Acute obstructive uropathy in male C57Bl/6 mice after general anesthesia with fentanyl, midazolam and medetomidine

The selective alpha-2 adrenoreceptor agonist medetomidine is commonly used as a component of combination solutions for general anesthesia in rodents and small animals. However, it has also been reported to increase the risk of obstructive uropathy in male mice. Here we report that in a recent cohort of mice undergoing two sequential surgical procedures using the anesthetic combination of fentanyl, midazolam and medetomidine (FMM) for general anesthesia, 60% of the male mice developed severe obstructive uropathy within 48 hours of the second surgery. We also report one case of an older male mouse developing severe obstructive uropathy after a single general anesthesia with FMM. In a subsequent pilot study involving five male mice undergoing similar surgical procedures, also with two sequential surgeries, but using xylazine as the alpha-2 adrenoreceptor agonist in the narcotic combination, none of the animals developed obstructive uropathy in the post-operative period or thereafter. We suggest that replacement of medetomidine with xylazine should be considered for general anesthesia in male mice undergoing multiple successive anesthesia events or in for procedures in older males.