Methadone-fluconazole formulations provide superior clinical efficacy compared to buprenorphine injection in dogs undergoing soft tissue surgery.

OBJECTIVE

To determine the perioperative efficacy and safety of methadone-fluconazole injection followed by oral methadone-fluconazole-naltrexone (methadone-fluconazole) compared to IM buprenorphine followed by oral codeine (buprenorphine).

METHODS

Healthy dogs undergoing elective ovariohysterectomy or castration from October 2019 through December 2019 were blocked to treatment by week. The methadone-fluconazole group treatment included methadone-fluconazole (0.5 and 2.5 mg/kg, SC) preoperatively and once postoperatively; methadone-fluconazole-naltrexone (0.5, 2.5, and 0.125 mg/kg, PO, q 12 h) and an NSAID started approximately 24 hours after surgery. The buprenorphine group included buprenorphine preoperatively (0.02 mg/kg, IM) and postoperatively (0.01 mg/kg, IM), and then codeine (1 to 2 mg/kg, PO, q 8 h) and an NSAID started approximately 8 hours postoperatively. Preoperative sedation included acepromazine; anesthetic induction included ketamine-midazolam and isoflurane anesthesia. Faculty-supervised veterinary students performed the anesthesia and surgery. The Glasgow Composite Measure Pain Scale assessed postoperative pain; treatment failures included total pain scores > 5 (if nonmobile), > 6 (if mobile), and need for additional analgesia/sedation. Variables of interest were compared between groups.

RESULTS

Enrollment included 119 dogs in the methadone-fluconaze group (47 male, 72 female) and 120 dogs in the buprenorphine group (44 male, 76 female). One dog was excluded (methadone-fluconazole) due to requiring additional surgery. Propofol was needed for anesthetic induction in 2 methadone-fluconazole and 8 buprenorphine dogs. Ephedrine was administered for intraoperative hypotension to 4 of 119 (methadone-fluconazole) and 8 of 120 (buprenorphine) dogs. One dog (methadone) received atropine. Mean ± SD postoperative rectal temperatures were significantly lower in methadone-fluconazole (35.6 ± 1.1 °C) than buprenorphine (36.1 ± 1.0 °C) dogs. Significantly more treatment failures occurred from buprenorphine (8 of 120) than methadone-fluconazole (1 of 119).

CONCLUSIONS

Methadone-fluconazole formulations provided superior clinical efficacy compared to buprenorphine.

CLINICAL RELEVANCE: Methadone-fluconazole formulations provide effective analgesia with twice-daily administration.