Ketamine is a lipophilic, general anesthetic. When given at subanesthetic doses, it also has been found to be an effective analgesic, with efficacy in cancer-associated neuropathic pain, ischemic pain, and regional pain syndromes. It can be administered orally, intravenously, subcutaneously, and topically, and interacts with several receptors important in pain management, most importantly the N-methyl-D aspartate (NMDA) receptor. Blockade of the NMDA receptor is associated with reversal of opioid tolerance. Ketamine is metabolized via cytochrome P450 3A4, although no significant interactions have been reported. Ketamine is considered one of the World Health Organization (WHO) essential drugs for the management of refractory pain.