Evaluation of a combination of alfaxalone with medetomidine and butorphanol for inducing surgical anesthesia in laboratory mice

The anesthetic effects of alfaxalone were investigated in mice. Mice were administered alfaxalone (100 mg/kg) alone or the combinations of 0.3 mg/kg of medetomidine and 5 mg/kg of butorphanol with alfaxalone at doses of 20 mg/kg (M/B/A20), 40 mg/kg (M/B/A40), 60 mg/kg (M/B/A60), or 80 mg/kg (M/B/A80). Control mice received 0.3 mg/kg of medetomidine, 4 mg/kg of midazolam, and 5 mg/kg of butorphanol (M/M/B). Each drug was administrated by intraperitoneal (IP) or subcutaneous (SC) routes. M/M/B IP did not achieve surgical anesthesia but M/M/B SC achieved surgical anesthesia within 10 min after administration and maintained anesthesia for 45 min. The anesthetic scores were very low after IP or SC administration of alfaxalone alone. M/B/A20 IP and SC did not achieve surgical anesthesia. M/B/A40 IP did not achieve surgical anesthesia but M/B/A40 SC achieved surgical anesthesia within 10 min after administration and maintained anesthesia for 35 min. M/B/A60 SC achieved surgical anesthesia within 5 min after administration and maintained anesthesia for 75 min. By contrast, M/B/A60 IP did not achieve surgical anesthesia. M/B/A80 SC achieved surgical anesthesia within 5 min after administration and maintained anesthesia for 85 min. By contrast, M/B/A80 IP did not achieve surgical anesthesia and one mouse died about 10 min after drug administration. Administration of atipamezole rapidly reversed anesthesia induced by M/B/A60 in mice. These results suggest that M/B/A60 SC, an alfaxalone-based combination, is suitable for inducing surgical anesthesia in laboratory mice.