Bioavailability of butorphanol after intranasal administration to horses

Abstract

The aim of the present study was to describe butorphanol pharmacokinetics and bioavailability following intranasal administration to horses. Six adult horses received 0.05 mg/kg butorphanol, in a randomised crossover design, by either intravenous or intranasal route. Plasma concentrations of bu-torphanol were measured at predetermined time points using liquid chromatography/mass spectrome-try assay. After intravenous injection, mean ±SD butorphanol steady-state volume of distribution and clearance was 3.20 ± 1.77 L/kg and 3.18 ± 1.47 L/kg/h, respectively. Terminal half-lives for butor-phanol after intravenous and intranasal administrations were 0.68 ± 0.17 h and 1.79 ± 1.43 h. For intranasal administration, absorption half-life and peak plasma concentration were 0.43 ± 0.33 h and 1.95 ± 1.7 ng/mL, respectively. Bioavailability was 54.45 ± 20.09%. Intranasal butorphanol administration in horses is practical, not stressful and well tolerated. Therefore, it might be a substitute to the intravenous route in adult horses.