Ketamine in the Zoo Setting
Ketamine is a dissociative general anesthetic and an NMDA-receptor antagonist. It has been FDA-approve for use in humans, sub-human primates, and cats, although it has been useing many other species. The FDA-approve indications for cats include, “for restraint, or as the sole anesthetic agent for diagnostic, or minor, brief, surgical procedures that do not require skeletal muscle relaxation… and in subhuman primates for restraint.”1
Ketamine is use to induce general anesthesia in many species and as a constant rate infusion to provide analgesia and decrease the amount of inhalant use to maintain a surgical plane of anesthesia. It has been use intranasally in combination with midazolam in cats to induce sedation.2 Ketamine can inhibit NMDA receptors in the CNS and can decrease the wind-up pain effect. There is increasing interest in using it to prevent exaggerate pain associate with surgery or chronic pain states in animals.1
Ketamine: Pharmacology and Pharmacokinetics
Ketamine is a rapid-acting general anesthetic that has significant analgesic activity and a relative lack of cardiopulmonary depressant effects in healthy animals. It is thought to induce both anesthesia and amnesia by functionally disrupting the CNS through over-stimulating the CNS or inducing a cataleptic state. Ketamine binds the phencyclidine-binding site of the NMDA receptors, which prevents glutamate, an excitatory neurotransmitter, from stimulating these receptors.
Ketamine also interacts with opioid and monoaminergic receptors, which contributes to the antinociceptive effects of this drug. It is also believe that ketamine acts as an antagonist at the muscarinic receptor site, due to its anticholinergic effects (eg, bronchodilation, delirium, and sympathomimetic action); however, these symptoms may also be cause by direct stimulation of the sympathetic system.3 The thalamoneocortical system is depresse while the limbic system is activate. In cats, ketamine causes a slight hypothermic effect as body temperatures decrease on average by 1.6°C after high anesthetic doses (approximately 20 mg/kg).In most species, ketamine is metabolize in the liver principally by demethylation and hydroxylation. These metabolites, along with unchange ketamine, are eliminate in the urine.1