The analgesic actions of buprenorphine, butorphanol, nalbuphine and pentazocine were assessed in the rabbit by analgesiometry using a thermal stimulus. All four compounds produced effective analgesia without causing serious respiratory depression. Increased dose rates of buprenorphine, butorphanol and nalbuphine produced only a minor increase in the maximum degree of analgesia attained. At the highest dose rates of nalbuphine and butorphanol which were assessed there appeared to be a reduction in the degree of analgesia and its duration of action whereas increased dose rates of buprenorphine produced progressively longer periods of analgesia (0.0075mg/kg - 150min; 0.03mg/kg -660min; 0.3mg/kg - >780 min).
The results indicate that these opioids can be used safely to provide pain relief in rabbits, provided that excessively high dose rates of nalbuphine and butorphanol are avoided.