Cardiopulmonary and sedative effects of intravenous administration of low doses of medetomidine and xylazine to adult horses

Aloisio C. Bueno From the Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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 DVM, MS
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Janyce Cornick-Seahorn From the Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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 DVM, MS
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Thomas L. Seahorn From the Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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 DVM, MS
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Giselle Hosgood From the Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Rustin M. Moore From the Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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 DVM, PhD

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Abstract

Objective

To determine the cardiopulmonary and sedative effects of medetomidine hydrochloride in adult horses and to compare those effects with effects of an equipotent dose of xylazine hydrochloride.

Animals

10 healthy adult female horses.

Procedure

5 horses were given medetomidine (4 μg/kg of body weight, IV), and the other 5 were given xylazine (0.4 mg/kg, IV). Heart rate, respiratory rate, arterial blood pressures, pulmonary arterial blood pressures, and cardiac output were recorded, and sedation and ataxia scores were assigned before and every 5 minutes after drug administration for 60 minutes. Rectal temperature and blood gas partial pressures were measured every 15 minutes after drug administration.

Results

Arterial blood pressure was significantly decreased throughout the study among horses given medetomidine and was significantly decreased for 40 minutes among horses given xylazine. Compared with baseline values, cardiac output was significantly decreased 10, 20, and 40 minutes after administration of medetomidine and significantly increased 40 and 60 minutes after administration of xylazine. Despite the significant decrease in respiratory rate in both groups, results of blood gas analyses were not significantly changed over time. Ataxia and sedation scores were of similar magnitude for the 2 groups, but ataxia persisted slightly longer among horses given medetomidine. Horses resumed eating hay 10 to 55 minutes after drug administration.

Conclusions and Clinical Relevance

Results suggest that equipotent low doses of medetomidine and xylazine induce comparable levels of ataxia and sedation and similar cardiopulmonary changes in adult horses. (Am J Vet Res 1999;60:1371–1376)

Abstract

Objective

To determine the cardiopulmonary and sedative effects of medetomidine hydrochloride in adult horses and to compare those effects with effects of an equipotent dose of xylazine hydrochloride.

Animals

10 healthy adult female horses.

Procedure

5 horses were given medetomidine (4 μg/kg of body weight, IV), and the other 5 were given xylazine (0.4 mg/kg, IV). Heart rate, respiratory rate, arterial blood pressures, pulmonary arterial blood pressures, and cardiac output were recorded, and sedation and ataxia scores were assigned before and every 5 minutes after drug administration for 60 minutes. Rectal temperature and blood gas partial pressures were measured every 15 minutes after drug administration.

Results

Arterial blood pressure was significantly decreased throughout the study among horses given medetomidine and was significantly decreased for 40 minutes among horses given xylazine. Compared with baseline values, cardiac output was significantly decreased 10, 20, and 40 minutes after administration of medetomidine and significantly increased 40 and 60 minutes after administration of xylazine. Despite the significant decrease in respiratory rate in both groups, results of blood gas analyses were not significantly changed over time. Ataxia and sedation scores were of similar magnitude for the 2 groups, but ataxia persisted slightly longer among horses given medetomidine. Horses resumed eating hay 10 to 55 minutes after drug administration.

Conclusions and Clinical Relevance

Results suggest that equipotent low doses of medetomidine and xylazine induce comparable levels of ataxia and sedation and similar cardiopulmonary changes in adult horses. (Am J Vet Res 1999;60:1371–1376)

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