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An Urban Experience
depression, and reduced gastrointestinal motility. It should be noted, however, that pain in itself can also result in respiratory depression, abnormal behavior, depressed food intake, and ileus. The use of opioids should therefore not be withheld in any animal which is experiencing pain.
Buprenorphine is a full μ-opioid receptor agonist with potent analgesic actions. It is thought to have less side effects, such as respiratory depression, nausea and dysphoria, compared to the other opioids. Profound sedation may be seen at doses greater than 20 μg/
kg. The duration of action may vary from 6 to 12 hours. Before giving the next dose, it is advised to re-assess the animal to identify whether sedative effects or negative side effects are encountered. Based on these findings the subsequent dose can be adjusted.
Butorphanol also provides analgesia in several exotic companion mammal species. It is assumed that butorphanol has agonistic effects on μ- δ- and κ-opioid receptor with the highest affinity for the κ-opioid receptor. Its clinical effects seem similar to buprenorphine. The duration of its analgesic actions, however, is significantly shorter. It also has a greater sedative effect and potentially results in more respiratory suppression.
Fentanyl, a short acting and very potent μ-opioid receptor agonist with potent analgesic actions can be used as a constant rate infusion (CRI). Fentanyl CRI is most often used during surgery and in the post-operative period. Respiratory depression is a potential serious side effect warranting frequent assessment of the ventilatory status of these patients.
Tramadol is not a typical opioid, with effects on the μ-opioid receptor, the serotonin-, the catecholamine- and the GABA-system. Palatability of tramadol is a significant problem in rabbits. In ferrets, palatability issues have
not been reported. During a pharmacokinetic study in rabbits, a dose of 11 mg/kg did not result in plasma concentrations considered analgesic in people. No pharmacokinetic data are available in ferrets, but a dose of 10 mg/kg once daily has been suggested. Tramadol cannot be used in chinchillas as levels which may be analgesic will result in severe neurological signs.
Local anesthetics and locoregional techniques
The use of local anesthetics, e.g. bupivacaine and lidocaine, can be very effective in preventing stimuli reaching the spinal cord and are very useful additions in a pain management plan. The good predictability of drug effect with respect to both desired and unwanted side effects of local anesthetics, together with insensitivity
to species specific physiology makes locoregional techniques an excellent choice. Techniques that can be used are incisional line blocks, local infiltration, ring blocks, splash-blocks, topical application, conductive nerve block and epidural anesthesia. Care must be
taken not to exceed maximum doses which need to be calculated beforehand, often requiring diluting the drug to obtain an adequate volume. Maximum doses are 1 to 2 mg/kg whereby it is important to realize that bupivacaine is twice as potent as lidocaine. Adding opioids such as morphine or buprenorphine to a local block can increase the duration of analgesia significantly.
Dental blocks are well described in rabbits and ferrets. These included the infraorbital nerve block, mental nerve block, mandibular nerve block and the maxillary nerve block. Intra-testicular blocks are also described. Allow at least 5 minutes for the local anesthetic to be fully effective.
Although a lot of data on clinical efficacy, pharmacokinetics and pharmacodynamics of analgesic drugs and specific behaviors related to pain are lacking in exotic companion mammal species, pain management does not really differ between species. Analgesic treatment is a dynamic, practical and subjective
process. Therefore ‘clinical experience’ from colleagues and appropriate training in pain physiology and pain management is at least as valuable as ‘hard scientific’ data. People are therefore encouraged to maintain adequate record keeping and follow up, in addition to reporting on clinical experience with analgesics in rabbits and ferrets until more scientific evidence is available.
References for further reading
• Barter LS. Rabbit analgesia. Veterinary Clinics of North America: Exotic Animal Practice. 2011 Jan 31;14(1):93-104.
• van Oostrom H, Schoemaker NJ, Uilenreef JJ. Pain management in ferrets. Veterinary Clinics of North America: Exotic Animal Practice. 2011 Jan 31;14(1):105-16.
• Johnson AG, Day RO. The problems and pitfalls of NSAID therapy in the elderly (Part I). Drugs & aging. 1991 Mar 1;1(2):130-43.

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