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Comparing common preoperative analgesics

Warne LN, Beths T, Holm M, et al.  Evaluation of the perioperative analgesic efficacy of buprenorphine, compared with butorphanol, in cats.  Journal of the American Veterinary Medical Association 2014;245:195-202.

Both butorphanol and buprenorphine are common injectable opioid analgesics used in cats.  In this 2-phase positve-controlled randomized masked clinical trial, 39 healthy female cats underwent routine ovariohysterectomy and were given either butorphanol or buprenorphine for analgesia.  All cats received the same anesthesia protocol and were operated on by the same surgeon using the same surgical technique (midline approach).  The same veterinary anesthesiologist, who was unaware of the treatments each cat received, performed all pre- and postoperative pain assessments using a published multidimensional composite pain scoring system validated for evaluating postoperative pain in ovariohysterectomized cats.  Pain scoring was performed beginning 20 minutes after extubation and continuing up to 360 minutes post-extubation.

In phase 1 of the study, 4 cats received buprenorphine, 0.02 mg/kg intramuscularly (IM) and 6 cats received butorphanol, 0.4 mg/kg IM preoperatively In phase 1, 9 of the 10 subjects required rescue analgesia (methadone and meloxicam), and due to the high requirement for rescue analgesia in this group, phase 1 was discontinued for ethical reasons.  In phase 2 of the study, the same experimental design was followed and 29 cats, 14 in the buprenorphine group and 15 in the butorphanol group, received the same doses of their assigned pre-operative opioid as the phase 1 cats, but these patients also received an additional dose of the same opioid at the same dosage as pre-operatively during wound closure.  All cats from the phase 2 butorphanol group required rescue analgesia at 20 minutes postoperatively and were not evaluated at further time points.  None of the cats in the phase 2 buprenorphine group required rescue analgesia and their pain scores declined at time points past 20 minutes postoperatively.

It is not surprising that buprenorphine would provide superior analgesia in these patients, as it is a partial m-opioid receptor agonist (and k-opioid receptor antagonist), while butorphanol is a m-opioid receptor antagonist (and k-opioid receptor agonist).  In order to achive adequate analgesia for at least 6 hours postoperatively in these patients, buprenorphine at 0.02 mg/kg IM had to be given twice, once preoperatively and once during wound closure, but these researchers state that it is possible that a single dose of 0.04 mg/kg IM might also provide equally sufficient analgesia.  Butorphanol did not provide adequate analgesia in patients in either phase of the trial.  [PJS]

See also:
Brondani JT, Luna SP, Padovani CR. Refinement and initial validation of a multidimensionsal composite scale for use in assessing acute postoperative pain in cats. Am J Vet Res; 2011 Feb 72 (2):174-83.