Buprenorphine Versus Methadone in Female New Zealand White Rabbits Undergoing Balanced Anaesthesia for Calvaria Surgery

Buprenorphine has gained widespread popularity for use in rabbits, while much less is known about methadone. Our aim was to compare sedative, analgesic, and respiratory effects of methadone and buprenorphine as part of balanced anaesthesia. Forty-eight female New Zealand white rabbits undergoing calvaria defects were randomly equally assigned to receive either 0.03 mg kg^-1 of buprenorphine (group B) or 0.3 mg kg^-1 of methadone (group M) in combination with 15 mg kg^-1 of ketamine and 0.1 mg kg^-1 of dexmedetomidine SC. Fifteen minutes later, sedation was scored. A laryngeal mask was placed, and inhalational anaesthesia started. Rescue intraoperative analgesia was administered based on autonomic variations. Arterial blood gases were analysed intra- and postoperatively. Postoperative analgesia was administered if the Rabbit Grimace Scale (RbtGS) score was ≥4. The Mann-Whitney test, <i>t</i>-test, and relative risk followed by chi-square test were used to compare the treatment groups. Deeper sedation was observed in rabbits of group M than in those of group B. Rescue analgesia was administered intraoperatively to seven animals in group B and five in group M (<i>p</i> = 0.739) and postoperatively to three in group B and twelve in group M (<i>p</i> = 0.013). Rabbits of both groups showed short-term respiratory acidosis. RbtGS scores indicated better and longer analgesia in group B compared to group M.