Plasma concentrations of Tapentadol and clinical evaluations of a combination of Tapentadol plus Sevoflurane for surgical anaesthesia and analgesia in rabbits (Oryctolagus cuniculus) undergoing orchiectomy

Pain is probably under-treated in animals, particularly in rabbits, due to a lack of familiarity with the species and limited information about analgesic dose, efficacy and safety. Tapentadol (TAP) is a novel opioid drug, with a proven efficacy and safety profile in humans, which could be useful as an analgesic in rabbits. In a clinical study, TAP was administered (5 mg/kg, IV) to seven male New Zealand White rabbits 5 min before anaesthetic induction with sevoflurane to perform orchiectomy. Monitoring of vital signs, including heart rate, electrocardiogram, respiratory rate, invasive blood pressure, oxygen saturation, righting reflex, palpebral reflex, jaw tone and tongue retraction, was performed throughout surgery. Pain was assessed for 8 h following surgery, using previously validated parameters, physiological assessments and behavioural assessments. Blood was also collected at regular intervals to assess the pharmacokinetic profile of the drug. TAP was rapidly distributed and eliminated in rabbits. Apnoea did not occurred in any subject. Following surgery, there were very few observable signs of pain in four rabbits and all resumed normal activities within a few hours. In conclusion, this is the first study about the clinical effects and potential utility of TAP as an adjunct drug for anaesthesia and analgesia in the rabbit. However, further studies are still needed before its use in the veterinary clinical practice