Analgesic effect of butorphanol and levomethadone in detomidine sedated horses

The analgesic potency of butorphanol 25 mug/kg bodyweight (BW) and levomethadone 100 mug/kg BW, administered together with detomidine 10 mug/kg BW, was measured in twelve Warmblood horses in a randomized, blinded cross-over study. Detomidine with saline 10 ml 0.9 % was used as placebo. The nociceptive threshold was determined using a constant current and a pneumatic pressure model for somatic pain. Detomidine alone and in combination with butorphanol or levomethadone caused a significant temporary increase (P < 0.05) of the nociceptive threshold with a maximum effect within 15 min and a return to baseline levels within 90 min. Butorphanol and levomethadone increased the nociceptive threshold and prolonged the duration of anti-nociception significantly from 15 to 75 min (P < 0.05) after drug administration compared with detomidine alone to both test methods. No significant difference between butorphanol and levomethadone was registered. It is concluded that the addition of butorphanol or levomethadone to detomidine increases the nociceptive threshold to somatic pain and prolongs the analgesic effect of detomidine in the horse.