Introduction

Opioids

• Produce very effective analgesia and safe if the appropriate dose is used.
• Action probably produced by mimicking the endogenous opiates at receptors in the central nervous system which modify the perception of pain, being transmitters in inhibitory pathways, and at opiate receptors expressed at the periphery in inflammatory states.
• Formerly not in widespread use due to fear of producing 'maniacal excitement' in the cat. This effect is only seen at high doses greatly in excess of what is required to produce effective analgesia.
• Cause significant respiratory depression in man, this is insignificant in other animals at clinical dose rates, except when combined with other respiratory depressive agents.
• Cause some sedation, synergistic effect with sedatives such as acepromazine Acepromazine maleate.
• Cats with CNS trauma may respond unpredictably to opioids   →   monitor ventilatory status closely as any respiratory depression may increase intracranial pressure.
• Use lower doses in very old, very young cats and those with liver disease as hepatic clearance is slowed.
• Many are Schedule 3 drugs, subject to strict regulation of their purchase, storage and use.
• Tolerance and dependence develop with prolonged administration.

Pure opioid agonists

• Predictable analgesic effect directly related to dose.
• High maximum efficacy.
• If the stated dose is given and not found to be effective then the dose can be repeated safely until analgesia is attained.

Analgesic drugs

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Steagall P V, Taylor P M, Rodrigues L C et al (2009) Analgesia for cats after ovariohysterectomy with either buprenorphine or carprofen alone or in combination. Vet Rec 164 (12), 359-363 PubMed.
• Steagall, P V, Carnicelli P, Taylor P M et al (2006) Effects of subcutaneous methadone, morphine, buprenorphine or saline on thermal and pressure thresholds in cats. J Vet Pharmacol Ther 29 (6), 531-537 PubMed.
• Möllenhoff A, Nolte I & Kramer S (2005) Anti-nociceptive efficacy of carprofen, levomethadone and buprenorphine for pain relief in cats following major orthopaedic surgery. J Vet Med A Physiol Clin Med 52 (4), 186-198 PubMed.
• Robertson S A, Taylor P M (2004) Pain management in cats-past, present and future. Part 2. Treatment of pain-control pharmacology. J Feline Med Surg 6 (5), 321-333 PubMed.
• Johnson C (1999) Chemical restraint in the dog and cat. In Practice 21 (3), 111-118 VetMedResource.
• Lascelles B D, Waterman A (1997) Analgesia in cats. In Practice 19 (4), 203-213 VetMedResource.
• Taylor P M (1985) Analgesia in the dog and cat. In Practice 7 (1), 5-13 VetMedResource.

Other sources of information

• Hall L W and Taylor P M (1994) Eds Anaesthesia of the Cat.London: Bailliere Tindall. pp112-113, 116-118, 120-128. ISBN 0 7020 1665 9
• Nolan A M (1989) Analgesia. In: Manual of Anaesthesia for Small Animal Practice. Ed A D R Hilbery. Cheltenham: British Small Animal Veterinary Association. pp33-38. ISBN 0 905214 09 9.