The cardiopulmonary effects of a peripheral alpha-2-adrenoceptor antagonist, MK-467, in dogs sedated with a combination of medetomidine and butorphanol.

OBJECTIVE: To compare the cardiopulmonary effects of intravenous (IV) and intramuscular (IM) medetomidine and butorphanol with or without MK-467.

STUDY DESIGN: Prospective, randomized experimental cross-over.

ANIMALS: Eight purpose-bred beagles (two females, six males), 3-4 years old and weighing 14.5 ±1.6 kg (mean ± SD).

METHODS: All dogs received four different treatments as follows: medetomidine 20 μg kg(-1) and butorphanol tartrate 0.1 mg kg(-1) IV and IM (MB), and MB combined with MK-467,500 μg kg(-1) (MBMK) IV and IM. Heart rate (HR), arterial blood pressures (SAP, MAP, DAP), central venous pressure (CVP), cardiac output, respiratory rate (fR ), rectal temperature (RT) were measured and arterial blood samples were obtained for gas analysis at baseline and at 3, 10, 20, 30, 45 and 60 minutes after drug administration. The cardiac index (CI), systemic vascular resistance index (SVRI) and oxygen delivery index (DO2 I) were calculated. After the follow-up period atipamezole 50 μg kg(-1) IM was given to reverse sedation.

RESULTS: HR, CI and DO2 I were significantly higher with MBMK after both IV and IM administration. Similarly, SAP, MAP, DAP, CVP, SVRI and RT were significantly lower after MBMK than with MB. There were no differences in fR between treatments, but arterial partial pressure of oxygen decreased transiently after all treatments. Recoveries were uneventful following atipamezole administration after all treatments.

CONCLUSIONS AND CLINICAL RELEVANCE: MK-467 attenuated the cardiovascular effects of a medetomidine-butorphanol combination after IV and IM administration.