Comparison of the analgesic effects of xylazine in sheep via three different administration routes.
OBJECTIVE
To examine the influence of administration route on the analgesic effects of identical doses of xylazine in sheep. A prospective, linear, randomised laboratory study.


METHODS
The analgesic response to the administration of 2.5 mg of the alpha2 agonist xylazine either intravenously, intramuscularly or subcutaneously was assessed using an analgesia testing method based upon a learned response to a painful electrical stimulus.


RESULTS
Intravenous administration achieved the most rapid onset and highest peak analgesic values of all administration methods, but was characterised by a shorter duration of action (25 min). Intramuscular and subcutaneous administration resulted in a longer duration of action (40 min) and a greater total analgesic response.


CONCLUSIONS
For the routine management of acute pain, intramuscular administration provided the best combination of onset, duration and total analgesic response of the routes examined. The absence of adverse side effects, such as sedation, normally associated with the administration of alpha2 agonists should also encourage the use of this method as a simple and effective means of providing significant analgesia in the sheep.
Grant
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Department of Anaesthesia and Intensive Care, University of Adelaide, South Australia 5005.
Upton
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RN
D000316:Adrenergic alpha-Agonists / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*; D000818:Animals; D019540:Area Under Curve; D007273:Injections, Intramuscular / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D007279:Injections, Subcutaneous / Q000662:veterinary; D010147:Pain Measurement / Q000187:drug effects / Q000662:veterinary; D011446:Prospective Studies; D012756:Sheep / Q000378:metabolism*; D014991:Xylazine / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D014991:Xylazine