Tissue response to intramuscular and intraperitoneal injections of ketamine and xylazine in rats

Ketamine-xylazine is a widely accepted anesthetic combination for laboratory animals. Although frequently recommended for administration by intramuscular (IM) or intraperitoneal (IP) routes, the potential for tissue damage following either route of administration in the rat has not been investigated. This study evaluated tissue damage after IM use at two doses in Fischer 344 and Sprague-Dawley rats. Tissue reactions following IP injections of ketamine-xylazine were compared to lesions produced by IM injections in animals euthanatized on 1, 3 and 14 days post-injection. Results showed muscle necrosis present in nearly all ketamine-xylazine injected limbs. Intraperitoneal injections produced no significant lesions in the peritoneal cavity when careful IP injection techniques were used. Ketamine-xylazine should not be administered by the IM route for survival procedures in these two widely used strains of rats.