Comparative Effects of Levomethadone and Butorphanol in Detomidine-Based Premedication Protocols on Sedation and Induction Parameters in Warmblood Horses Undergoing General Anesthesia

Abstract

Background. Opioids are commonly used and combined with α2-agonists in premedication protocols for horses undergoing general anesthesia, to deepen sedation and provide analgesia. Butorphanol is a widely used opioid analgesic in equine practice, although its pharmacological profile may limit its efficacy in longer or more invasive surgical procedures. Levomethadone (Recudon®) is a relatively new opioid drug licensed for horses in the Netherlands. Studies comparing the effects and side effects of both opioids in premedication are currently scarce, and their relative impact on sedation and induction parameters is not yet well established. Study Design. Prospective, randomized, blinded, controlled clinical trial. Aim. To evaluate whether the use of a premedication protocol consisting of detomidine and levomethadone results in significant differences in various sedation and induction parameters compared to a protocol consisting of detomidine and butorphanol. Methods. Twelve healthy adult warmblood horses scheduled for elective surgery were randomized into two premedication protocol groups: LEV (8 μg/kg detomidine + 100 μg/kg levomethadone) or BUT (8 μg/kg detomidine + 20 μg/kg butorphanol). Depth of sedation, degree of ataxia and induction quality were scored using Simple Descriptive Scales, and number of 5 μg/kg detomidine top-ups were recorded. Parameters of both groups were compared using the Mann-Whitney U test. Results. The LEV and BUT group consisted of n=5 and n=7 horses. No significant differences in sedation depth, degree of ataxia or detomidine top-ups were found between groups, but induction quality was significantly lower in the LEV group (p = 0.017). Conclusions. Based on the evaluated parameters, both levomethadone and butorphanol are suitable opioids for combined use with an α2-agonist in premedication of healthy warmblood horses undergoing general anesthesia, although levomethadone was associated with slightly lower, but still clinically acceptable induction quality.