The analgesic effects of intrathecal xylazine and detomidine in sheep and their antagonism with systemic atipamezole

Abstract

ObjectiveTo evaluate the analgesic and adverse side effects of intrathecal (IT) xylazine (XYL) and detomidine (DET) and the subsequent effects of two doses of intravenous (IV) atipamezole (ATI). Study designProspective, randomized, cross-over. AnimalsFive adult healthy female sheep with mean body mass of 55 ± 2.3 kg. Material and methodsEach sheep underwent four treatments: 1) 50 μg kg−1 XYL IT and 5 μg kg−1 ATI IV, 2) 50 μg kg−1 XYL IT and 2.5 μg kg−1 ATI IV, 3) 10 μg kg−1 DET IT and 5 μg kg−1 ATI IV, 4) 10 μg kg−1 DET IT and 2.5 μg kg−1 ATI IV. Pain threshold (TH) was tested by applying pulsed and stepwise incremental direct current to the skin overlying the pastern. The current at the point of foot lift was recorded as the TH. Heart rate (HR), mean arterial pressure, arterial oxygen (PO2) and carbon dioxide (PCO2) tensions were monitored. Outcomes were derived as differences between baseline assessment and measurements after treatment. Two-way anova was used to analyse drug effects, treatment differences between groups were examined with an F-test or Wilcoxon's rank sum test in case of non-parametric data distribution. p was set at 0.05. ResultsBoth drugs increased the pain TH, caused small increases in PCO2, and small decreases in HR, the latter was only significant for XYL recipients. Xylazine produced a significantly higher TH, more rapidly and for longer than DET. Atipamezole only significantly affected PaCO2 in the XYL group 2. The pain TH was not affected in either group after IV ATI. ConclusionsAt the doses used, IT XYL, and to a lesser extent DET, induced pastern analgesia. Atipamezole 5 μg kg−1 IV antagonized some side effects without affecting analgesia. Clinical relevanceIntrathecal XYL may be useful as an analgesic in sheep. Its safety is increased because IV ATI antagonizes side effects, but not analgesia.