Relative to esketamine, arketamine possesses 4 to 5 times lower affinity for the PCP site of the NMDA receptor.[2][6] In accordance, arketamine is significantly less potent than racemic ketamine and especially esketamine in terms of anesthetic, analgesic, and sedative-hypnotic effects.[6] Racemic ketamine has weak affinity for the sigma receptor, where it acts as an agonist, whereas esketamine binds negligibly to this receptor, and so the sigma receptor activity of racemic ketamine lies in arketamine.[7] It was suggested that this action of arketamine may play a role in the hallucinogenic effects of racemic ketamine and that it may be responsible for the lowering of the seizure threshold seen with racemic ketamine.[7] However several subsequent studies have indicated that esketamine is more likely to induce dissociative events,[8][9] while studies in patients undergoing electroconvulsive therapy suggested that esketamine is a potent inducer of seizures.[10] Esketamine inhibits the dopamine transporter about 8-fold more potently than does arketamine, and so is about 8 times more potent as a dopamine reuptake inhibitor.[11] Arketamine and esketamine possess similar potency for interaction with the muscarinic acetylcholine receptors.[12]
Novel antidepressant
Arketamine appears to be more effective as a rapid-acting antidepressant than esketamine in preclinical research.[13]
A study conducted in mice found that ketamine's antidepressant activity is not caused by ketamine inhibiting NMDAR, but rather by sustained activation of a different glutamate receptor, the AMPA receptor, by a metabolite, (2R,6R)-hydroxynorketamine; as of 2017 it was unknown if this was happening in humans.[15][16] Arketamine is an AMPA receptor agonist.[17]
Paradoxically, arketamine shows greater and longer-lasting rapid antidepressant effects in animal models of depression relative to esketamine.[13][18][14] It has been suggested that this may be due to the possibility of different activities of arketamine and esketamine and their respective metabolites at the α7-nicotinic receptor, as norketamine and hydroxynorketamine are potent antagonists of this receptor and markers of potential rapid antidepressant effects (specifically, increased mammalian target of rapamycin function) correlate closely with their affinity for it.[19][20][21] The picture is unclear however, and other mechanisms have also been implicated.[14]
^ abBarash P, Cullen BF, Stoelting RK, Cahalan M, Stock MC, Ortega R (28 March 2012). Clinical Anesthesia. Lippincott Williams & Wilkins. pp. 456–. ISBN978-1-4511-4795-7.
^Vollenweider FX, Leenders KL, Oye I, Hell D, Angst J (February 1997). "Differential psychopathology and patterns of cerebral glucose utilisation produced by (S)- and (R)-ketamine in healthy volunteers using positron emission tomography (PET)". European Neuropsychopharmacology. 7 (1): 25–38. doi:10.1016/S0924-977X(96)00042-9. PMID9088882. S2CID26861697.
^Engelhardt W (March 1997). "[Recovery and psychomimetic reactions following S-(+)-ketamine]". Der Anaesthesist. 46 (Suppl 1): S38–S42. doi:10.1007/pl00002463. PMID9163277. S2CID24966884.
^Zavorotnyy M, Kluge I, Ahrens K, Wohltmann T, Köhnlein B, Dietsche P, et al. (December 2017). "S -ketamine compared to etomidate during electroconvulsive therapy in major depression". European Archives of Psychiatry and Clinical Neuroscience. 267 (8): 803–813. doi:10.1007/s00406-017-0800-3. PMID28424861. S2CID22725552.
^Kim JW, Suzuki K, Kavalali ET, Monteggia LM (January 2024). "Ketamine: Mechanisms and Relevance to Treatment of Depression". Annu Rev Med. 75: 129–143. doi:10.1146/annurev-med-051322-120608. PMID37729028.