Evaluation of a modified triple-combination anesthesia using dexmedetomidine in mice

Ketamine is a widely used anesthetic in animal research, but its use is strictly regulated in several countries, including Japan and China. As an alternative, the medetomidine-midazolam-butorphanol (MMB) combination is commonly used in Japan. However, medetomidine is a racemic mixture containing the inactive R-enantiomer, which may reduce anesthetic predictability and safety.

The aim of the study was to evaluate the efficacy and safety of a modified anesthetic combination (dMMB), in which dexmedetomidine replaces medetomidine, across three commonly used mouse strains (ICR, C57BL/6, BALB/c).

Male and female mice were administered either MMB or dMMB subcutaneously. Anesthetic depth, recovery profiles, heart rate, SpO₂, body temperature, ocular opacity, and blood glucose levels were assessed. Atipamezole was used to reverse anesthesia, and thermoregulatory recovery was monitored postinjection.

dMMB produced similar anesthetic depth to MMB, with faster and more consistent recovery, particularly in males. Body temperature recovery was significantly enhanced in dMMB-treated B6 males. No significant differences in side effects (ocular opacity or blood glucose levels) were observed between protocols, though strain-specific glucose elevations were noted in dMMB-treated males.

dMMB is a safe, effective, and ketamine-free injectable anesthetic protocol, offering advantages in recovery and thermoregulation. It may be a valuable alternative in research settings where ketamine is restricted and medetomidine may become unavailable.