviors are present. Also, never discount the pet owner’s assessment of pain and anxiety in their pet, as they may be the most in tuned to what normal behavior is for that animal.

Behaviors Associated with Pain in Reptiles and Amphibians

Reptiles - Lizards

Reptiles - Snakes

Reptiles - Chelonians

Amphibians

Painful Disease Processes

Cooling or freezing reptiles and amphibians to produce immobility, anesthesia or euthanasia is not acceptable or humane as it creates decreased nociceptive threshold and increased sensitivity to pain.^1,5,11

Analgesic Dosages for Reptiles and Amphibians

Formularies that provide analgesic dosages for exotic species attempt to provide dosages that have been found to be safe for those species, some have pharmacokinetic origins but most are derived empirically. Individual reptile species need different analgesic dosages—lizards, snakes, chelonians, and amphibians have different needs from each other. No one dose could satisfy the idiosyncrasies of each species, let alone each patient. Relative health or debilitation of the patient also must be taken into consideration when deciding on a dose. The dosages provided in this paper include broad ranges to reflect those individualities. It is, therefore, important for practitioners to have multiple exotic animal reference formularies available that allow them to make the best decisions for each patient that they treat.

Analgesics for Reptiles and Amphibians

Reptiles

NSAIDs

Carprofen—2–4 mg/kg initially followed by 1–2 mg/kg q 24–72 h IV, IM, PO, SC
Flunixin meglumine—0.1–1.0 mg/kg q 12–24 h IV, IM (for 2 to 3 days)
Ketoprofen—2 mg/kg IM, SC q 24–48 h
Meloxicam—0.1–0.2 mg/kg q 24 h PO

Opioids

Buprenorphine HCl—0.01 mg/kg q12 h IM
Butorphanol tartrate—0.05–1 mg/kg q 12 h IM, IV, PO, SC (up to 25 mg/kg in tortoises)
Morphine—0.3–4.0 mg/kg q12–24 h ICo (intracoelomic), IM, SC

Amphibians

Opioids

Buprenorphine HCl—35–75 mg/kg q 12 h IM
Butorphanol tartrate—0.05–1.0 mg/kg q 12 h IM, IV, PO, SC
Morphine—20–160 mg/kg SC, IM, topical

References are available for formularies containing dosages and recommendations for specific species as doses vary greatly between different species.^{2,4,7-9,12,13,15}

Alternative Approaches to Pain Management

Little work has been done on alternative approaches to pain management in reptiles and amphibians. Other therapies exist that aid in treatment of both acute and chronic pain including acupuncture, massage therapy, magnetic therapy, chiropractic, and physiotherapy.

Conclusions

As with all species, a return to normal behavior indicates a positive response to analgesic treatment. For reptiles and amphibians, this includes eating, drinking, and defecating, as well as the resumption of normal postures and behaviors. Until further studies are done to elucidate pain perception and response in reptiles and amphibians, any disease or process that has pain as a known component in other species should be considered painful in these species as well and treated accordingly.

Literature Cited

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