Methadone Versus Buprenorphine for Ovariohysterectomy Analgesia in Cats

In the Literature

Shah M, Yates D, Hunt J, Murrell J. Comparison between methadone and buprenorphine within the QUAD protocol for perioperative analgesia in cats undergoing ovariohysterectomy. J Feline Med Surg. 2019;21(8):723-731.

The Research …

Methadone, a full opioid μ-receptor agonist, is expected to provide more profound analgesia as compared with buprenorphine, a partial opioid μ-receptor agonist.¹ However, this has been difficult to prove, especially in cats, a species known to hide pain.²

In this clinical study* of cats undergoing ovariohysterectomy (OHE), the authors used a multimodal protocol of buprenorphine with medetomidine, ketamine, and diazepam combined and administered IM (ie, QUAD protocol) or the same protocol using methadone instead of buprenorphine. Administration of meloxicam was reserved until after completion of surgery and pain assessments. Sixty cats were included in each group, and multiple methods were used to assess both pain and sedation.

Cats receiving methadone were found to have lower pain scores than cats receiving buprenorphine, with a greater percentage of cats in the buprenorphine group requiring rescue analgesia. This difference in pain scores was identified with one pain scoring system (ie, the Glasgow Composite Measure Pain Scale) but not with pain assessments using the dynamic interactive visual analogue scale and mechanical nociceptive threshold testing. Hyperalgesia, as measured by mechanical nociceptive threshold testing, developed in every cat; this is a common sequela of tissue injury and is mediated, in large part, by inflammation.

… The Takeaways

Key pearls to put into practice:

• Although commonly referred to as a routine surgery, OHE is not routine for the patient and can be painful.

• In this study, despite a robust multimodal analgesia protocol, a significant number of cats needed rescue analgesia in recovery. A validated pain scoring system should be used to assess the pain level of all postsurgical patients, including those undergoing OHE.

• The Glasgow Composite Measure Pain Scale is validated to indicate pain in cats, allows for reduced assessor variability by using defined behaviors weighted by severity, and provides intervention guidelines (see Suggested Reading).^3,4 The scale is easy to implement and should be strongly considered as an essential tool for pain assessment in cats.

• Methadone is a more potent analgesic for OHE pain than buprenorphine. Although methadone is expensive in the United States, feline doses are unlikely to be cost-prohibitive, and the investment preoperatively may help decrease costs by decreasing the need for rescue analgesia and further drug administrations.

• Although hyperalgesia occurred in this study despite a robust protocol, administration of NSAIDs early in the pain process as appropriate for the patient may help decrease the occurrence of hyperalgesia.

*Study funded by Dechra Animal Health