Norketamine, or N-desmethylketamine, is the major active metabolite of ketamine, which is formed mainly by CYP3A4.[1][2] Similarly to ketamine, norketamine acts as a noncompetitiveNMDA receptor antagonist (Ki = 1.7 μM and 13 μM for (S)-(+)-norketamine and (R)-(–)-norketamine, respectively),[1][3] but is about 3–5 times less potent as an anesthetic in comparison.[2][4] Also, similarly again to ketamine, norketamine binds to the μ- and κ-opioid receptors.[5] Relative to ketamine, norketamine is much more potent as an antagonist of the α7-nicotinic acetylcholine receptor, and produces rapid antidepressant effects in animal models which have been reported to correlate with its activity at this receptor.[6] However, norketamine is about 1/5 as potent as ketamine as an antidepressant in mice as per the forced swim test, and this seems also to be in accordance with its 3–5-fold reduced comparative potency in vivo as an NMDA receptor antagonist.[7] Norketamine is metabolized into dehydronorketamine and hydroxynorketamine, which are far less or negligibly active as NMDA receptor antagonists in comparison,[2] but retain activity as potent antagonists of the α7-nicotinic acetylcholine receptor.[8][9]
^Sałat K, Siwek A, Starowicz G, Librowski T, Nowak G, Drabik U, Gajdosz R, Popik P (2015). "Antidepressant-like effects of ketamine, norketamine and dehydronorketamine in forced swim test: Role of activity at NMDA receptor". Neuropharmacology. 99: 301–7. doi:10.1016/j.neuropharm.2015.07.037. PMID26240948. S2CID19880543.
