Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist, used as a tranquiliser/anaesthetic in cats. It is an important agent for analgesia in cattle. At high, fully anesthetic level doses, ketamine has also been found to bind to opioid μ receptors and sigma receptors.
Like other drugs of this class such as tiletamine and phencyclidine (PCP), it induces a state referred to as "dissociative anesthesia".
Ketamine has a rapid pharmacological action characterised by profound analgesia, mild cardiac stimulation, normal pharyngeal-laryngeal reflexes and mild respiratory depression. It produces cataleptic anaesthesia (dissociative anaesthesia). It causes complex reactions in the brain depressing certain areas and stimulating others, which enables it to anesthetize and cause seizures in overdose. It increases the release of dopamine and noradrenaline which are excitatory and increase the release or serotonin, which is a depressant. It produces paralysis with some muscle rigidity, good analgesia, complete amnesia. Many reflexes are retained; swallowing, coughing, pedal, corneal, laryngeal, however the animal does not blink and the cornea should be kept lubricated during long operations.
Ketamine can be used in isolation or in combination with other drugs such as xylazine. Its use is contraindicated in chronic renal disease. It may have a role in "resetting" of the central nervous system in maladaptive pain states. Ketamine can be used for routine surgical procedures when administered in combination with diazepam, medetomidine or xylazine for desexing.
Recommended dosages in cattle is 5-10 mg/kg as an IV, I or SQ injection. Intramuscular injections cause pain at the injection site, and it is recommended to be given IV or SQ, or rapidly IM.
- Baldridge SL et al (2011) Pharmacokinetics and physiologic effects of intramuscularly administered xylazine hydrochloride-ketamine hydrochloride-butorphanol tartrate alone or in combination with orally administered sodium salicylate on biomarkers of pain in Holstein calves following castration and dehorning. Am J Vet Res 72(10):1305-1317