Influence of premedication with xylazine on the distribution and metabolism of intramuscularly administered ketamine in cats.

The pharmacokinetics and metabolism of intramuscularly administered ketamine (25 mg/kg) were determined in eight cats (group A). The effect of prior administration of the sedative agent xylazine hydrochloride (1 mg/kg intramuscularly) on the uptake distribution and metabolism of the drug was also investigated in another 10 cats (group B). It was found that xylazine significantly prolonged the duration of ketamine anaesthesia. In addition, xylazine not only prolonged the plasma half life of ketamine but significantly delayed the production of the primary metabolite of ketamine, norketamine. Studies on the urinary excretion of ketamine and norketamine in the cats in group B indicated that very little of the drug (less than 2.6 per cent) is excreted by this route in the initial 90 minutes after injection.