Effectiveness of tolazoline in reversing xylazine-induced sedation in calves

Abstract

Objective - To test effectiveness of IV administration of tolazoline hydrochloride in reversing xylazine hydrochloride-induced sedation in calves. Design - Prospective study. Animals - 12 female and 12 male Friesian-cross calves from 5 to 7 months old. Procedure - Calves were assigned to 1 to 4 treatment groups. Calves were given xylazine (0.3 mg/kg [0.14 mg/lb] of body weight, IM). Twenty minutes later, calves were treated with saline (0.9% NaCl) solution (1 ml/50 kg [1 ml/110 lb], IV) or tolazoline (1, 2, or 4 mg/kg [0.45, 0.9, or 1.8 mg/lb], IV). Behavioral and physiological measurements included elapsed time form xylazine administration to recumbency, arousal and standing times after reversal drug administration, heart rate, and respiratory rate. Results - Mean (± SD) recumbency time for all calves was 5.4 ± 1.8 minutes. Compared with administration of saline solution, all 3 doses of tolazoline significantly decreased arousal and standing times. Mean arousal time for calves receiving saline solution was 27.8 ± 11.5 minutes. Administration of tolazoline at 1, 2, and 4 mg/kg resulted in mean arousal times of 4.7 ± 3.8, 0.9 ± 0.5, and 0.7 ± 0.3 minutes, respectively. Mean standing time for calves receiving saline solution was 38.8 ± 2.8 minutes. Administration of tolazoline at 1, 2, and 4 mg/kg resulted in mean standing times of 14.0 ± 11.0, 3.0 ± 1.2, and 2.4 ± 1.1 minutes, respectively. Clinical Implications - For routine use, tolazoline doses of 1 to 2 mg/kg should suffice. In cattle, IV administration of tolazoline reverses pharmacologic effects of xylazine, thereby hastening recovery from xylazine- induced sedation.