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

Nicole G. Rolfe Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1H 2W1, Canada.

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Carolyn L. Kerr Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1H 2W1, Canada.

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Wayne N. McDonell Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1H 2W1, Canada.

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DOI:
https://doi.org/10.2460/ajvr.73.5.587
Volume/Issue:
Volume 73: Issue 5
Online Publication Date:
01 May 2012
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Abstract

Objective—To evaluate the cardiopulmonary and sedative effects of the peripheral α2-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 (Pvo2), 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 Pvo2 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 Pvo2 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.

Abstract

Objective—To evaluate the cardiopulmonary and sedative effects of the peripheral α2-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 (Pvo2), 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 Pvo2 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 Pvo2 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.

Contributor Notes

Supported by the Pet-Trust Fund and Merck & Company Incorporated.

The authors thank William Sears for statistical assistance and Gabrielle Monteith for assistance with data analysis.

Address correspondence to Dr. Rolfe (nicolerolfe@yahoo.ca).
Cover American Journal of Veterinary Research
American Journal of Veterinary Research
Publication Date:
01 May 2012
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