Changes in the thermal threshold response in eight cats after administration of buphrenorphine, butorphanol and morphine

Comparison of three different opoid pain relievers in cats

source: S.A. Robertson et al
Veterinary Record vol 153, no 15, October 11 2003
starts p462, 4 pages long

There is not enough information on the best way to relieve pain in cats, though they are the most numerous pets, both in the UK and US, and are likely to be operated on at least once in their lives, since most are neutered. Doses are often based on data for other species, and cats may not be given any painkillers at all after surgery or accidents, due to fears of an adverse reaction. This study examines the thermal threshold in cats, as a way of assessing acute pain. The study assesses how long the painkiller takes to become effective, how effective it is, and how long it lasts for. The three painkillers assessed are: morphine, buphrenorphine, and butorphanol. Eight cats took part in the study, five neutered females, two entire females, and one neutered male. The cats were subject to a mild heat stimulus, and the cats' reactions were assessed. All the cats involved were tested using a saline placebo, and with at least two of the painkillers.

All three painkillers proved to be effective, though the timing of their effects varied. Butorphanol took effect after five minutes, but lasted less time than either morphine or bupreorphine. Morphine was effective from four to six hours following the injection, and buprenorphine had an effect between four hours and twelve hours following the injection. The cats also showed signs of euphoria, lasting under half an hour with butorphanol, between two and three hours with morphine, and for as long as 24 hours for some cats given buprenorphine. The cats given morphine all vomited after their injections.
Butorphanol appears to be a poor postoperative painkiller for cats, while buprenorphine apparently lasts longer than morphine, a result backed by a previous study as well as this research. Pethidine has also been tested, and found to be effective for longer than butorphanol, but less time than either morphine or buprenorphine. There is a need for further research, though it is heartening that buprenorphine is commonly used to deal with postoperative pain in cats.