ANTINOCICEPTIVE EFFECTS OF OXYMORPHONE-BUTORPHANOL-ACEPROMAZINE COMBINATION IN CATS

Objective-To determine the antinociceptive effects of oxymorphone, but orphanol, and acepromazine individually and in combination to a noxiou s visceral stimulus in cats. Study Design-Randomized, blinded controll ed study. Animals-Eight healthy mixed-breed cats (four male, four fema le) weighing 4.4 +/- 1.2 kg and aged 1 to 2 years old. Methods-A silas tic balloon catheter was inserted per rectum and inflated at various p ressures. Physiological parameters (respiratory rate, pulse rate, and blood pressure) were also recorded. Subjects were administered individ ual and combined intravenous (IV) doses of 0.025, 0.05, 0.10, and 0.20 mg/kg oxymorphone and 0.025, 0.05, 0.10, and 0.20 mg/kg butorphanol. A further study of Various ratios of butorphanol and oxymorphone (3:1, 2:1, 1:1, 1:2, and 1:3). at a combined equivalent dose of 0.1 mg/kg, was performed in four cats per dose combination. Tn a separate study, four cats were administered combined IV doses of 0.05 mg/kg each of ox ymorphone and butorphanol or 0.05 mg/kg each of oxymorphone, butorphan ol, and acepromazine. Results-Combined doses of 0.05 and 0.10 mg/kg of oxymorphone and butorphanol showed mainly additive with some synergis tic antinociceptive interactions and the combined dose of 0.2 mg/kg of each agent demonstrated additional antinociceptive effects, P < .05. Additional studies showed that various ratios of the two agents at a t otal combined dose of 0.10 mg/kg IV did not produce levels of antinoci ception that were significantly different from each other, P > .05. Ac epromazine (ACE) significantly increased the magnitude of antinocicept ion at 15 minutes when administered in combination with oxymorphone an d butorphanol, P < .05. Also, physiological variables were unaffected by these drug combinations. Conclusions-Low doses of oxymorphone and b utorphanol in combination can produce greater levels of antinociceptio n than when used individually. ACE, in conjunction with oxymorphone an d butorphanol, produced even greater levels of antinociception than th e two-opioid drug combination. Clinical Relevance-Oxymorphone, butorph anol, and ACE can be used in combination to produce additive or synerg istic effects without adverse effects in cats. These data suggest that ACE and butorphanol at low doses given as preanesthetic medication fo llowed by a mu opioid (eg, oxymorphone) after surgery at low doses may provide an effective method of pain management in the cat. (C) Copyri ght 1998 by the American College of Veterinary Surgeons.