Evaluation of the analgesic properties of acepromazine maleate, oxymorphone, medetomidine and a combination of acepromazine-oxymorphone.

Objective: To determine the presence and duration of analgesia after oxymorphone, acepromazine maleate, acepromazine-oxymorphone combination and medetomidine administration in dogs.

Study Design: Blinded, controlled study.

Animals: Six adult beagle dogs.

Methods: Each dog participated in five trials receiving acepromazine maleate (0.2 mg kg IM), oxymorphone (0.2 mg kg IM), acepromazine-oxymorphone drug combination (0.2 mg kg each IM), medetomidine (20 μg kg IM) and sterile saline (control). Two specially designed instruments were used for analgesia determination: a heat device (HD) utilized a linear ramped intensity incandescent bulb and a pressure device (PD) consisted of a pneumatic cylinder that protruded a 2.5-cm bolt. The minimum pressure and heat necessary to produce an avoidance response were determined. Analgesia testing was performed prior to and at 30-minute intervals for six hours after drug administration.

Results: Oxymorphone, acepromazine-oxymorphone and medetomidine significantly elevated both pressure and heat response thresholds compared to controls and acepromazine. Both medetomidine and acepromazine-oxymorphone provided a significantly longer duration of analgesia than oxymorphone. No adverse effects were observed at any of the thermal or pressure application sites.

Conclusions: Oxymorphone, medetomidine and acepromazine-oxymorphone produced significant analgesia with medetomidine and acepromazine-oxymorphone providing the longest duration of analgesia.