Anaesthetic effects of alfaxalone administered intraperitoneally alone or combined with dexmedetomidine and fentanyl in the rat

Alfaxalone is a neuroactive steroid used as a general anaesthetic in several species including dogs, cats, rabbits and ferrets. It has a wide margin of safety and a similar anaesthetic profile to propofol. To increase its aqueous solubility, a new formulation with cyclodextrins has been marketed recently. The objective of this study was to evaluate the anaesthetic effect of several doses of alfaxalone alone, considering differences between sexes, and alfaxalone combined with dexmedetomidine and fentanyl in the rat administered by the intraperitoneal route. A total of 40 Sprague Dawley rats, involved in three studies, were used. Firstly, 25, 35 and 45？mg kg–1 of alfaxalone alone were tested. In a second study, alfaxalone (25？mg kg–1, females; 75？mg kg–1, males) was combined with dexmedetomidine (0.05？mg kg–1). Finally, alfaxalone (20？mg kg–1, females; 60？mg kg–1, males) was combined with dexmedetomidine (0.05？mg kg–1) and fentanyl (0.1？mg kg–1). Times of onset and duration of anaesthesia, and analgesia, deemed as losing of withdrawal pedal reflex, were recorded. Alfaxalone alone produced a 2？- to 3-fold longer time of anaesthesia in females, although surgical anaesthesia was not achieved in either sex. The addition of dexmedetomidine and fentanyl to alfaxalone produced a similar time of analgesia as well as increased time of anaesthesia in both sexes. In conclusion, alfaxalone produces light anaesthesia in rats, and males required a higher dose. The combination with other sedatives or analgesics, such as dexmedetomidine or fentanyl, allows a more prolonged anaesthesia with analgesic effects, potentially suitable for invasive procedures