Interactions of morphine and isoflurane in horses

Abstract

Our results do not support routine clinical use of MOR administered IV at dosages of 0.25 or 2.0 mg/kg as an adjuvant to anesthesia in horses administered ISO.

Effects of Intravenous Fentanyl Administration on End-Tidal Sevoflurane Concentrations in Thoroughbred Racehorses undergoing Orthopedic Surgery

“…Opioids have been reported to induce central nervous system excitation and subsequent locomotor activity [6]. In another study, the behavioral characteristics of a horse recovering from general anesthesia after administration of a high dose of morphine were clearly not desirable [18]. In the present study, such adverse effects were not observed in Group SF, and the qualities of the recoveries were clinically acceptable.…”

“…A reduction in the minimum alveolar concentration (MAC) of inhalant agents after administration of various drugs is often used as a measure of analgesia in both humans and animals [11,14,18]. In this study, a reduction of about 13% in the sevoflurane requirement was observed in horses administered fentanyl as part of the anesthetic regimen.…”

Cardiopulmonary Effects and Recovery Quality of Remifentanil–Isoflurane Anesthesia in Horses

“…The excitement that occurred in one horse from the remifentanil group was mild, lasted only a short time, and was considered clinically insignificant. In addition, individual animal variability, the potential for opioids cause sympathetic stimulation in horses [13,20], might help explain this finding.…”

“…The MAC reduction in horses after administration of opioids has been disappointing compared with other species. In dogs, 2 mg/kg morphine (IV) resulted in an isoflurane MAC reduction of 50% [25], whereas the same dose in horses resulted in MAC reduction in some horses and an increase in others, along with an undesirable recovery from anesthesia [13]. Alfentanil reduced the MAC of isoflurane in cats [26] but did not alter the MAC of halothane in horses [20].…”

“…Extremely high dosages of m-agonist opioids administered intraoperatively may cause unacceptable excitement in horses during recovery [13], but administration of clinically relevant dosages of m-agonists causes no difference in recovery quality compared with administration of lesser potent opioids [14], and recovery quality is actually better in horses receiving potent m-agonist opioids than those not receiving any opioid [15,16]. Recoveries from remifentanil alone have not been evaluated.…”