Norketamine, or ''N''-desmethylketamine, is the major
active metabolite An active metabolite is an active form of a drug after it has been processed by the body.
Metabolites of drugs
An active metabolite results when a drug is metabolized by the body into a modified form which continues to produce effects in the body ...
of
ketamine
Ketamine is a dissociative anesthetic used medically for induction and maintenance of anesthesia. It is also used as a recreational drug. It is one of the safest anesthetics, as, in contrast with opiates, ether, and propofol, it suppresses ne ...
, which is formed mainly by
CYP3A4
Cytochrome P450 3A4 (abbreviated CYP3A4) () is an important enzyme in the body, mainly found in the liver and in the intestine. It oxidizes small foreign organic molecules (xenobiotics), such as toxins or drugs, so that they can be removed from t ...
.
Similarly to ketamine, norketamine acts as a
noncompetitive 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 ...
(K
i = 1.7
μM
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American spelling), also commonly known as a micron, is a unit of length in the International System of Unit ...
and 13 μM for (''S'')-(+)-norketamine and (''R'')-(–)-norketamine, respectively),
but is about 3–5 times less potent as an
anesthetic
An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia — in other words, to result in a temporary loss of sensation or awareness. They may be divided into two ...
in comparison.
Also, similarly again to ketamine, norketamine binds to the
μ- and
κ-opioid receptor
The κ-opioid receptor or kappa opioid receptor, abbreviated KOR or KOP, is a G protein-coupled receptor that in humans is encoded by the ''OPRK1'' gene. The KOR is coupled to the G protein Gi/G0 and is one of four related receptors that bind op ...
s.
Relative to ketamine, norketamine is much more potent as an
antagonist
An antagonist is a character in a story who is presented as the chief foe of the protagonist.
Etymology
The English word antagonist comes from the Greek ἀνταγωνιστής – ''antagonistēs'', "opponent, competitor, villain, enemy, riv ...
of the
α7-nicotinic acetylcholine receptor, and produces rapid
antidepressant
Antidepressants are a class of medication used to treat major depressive disorder, anxiety disorders, chronic pain conditions, and to help manage addictions. Common side-effects of antidepressants include dry mouth, weight gain, dizziness, hea ...
effects in
animal model
An animal model (short for animal disease model) is a living, non-human, often genetic-engineered animal used during the research and investigation of human disease, for the purpose of better understanding the disease process without the risk of ha ...
s which have been reported to correlate with its activity at this receptor.
However, norketamine is about 1/5 as potent as ketamine as an antidepressant in mice as per the
forced swim test
The behavioural despair test (or Porsolt forced swimming test) is a test, centered on a rodent's response to the threat of drowning, whose result has been interpreted as measuring susceptibility to negative mood. It is commonly used to measure the ...
, and this seems also to be in accordance with its 3–5-fold reduced comparative potency ''
in vivo
Studies that are ''in vivo'' (Latin for "within the living"; often not italicized in English) are those in which the effects of various biological entities are tested on whole, living organisms or cells, usually animals, including humans, and ...
'' as an NMDA receptor antagonist.
Norketamine is metabolized into
dehydronorketamine
Dehydronorketamine (DHNK), or 5,6-dehydronorketamine, is a minor metabolite of ketamine which is formed by dehydrogenation of its metabolite norketamine. Though originally considered to be inactive, DHNK has been found to act as a potent and sele ...
and
hydroxynorketamine
Hydroxynorketamine (HNK), or 6-hydroxynorketamine, is a minor metabolite of the anesthetic, dissociative, and antidepressant drug ketamine. It is formed by hydroxylation of the intermediate norketamine, another metabolite of ketamine. As of l ...
, which are far less or negligibly active as NMDA receptor antagonists in comparison,
but retain activity as potent antagonists of the α
7-nicotinic acetylcholine receptor.
References
Arylcyclohexylamines
Antidepressants
Chloroarenes
Dissociative drugs
General anesthetics
Human drug metabolites
Kappa-opioid receptor agonists
Ketones
Mu-opioid receptor agonists
Nicotinic antagonists
NMDA receptor antagonists
Sedatives
{{Analgesic-stub