NMDA receptor antagonist

NMDA receptor antagonists are a class of drugs that work to antagonize, or inhibit the action of, the N-Methyl-D-aspartate receptor (NMDAR). They are commonly used as anesthetics for animals and humans; the state of anesthesia they induce is referred to as dissociative anesthesia. Several synthetic opioids function additionally as NMDAR-antagonists, such as pethidine, levorphanol, methadone, dextropropoxyphene, tramadol and ketobemidone. Some NMDA receptor antagonists, such as ketamine, dextromethorphan (DXM), phencyclidine (PCP), methoxetamine (MXE), and nitrous oxide (N2O), are sometimes used as recreational drugs, for their dissociative, hallucinogenic, and euphoriant properties. When used recreationally, they are classified as dissociative drugs. NMDA receptor antagonists induce a state called dissociative anesthesia, marked by catalepsy, amnesia, and analgesia. Ketamine is a favored anesthetic for emergency patients with unknown medical history and in the treatment of burn victims because it depresses breathing and circulation less than other anesthetics. Dextrorphan, a metabolite of dextromethorphan (one of the most commonly used cough suppressants in the world), is known to be an NMDA receptor antagonist. Numerous detrimental symptoms are linked to depressed NMDA receptor function. For example, NMDA receptor hypofunction that occurs as the brain ages may be partially responsible for memory deficits associated with aging. Schizophrenia may also have to do with irregular NMDA receptor function (the glutamate hypothesis of schizophrenia). Increased levels of another NMDA antagonist, kynurenic acid, may aggravate the symptoms of schizophrenia, according to the "kynurenic hypothesis". NMDA receptor antagonists can mimic these problems; they sometimes induce "psychotomimetic" side effects, symptoms resembling psychosis. Such side effects caused by NMDA receptor inhibitors include hallucinations, paranoid delusions, confusion, difficulty concentrating, agitation, alterations in mood, nightmares, catatonia, ataxia, anesthesia, and learning and memory deficits.