Cardiopulmonary and sedative effects of the peripheral α2-adrenoceptor antagonist MK 0467 administered intravenously or intramuscularly concurrently with medetomidine in dogs.

OBJECTIVE

To evaluate the cardiopulmonary and sedative effects of the peripheral α(2)-adrenoceptor antagonist MK 0467 when administered IM or IV concurrently with medetomidine in dogs.

ANIMALS: 8 adult dogs.

PROCEDURES: Dogs received 20 μg of medetomidine/kg, IM, alone or concurrently with MK 0467 (0.4 mg/kg, IM), and 10 μg of medetomidine/kg, IV, alone or concurrently with MK 0467 (0.2 mg/kg, IV), in a randomized crossover study. Sedation characteristics were scored and hemodynamic measurements and arterial and mixed-venous blood samples for blood gas analysis were obtained before (time 0; baseline) and for 90 minutes after treatment.

RESULTS

Heart rate (HR), mixed-venous partial pressure of oxygen (Pvo(2)), and cardiac index (CI) were significantly lower and mean arterial blood pressure (MAP), systemic vascular resistance (SVR), and oxygen extraction ratio (ER) were significantly higher after administration of medetomidine IM or IV, compared with baseline values. Administration of medetomidine and MK 0467 IM caused a significantly higher heart rate, CI, and Pvo(2) and significantly lower MAP, SVR, and ER for 60 to 90 minutes than did IM administration of medetomidine alone. Administration of medetomidine and MK 0467 IV caused a significantly higher CI and Pvo(2) and significantly lower MAP, SVR, and ER for 45 to 90 minutes than did IV administration of medetomidine alone. There was no significant difference in sedation scores among treatments.

CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, MK 0467 administered concurrently with medetomidine IV or IM reduced the cardiovascular effects of medetomidine but had no detectable effect on sedation scores.