Methadone or buprenorphine: which is the better analgesic for feline ovariohysterectomy?

PICO question: In female cats undergoing routine ovariohysterectomy, is using methadone, compared to buprenorphine, in the anaesthetic protocol associated with lower postoperative pain scores? Clinical bottom line: Category of research: Treatment. Number and type of study designs reviewed: Four assessor-blinded randomised controlled trials. Strength of evidence: Moderate. Outcomes reported: Two studies found methadone to be associated with significantly lower postoperative pain scores than buprenorphine; one showed significantly different pain scores over the entire 8-hour postoperative period and one only at 10 minutes postextubation. One study found buprenorphine to be associated with lower postoperative pain scores at some time points postsurgery. One study found no significant difference in pain scores between methadone and buprenorphine. Conclusion: It can be concluded that using methadone in the anaesthetic protocol may provide better analgesia for cats undergoing ovariohysterectomy compared to buprenorphine. The two papers that used validated pain scoring both concluded that methadone was associated with lower pain scores at some points postoperatively. Although one of the studies concluded that buprenorphine is associated with lower postoperative pain scores, this paper provides only very weak evidence because an unvalidated pain scoring method was used. More evidence is needed to confidently recommend using one opioid over another.