Ketamine and xylazine for surgical anesthesia in rats.

The responses of 2 inbred strains of rats to intramuscular doses of ketamine and xylazine, singly and in combination, were studied. A synergistic effect was observed when the 2 drugs were administered together, which resulted in anesthesia with extended analgesia and immobility. Anesthesia was achieved in most rats given 87 mg ketamine/kg of body weight and 13 mg xylazine/kg, beginning 10 to 15 minutes after simultaneous injection and lasting 15 to 30 minutes, then followed by a relatively long period of immobility (mean, 3.8 hours) and reduced responsiveness to external stimuli. Some rats required up to twice this dose for adequate surgical anesthesia. Total doses (initial and supplemental) of up to 3 times the amount were administered with apparent safety.