Opioid Analgesia in Horses

Abstract

Opioid analgesics have been the foundation of human pain management for centuries, and their value in animals has increased since it was proposed that it is the veterinarian's duty to alleviate pain whenever it may occur. Compared with other domesticated species, the horse has benefitted less from the increased understanding of opioid pharmacology in animals, because early literature was overlooked and later work, which examined adverse side effects rather than analgesia, concluded that analgesic and excitatory doses were irreconcilably close. More recent studies have indicated a widening role for opioid analgesics in equine pain management, and radioligand studies have revealed a basis for the equine response pattern to opioid analgesics.

Postcastration analgesia in ponies using buprenorphine hydrochloride

“…Two of the ponies that received buprenorphine showed some signs of this although it was not a serious problem; the walking was not manic or uncontrollable. Opioid-related ‘excitement’ is more likely in pain-free horses (Clutton 2010), and one of the affected ponies in this study had not undergone surgery, so was presumably more susceptible to this opioid side effect. None of the ponies that received buprenorphine as rescue analgesia exhibited signs of locomotor stimulation or excitement.…”

Evaluation of a wireless activity monitoring system to quantify locomotor activity in horses in experimental settings

“…For instance, opioids have been reported to increase locomotion and evoke excitation [1]. For instance, opioids have been reported to increase locomotion and evoke excitation [1].…”

Evaluación de protocolos de sedación y analgesia con xilazina y dos tasas de infusión continua de morfina en caballos en estación sometidos a castración vía laparascópica

“…Otros autores han reportado que protocolos de medetomidina y morfina en infusión continua en equinos o xilazina y buprenorfina en bolos IV produjeron disminución de la frecuencia cardíaca y respiratoria (Solano y col 2009, Cruz y col 2011). En general los analgésicos opioides no son depresores cardiovasculares en caballos y tienen mínimos efectos en otras especies; sin embargo algunos efectos tanto estimulantes o depresores cardiovasculares se pueden deber a las dosis altas que causan la excitación o a fenómenos alérgicos que pueden producir efectos depresores (Clutton 2010); en cuanto a las funciones respiratorias los opioides producen depresión de la actividad con aumento de las concentraciones de dióxido de carbono en sangre arterial mediante la activación de receptores y expresados en las neuronas involucradas en el control respiratorio (Dahan y col 2010); sin embargo, la dosificación en infusión continua empleada en este estudio permitió evitar amplias fluctuaciones en las concentraciones plasmáticas y los efectos depresores respiratorios marcados, producidos por la dosificación en bolos que aumentan la presentación de efectos adversos.…”