Page 47 - BSAVA Guide to Pain Management in Small Animal Practice

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Pharmacological

treatment of pain

In recent years there has been increased and spinal cord, and sometimes elsewhere, for
recognition of the importance of analgesia for example in joints, where receptors are
veterinary patients. This has been accompanied upregulated in response to in ammation. here
by the development and licensing of several are three main types of opioid receptors: the
analgesic drugs for veterinary use. There is a delta (DOP), the kappa (KOP), and the mu opioid
good evidence base regarding the use, safety peptide receptors (MOP). The most important
and e cacy of licensed drugs; research into type for analgesia is the MOP receptor. Opioid
non-licensed drugs, which may be used receptors are situated both pre- and post-
according the Cascade, continues. Veterinary synaptically, for example, in the dorsal horn of
surgeons (veterinarians), therefore, have a the spinal cord. Agonism of an opioid receptor
relatively wide range of treatment options to results in hyperpolarization of the neurone,
prevent and alleviate pain. which decreases cell excitability, reducing
propagation of the action potential and onward
neurotransmitter release.
Analgesia use in practice
Opioids Metabolism and excretion
Most opioids are metabolized by the liver, the
Opioids are widely used in human and exception being remifentanil, which has a very
veterinary practice to provide analgesia. short duration of action due to metabolism by
Although they have many side e ects, these are esterase enzymes in plasma. Some opioids have
rarely signi cant in veterinary patients, so active metabolites and the analgesic e ect may
opioids are usually safe even for sick animals. depend on hepatic biotransformation; for
example, in humans much of the analgesic
Mechanism of action e ect of morphine is due to one of its
Opioids act on opioid peptide receptors, which metabolites, morphine 6 glucuronide. he
are part of the endogenous endorphin/ duration of action of opioids may be increased in
enkephalin-mediated analgesia system. animals with hepatic dysfunction so the dosing
Analgesia is mediated by receptors in the brain interval should be increased (based on

42 BSAVA Guide to Pain Management in Small Animal Practice. Edited by Ian Self. ©BSAVA 2019

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