Faster immobilization and recovery with remimazolam compared to midazolam in medetomidine-butorphanol balanced anesthesia in male Sprague-Dawley rats: a randomized crossover study

Background

Balanced injectable anesthesia combining an α2-adrenoceptor agonist, a benzodiazepine, and an opioid is widely used in laboratory rodents because it provides sedation, muscle relaxation, and analgesia through complementary pharmacological mechanisms. In Japan, a mixture of medetomidine, midazolam, and butorphanol (MMB) is commonly used as an injectable anesthetic regimen in mice and rats. Remimazolam is an ultra-short-acting benzodiazepine that is rapidly metabolized by tissue esterases and produces no active metabolites. Because of its rapid metabolism and predictable pharmacokinetic profile, remimazolam has attracted attention as a sedative agent in clinical anesthesia and procedural sedation. Replacing midazolam with remimazolam generates a novel balanced anesthetic combination consisting of medetomidine, remimazolam, and butorphanol (MRB). Although this regimen has been investigated in mice, its anesthetic characteristics in rats have not yet been fully evaluated. The present study aimed to compare the anesthetic and physiological effects of MMB and MRB anesthesia in Sprague-Dawley (SD) rats.