The two drugs are buprenorphine and butorphanol. In the study, researchers tested two different medication protocols, and found that buprenorphine given prior to surgery and during wound closure provided 6 hours of pain control after spay surgery, but cats given butorphanol experienced pain and had to be given rescue analgesia.
Leon N. Warne, DVM; Thierry Beths, DVM, PhD; Merete Holm, DVM; Jennifer E. Carter, DVM; Sébastien H. Bauquier, DVM. Evaluation of the perioperative analgesic efficacy of buprenorphine, compared with butorphanol, in cats. Journal of the American Veterinary Medical Association, July 15, 2014, Vol. 245, No. 2, Pages 195-202. doi: 10.2460/javma.245.2.195