Clinical effects and pharmacokinetics of low-dose butorphanol intravenously in donkeys

Although butorphanol is widely used in equids for sedation, its clinical effects and pharmacokinetics have been poorly investigated in donkeys. This study evaluated the pharmacokinetics of low dose of butorphanol and its effects on heart and respiratory rate, intestinal motility and sedation in donkeys. Eight healthy donkeys aged 2-5 years undergoing non-painful clinical procedures were enrolled. All animals received butorphanol 0.03 mg kg-1 intravenously and blood samples were collected before and 5, 10, 15, 30, 45, 60, 90, 120, 180, 240, 300 and 360 min after administration. At every timepoint, heart and respiratory rate and intestinal sounds were evaluated, and the sedative effect assessed using two composite scales. Plasma butorphanol concentrations were measured using Liquid Chromatography Tandem Mass Spectrometry, and analyzed using Xcalibur 2.0. All plasma concentrations were above the limit of quantification (0.25 ng ml-1), and the mean ± SD of mean residence time, area under the curve, clearance and elimination half-life were 0.88 ± 0.46 h, 52.1 ± 17.0 h mcg L-1, 0.64 ± 0.22 L h-1 Kg-1, 2.10 ± 0.52 h, respectively. Level of sedation was mild 15 min after drug administration and absent at 45 min; no other statistically significant changes were observed in the physiologic parameters. This study suggests that low dose of butorphanol in donkeys may provide mild short-term sedation without affecting heart and respiratory rate or enteric motility. Pharmacokinetics parameters support clinical observations, as more than 60% of the dose was removed from plasma 53 min after injection.