Methadone or Butorphanol as Pre-Anaesthetic Agents Combined with Romifidine in Horses Undergoing Elective Surgery: Qualitative Assessment of Sedation and Induction

Abstract

While butorphanol is the most commonly used opioid in horses, methadone is not licensed in most countries. Our aim was to compare the effects of both drugs, combined with romifidine, regarding the quality of sedation and induction in horses undergoing elective surgery. Results indicate the suitability of both methadone and butorphanol in this patient population. Animals were scored 10 min after intravenous injection of sedatives. Despite lower overall sedation (OS) score in horses receiving methadone (p = 0.002), the quality and time of induction and intubation remained unchanged. None of the horses had the lowest OS score (no sedation), nor the highest score for ataxia (horse falling). Methadone induced a tendency for minor noise reaction yet minor head lowering scores, the latter being probably the most influencing parameter when scoring OS. Measured physiological parameters decreased in both groups, with greater bradycardia recorded after methadone (p = 0.017), including a higher incidence of atrioventricular blocks that resolved during general anaesthesia. The quality of induction was good–excellent in most of the animals. While comparisons between the degree of antinociception were beyond the scope of this study, analgesic potency might influence the choice when considering opioids as pre-anaesthetic drugs in combination with romifidine before surgery in equines.

Opioid‐free anaesthesia protocol for standing spinal surgery in a horse

“…In one study in healthy horses undergoing elective surgery, methadone was shown to enhance sedation from alpha‐2 adrenoceptor agonists. It has also been shown to decrease noise response while maintaining good postural stability 21 . However, the analgesic effects of methadone and its duration remain to be investigated in the equine population.…”

“…It has also been shown to decrease noise response while maintaining good postu-ral stability. 21 However, the analgesic effects of methadone and its duration remain to be investigated in the equine population.…”

Opioid‐free sedation for atlantoaxial cerebrospinal fluid collection in adult horses

“…24 While well-suited for assessing sedation depth in standing, undisturbed horses, these methods are not easily applied to sedated horses undergoing a potentially painful stimulus. Scoring systems have been described for assessing horse responses to various tactile, auditory, and visual stimuli 2,22,25,26 ; however, reviewerassigned scoring systems are inherently prone to subjectivity and scorer bias. Alternatively, automated analysis of animal behavior is widely utilized in biomedical research, and open-source availability of software code enables modification to perform the specific needs of a particular study.…”