Page 52 - BSAVA Guide to Pain Management in Small Animal Practice

5 | Pharmacological treatment of pain

VetBooks.ir Activity at receptor Comments Examples Receptor

Drug
Full agonist ose dependent e ect aximal e ect achieved at high Fentanyl MOP
high e cacy dose
Suitable for treating moderate
to severe pain
Partial agonist ose dependent e ect to aximal e ect is never Buprenorphine MOP
low e cacy a certain dose achieved despite increased
Acts as agonist and dose
antagonist at the same Suitable for treating mild to
receptor type moderate pain
Antagonist No e ect Competes with agonist at Naloxone MOP
receptor resulting in reversal
antagonism of agonist e ect
Mixed Agonist at one receptor Can be used to reverse Butorphanol KOP (agonist),
agonist/ type, antagonist at antagoni e e ects at one MOP
antagonist another receptor type receptor type while still (antagonist)
exerting an e ect at a di erent
receptor type
Classi cation of drugs acting on opioid receptors. P kappa opioid peptide receptor; P mu
opioid peptide receptor.

The term ‘potency’ can cause confusion. It ■ Likely degree of pain experienced by the
refers to the dose of a drug needed to achieve a animal
desired e ect. or example, a commonly used ■ Likelihood of adverse e ects
analgesic dose of buprenorphine is . mg ■ Concurrent illness.
kg. The same dose of methadone is unlikely to
alleviate pain, approximately ten times the dose Pre-anaesthetic medication
would be needed for this about . mg kg Opioids may be combined with other sedatives
methadone). This means that buprenorphine is such as aceproma ine, alpha agonists and
more potent than methadone, but it does not benzodiazepines in pre-anaesthetic medication
mean that buprenorphine provides better for any procedure. They are particularly useful for
analgesia than methadone. In fact, since painful procedures or when pain due to
methadone is a full MOP agonist and pre-existing conditions is likely, for example,
buprenorphine is a partial MOP agonist, better radiography of a patient with osteoarthritis. For
analgesia is likely to be achieved using geriatric or sick patients (for whom the cardio-
methadone when appropriate doses are used vascular e ects of aceproma ine or alpha
methadone has higher e cacy . agonists are undesirable) they can be used as
the sole pre-anaesthetic agent. They enhance
Clinical use of opioids the sedative e ect of the other drugs, reduce
actors in uencing drug choice include injectable and inhalant anaesthetic require-
ments, and provide pre-emptive analgesia.
■ Availability
■ Licensing Intraoperative analgesia
■ Familiarity The opioid used as part of the pre-anaesthetic
■ Patient history (previous opioid use) medication may be adequate for intraoperative
■ Suitability for chosen route of administration analgesia, especially if used as part of a
■ Dosing interval/suitability for intravenous multimodal analgesia strategy. However,
infusion additional opioids may be required during the

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