Esketamine (also (S)-ketamine or S(+)-ketamine) (brand name Ketanest S) is a general anaesthetic and a dissociative. It is the S(+) enantiomer of the drug ketamine, a general anaesthetic. Esketamine acts primarily as a non-competitive NMDA receptor antagonist, but is also a dopamine reuptake inhibitor. As of July 2014, it is in phase II clinical trials for treatment-resistant depression (TRD).
Esketamine is approximately twice as potent as racemic ketamine. It is eliminated from the human body more quickly than R(−)-ketamine or racemic ketamine, although R(−)-ketamine slows its elimination.
A number of studies have suggested that esketamine has a more medically useful pharmacological action than R(−)-ketamine or racemic ketamine. Esketamine inhibits dopamine transporters eight times more than R(−)-ketamine. This increases dopamine activity in the brain. At doses causing the same intensity of effects, esketamine is generally considered to be more pleasant by patients. Patients also generally recover mental function more quickly after being treated with pure esketamine, which may be a result of the fact that it is cleared from their system more quickly.
Esketamine has an affinity for the PCP binding site of the NMDA receptor 3-4 times higher than that of R(−)-ketamine. Unlike R(−)-ketamine, esketamine does not bind significantly to sigma receptors. Esketamine increases glucose metabolism in frontal cortex, while R(−)-ketamine decreases glucose metabolism in the brain. This difference may be responsible for the fact that esketamine generally has a more dissociative or hallucinogenic effect while R(−)-ketamine is reportedly more relaxing. However, other studies have found no difference between the isomers in the patient's level of vigilance.
Potential use as an antidepressant
Johnson & Johnson is developing a nasal spray formulation of esketamine as a treatment for depression in patients that have been unresponsive to other antidepressants in the United States. As of July 2014, phase II clinical trials of intranasal esketamine sponsored by the Johnson & Johnson subsidiary Janssen Pharmaceutica are underway. Other pharmaceutical companies are also developing new antidepressant drugs that act similarly to ketamine, including Naurex's rapastinel (GLYX-13) and NRX-1074, Cerecor's CERC-301, and VistaGen's AV-101.
Although most studies suggest that esketamine is preferable for medical uses, a 2013 study found that the antidepressant effect of R(−)-ketamine lasted longer than those of S(+)-ketamine in mice.
- Agonists: Adamantanes: Amantadine
- Rimantadine; Aminotetralins: 7-OH-DPAT
- UH-232; Benzazepines: 6-Br-APB
- SKF-83,959; Ergolines: Bromocriptine
- Pergolide; Dihydrexidine derivatives: 2-OH-NPA
- Adrogolide (ABT-431, DAS-431)
- Doxanthrine; Others: A-68930
- Salvinorin A
- Antagonists: Competitive antagonists: AP5 (APV)
- Midafotel (d-CPPene)
- Selfotel; Noncompetitive antagonists: ARR-15,896
- Zinc; Uncompetitive pore blockers: 2-MDP
- Methadone (Levomethadone)
- Methorphan (Dextromethorphan
- Morphanol (Dextrorphan
- Nitrous oxide
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- Kynurenic acid
- Licostinel (ACEA-1021)
- MRZ 2/576
- ZD-9379; NR2B subunit antagonists: Besonprodil
- CERC-301 (MK-0657)
- CO-101,244 (PD-174,494)
- Traxoprodil; Polyamine site antagonists: Arcaine
- Co 101676
- Huperzine A
- Ro 25-6981; Unclassified/unsorted antagonists: Bumetanide
- Diethyl ether
- Flufenamic acid
- Niflumic acid