Atipamezole changes the antinociceptive effects of butorphanol after medetomidine-ketamine anaesthesia in rats

Objective To investigate the effects of atipamezole administered before butorphanol, on tail-flick latency (TFL) and also following medetomidine-ketamine anaesthesia in rats. Study design Prospective, randomized experimental study. Animals Thirty-four adult male Sprague-Dawley rats weighing 260-390 g. Methods TFL in 50 degrees C water was used to measure antinociception. In the first experiment, rats received saline (n = 5) or atipamezole (n = 5) followed by butorphanol treatments. In the second experiment, three groups of rats received saline (n = 8), atipamezole (n = 8) or atimpamezole (n = 8) followed by butorphanol 60 minutes after medetomidine-ketamine administration. Results In the first experiment, butorphanol significantly increased TFL compared to baseline. Atipamezole significantly decreased this effect. In the second experiment, TFL was significantly increased after recovery from medetomidine-ketamine anaesthesia compared to baseline. This was almost completely blocked by atipamezole. Atipamezole with butorphanol after recovery from the anaesthesia significantly reduced TFL compared to saline but still significantly increased TFL compared to the baseline. Conclusion and clinical relevance Atipamezole attenuated the analgesic effects of butorphanol. When postoperative atipamezole is used to hasten recovery from anaesthesia in rats, it may interfere with the postoperative analgesic effect of butorphanol.