Exposure to Subcutaneously Administered Butorphanol in Horses Pre-Treated With Detomidine or Detomidine-Vatinoxan

The aim of the study was to determine the exposure to subcutaneously administered butorphanol in horses pre-treated with intravenous (IV) detomidine, with or without vatinoxan, a peripherally selective alpha₂-adrenoceptor antagonist. Five healthy, adult horses received three IV treatments 7 days apart, in a randomized, cross-over design: detomidine 20 μg/kg (DET-B), detomidine 20 μg/kg with vatinoxan 200 μg/kg (DETVAT-B) and saline (S-B), all followed by 0.1 mg/kg of butorphanol administered subcutaneously 30 min later. Venous samples were collected between 10 and 270 min after butorphanol administration. Butorphanol concentrations in plasma were analyzed with liquid chromatography coupled with triple quadruple mass spectrometry. Data were analyzed with non-compartmental methods. The observed areas under plasma butorphanol concentration-time curves were 8104 ± 2590, 7042 ± 2628 and 5996 ± 1670 ng·min/mL for DET-B, DETVAT-B and S-B, respectively. There were no significant differences between treatments. Pre-treatment with detomidine, with or without vatinoxan, did not significantly affect the exposure to subcutaneously administered butorphanol in this study.