Effects of Midazolam/Dexmedetomidine with Buprenorphine or Extended-release Buprenorphine Anesthesia in C57BL/6 Mice

The effects of commonly used injectable combinations of anesthetics such as ketamine and xylazine, with or without acepromazine, vary widely across individuals, have a shallow-dose response curve, and do not provide long-term analgesia. These drawbacks indicate the importance of continuing efforts to develop safe and effective injectable anesthetic combinations for mice. In this study, a series of experiments was designed to validate the use of dexmedetomidine and midazolam to provide chemical restraint for nonpainful procedures and the addition of buprenorphine or extended-release buprenorphine to reliably provide a surgical plane of anesthesia in C57BL/6J mice. Loss of consciousness was defined as the loss of the righting reflex (LORR); a surgical plane of anesthesia was defined as the LORR and loss of pedal withdrawal after application of a 300 g noxious stimulus to a hind paw. The combination of intraperitoneal 0.25 mg/kg dexmedetomidine and 6 mg/kg midazolam produced LORR, sufficient for nonpainful or noninvasive procedures, without achieving a surgical plane in 19 of 20 mice tested. With the addition of subcutaneous 0.1 mg/kg buprenorphine or 1 mg/kg buprenorphine-ER, 29 of 30 mice achieved a surgical plane of anesthesia. The safety and efficacy of the regimen was then tested by successfully performing a laparotomy in 6 mice. No deaths occurred in any trial, and, when administered 1 mg/kg atipamezole IP, all mice recovered their righting reflex within 11 min. The anesthetic regimen developed in this study is safe, is reversible, and includes analgesics that previous studies have shown provide analgesia beyond the immediate postsurgical period. Buprenorphine-ER can be safely substituted for buprenorphine for longer-lasting analgesia.