Antagonistic effect of atipamezole on xylazine-induced sedation, bradycardia, and ruminal atony in calves

James R. Thompson From the Departments of Veterinary Clinical Sciences (Thompson, Kersting), and Veterinary Physiology and Pharmacology (Hsu), Iowa State University, Arnes, IA 50011.

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Karl W. Kersting From the Departments of Veterinary Clinical Sciences (Thompson, Kersting), and Veterinary Physiology and Pharmacology (Hsu), Iowa State University, Arnes, IA 50011.

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Walter H. Hsu From the Departments of Veterinary Clinical Sciences (Thompson, Kersting), and Veterinary Physiology and Pharmacology (Hsu), Iowa State University, Arnes, IA 50011.

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Summary

Three doses of an α2-adrenoreceptor antagonist, atipamezole, were administered to reverse xylazine-induced sedation, bradycardia, and ruminal atony in calves. Once a week for 4 weeks, each of 6 calves was administered iv 1 treatment of: 0.3 mg of xylazine/kg of body weight, followed in 10 minutes by 1 ml of 0.9% NaCl; 0.3 mg of xylazine/kg, followed in 10 minutes by 3 μg of atipamezole/kg; 0.3 mg of xylazine/kg, followed in 10 minutes by 10 μg of atipamezole/kg; or 0.3 mg of xylazine/kg, followed in 10 minutes by 30 μg of atipamezole/kg. The order of the 4 treatments in each calf was selected at random. Xylazine alone caused lateral recumbency for 33.6 ±7.1 minutes (mean ± sem-). Atipamezole administered at dosages of 3, 10, and 30 μg/kg shortened xylazine-induced lateral recumbency to 20.5 ± 3.0, 10.2 ± 0.2, and 9.3 ± 0.5 minutes, respectively. Calves given xylazine alone stood at > 60 minutes after the onset of recumbency. Atipamezole given at 3, 10, and 30 μg/kg shortened the time from onset of lateral recumbency to standing to 40.2 ± 6.9, 12.8 ± 1.1, and 10.0 ± 0.7 minutes, respectively. Drowsiness was found in calves given the lowest dosage of atipamezole (3 μg/kg) after the calves stood.

Atipamezole given at dosages of 10 and 30 μg/kg reversed xylazine-induced ruminal atony in a dose-dependent manner. In addition, 30 μg of atipamezole/kg reversed xylazine-induced bradycardia, but the lower dosages of this antagonist did not. Results indicated that 30 μg of atipamezole/kg should be a useful antidote for xylazine overdose in cattle.

Summary

Three doses of an α2-adrenoreceptor antagonist, atipamezole, were administered to reverse xylazine-induced sedation, bradycardia, and ruminal atony in calves. Once a week for 4 weeks, each of 6 calves was administered iv 1 treatment of: 0.3 mg of xylazine/kg of body weight, followed in 10 minutes by 1 ml of 0.9% NaCl; 0.3 mg of xylazine/kg, followed in 10 minutes by 3 μg of atipamezole/kg; 0.3 mg of xylazine/kg, followed in 10 minutes by 10 μg of atipamezole/kg; or 0.3 mg of xylazine/kg, followed in 10 minutes by 30 μg of atipamezole/kg. The order of the 4 treatments in each calf was selected at random. Xylazine alone caused lateral recumbency for 33.6 ±7.1 minutes (mean ± sem-). Atipamezole administered at dosages of 3, 10, and 30 μg/kg shortened xylazine-induced lateral recumbency to 20.5 ± 3.0, 10.2 ± 0.2, and 9.3 ± 0.5 minutes, respectively. Calves given xylazine alone stood at > 60 minutes after the onset of recumbency. Atipamezole given at 3, 10, and 30 μg/kg shortened the time from onset of lateral recumbency to standing to 40.2 ± 6.9, 12.8 ± 1.1, and 10.0 ± 0.7 minutes, respectively. Drowsiness was found in calves given the lowest dosage of atipamezole (3 μg/kg) after the calves stood.

Atipamezole given at dosages of 10 and 30 μg/kg reversed xylazine-induced ruminal atony in a dose-dependent manner. In addition, 30 μg of atipamezole/kg reversed xylazine-induced bradycardia, but the lower dosages of this antagonist did not. Results indicated that 30 μg of atipamezole/kg should be a useful antidote for xylazine overdose in cattle.

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