Ketamine, a cyclohexanone derivative, is a nonbarbiturate anesthetic agent that has been available in clinical practice for more than 40 years. Ketamine was first synthesized in 1962 and patented in Belgium in 1963. Ketamine, a potent non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, has a recognized unique therapeutic value in human and veterinary medicine as an anesthetic with analgesic properties. Ketamine is considered as one of the World Health Organisation (WHO) essential drugs for the management of refractory pain.