Equis ISSN 2398-2977

Anesthesia: analgesia - opioid

Contributor(s): Glen Pettifer, Mark Senior

Introduction

  • Almost throughout all of recorded history the opium poppy ( Papaver somniferum) has been used to provide pain relief in one form or another. Despite the development of a wide range of naturally occurring and synthetic opioids, in many cases, morphine continues to be the mainstay of analgesic therapy for the treatment of severe pain in both human and veterinary medicine.
  • The use of opioids in horses is a matter of some discussion and occasional controversy. Continued research into the role of opioids in the treatment of equine pain is needed.

Opiate

  • Drugs derived from the opium poppy, eg morphine, papaveretum and codeine.

Narcotic

  • Any drug that produces insensibility or stupor.

Opioids

  • Strictly defined, an opioid is a synthetic narcotic that has opiate-like activity but is not derived from opium. Opioid is frequently used to describe any drug with opiate-like activity.
  • Narcotic analgesicsare opioids that provide analgesia but also induce a state of sedation or euphoria (a sense of well-being) called narcosis.
  • Opioids exert their effects by binding to opioid receptors.
  • Originally it was thought that opioid receptors could only be found in the brain and the spinal cord. Subsequent research has identified opioid receptors in the periphery, eg gastrointestinal tract, cornea, dental tissue and joints. The population of peripheral opioid receptors is fluid and increases in conditions of inflammation.
  • Opioid receptor distribution in the CNS and the effects of these receptors differs between species (and probably individuals). In humans µ agonists tend to cause narcosis whereas in horses they may be associated with an increase in locomotor activity and excitement.

Receptor types

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Side effects

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Classification of opioids

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Clinical use of opioids

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Metabolism

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Further Reading

Publications

Refereed papers
  • Recent references fromPubMed.
  • Michou J & Leece E (2012)Sedation and analgesia in the standing horse 2. Local anaesthesia and analgesia techniques. In Pract34(10), 578-587.
  • Mircica E, Clutton R E, Kyles K W & Blissitt K J (2003)Problems associated with perioperative morphine in horses: a retrospective case analysis. Vet Anaesth Analg30(3),147-155PubMed.
  • Maxwell L K, Thomasy S M, Slovis N & Kollias-Baker C (2003)Pharmacokinetics of fentanyl following intravenous and transdermal administration in horses. Equine Vet J35(5), 484-490PubMed.
  • Steffey E P, Eisele J H & Baggot J D (2003)Interactions of morphine and isoflurane in horses. Am J Vet Res64(2), 166-175PubMed.
  • Bennett R C & Steffey E P (2002)Use of opioids for pain and anesthetic management in horses. Vet Clin North Am Equine Pract18(1), 47-60PubMed
  • Dodman N H, Shuster L, Court M H & Dixon R (1987)Investigation into the use of narcotic antagonists in the treatment of a stereotypic behavior pattern (crib-biting) in the horse. Am J Vet Res48(2), 311-319PubMed.
  • Kalpravidh M, Lumb W V, Wright M & Heath R B (1984)Analgesic effects of butorphanol in horses: dose-response studies. Am J Vet Res45(2), 211-216PubMed.
  • Kalpravidh M, Lumb W V, Wright M & Heath R B (1984)Effects of butorphanol, flunixin, levorphanol, morphine, and xylazine in ponies. Am J Vet Res45(2), 217-223PubMed.


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