Showing posts with label psychedelics. Show all posts
Showing posts with label psychedelics. Show all posts

Friday, June 3, 2016

Are Hallucinogens The New Miracle Drugs?

See Attribution 1 for full reference




Steve Jobs:  "Taking LSD was a profound experience, one of the most important things in my life.  LSD shows you that there's another side to the coin, and you can't remember it when it wears off, but you know it.  It reinforced my sense of what was important - creating things instead of making money, putting things back into the stream of history and of human consciousness as much as I could."  (ref 1)

Woodstock (Chip Monck):  "To get back to the warning that I received. You may take it with however many grains of salt that you wish. That the brown acid that is circulating around us isn't too good. It is suggested that you stay away from that. Of course it's your own trip. So be my guest, but please be advised that there is a warning on that one, OK?" (ref 2)




Warning: The final few paragraphs of this post contain language that some may find offensive.  I included it for a reason.   In 30 years of practice and in my real life - I have found that many people talk this way.  If profanity offends you don't read the end of this post.



Everywhere I turn these days - whether it is a blog or more traditional media I am struck by the same stories on hallucinogens.  If you believe what you read out there, hallucinogens are magical drugs in that they are almost totally benign, consciousness expanding, and they can treat your anxiety or your depression.  They have been actively discriminated against like other illegal drugs and that is the only reason we have not done the research to prove that they can treat many problems.  Back in the 1970's we would have said that "The Man" is restricting access to valuable consciousness expanding drugs and if "The Man" was overthrown - the world would be a much better place.  I have briefly reviewed the same lines of rhetoric that occur with cannabis.  I have not heard similar arguments with ketamine, probably because fewer people have experience with it and it is a more difficult drug to use, even in a medical setting where the drug has a known concentration and purity.

Hallucinogens are a diverse set of compounds with a number of analogues of the parent compounds for each basic structure.  The DSM-5 does very little in terms of organizing the category other than saying that it might make sense to classify the dissociative hallucinogens like PCP and ketamine as a separate category from more traditional hallucinogens like LSD.  The DSM-5 does very little to attempt to classify the wide array of hallucinogens that are available at this point in time.  Some authors (3-6) use the term serotonergic or classic psychedelics such as LSD, DMT, and psilocybin (and see above graph).  I think it makes sense to classify any drug taken for the express purpose of creating hallucinations - a hallucinogen.  Drugs with secondary hallucinatory effects like alcohol, cannabis, and stimulants remain in unique categories because they can all cause hallucinations but they are generally not taken for that purpose,  More scientific classification approaches that are generally based on chemical structure are available in standard addiction texts.

As an addiction  psychiatrist, my experience is that hallucinogens are problematic drugs from a number of perspectives.  It is rare to see a pure hallucinogen user, at least until someone discovered that using high dose dextromethorphan (DXM) reliably produces hallucinations and delirium, is widely available, and inexpensive.  To that subgroup of patients many of them have a very difficult time stopping DXM.  The other problem with that drug is that excessive use of DXM in the predisposed person is common and the margin between the hallucinatory experience, toxicity and lethal overdose is not well characterized probably due to pharmacokinetic variability among subjects.  Reports of lethal ingestions in the medical literature are rare (5).  The hallucinogenic effect of DXM is from NMDA and PCP1 receptor antagonism.  DXM is metabolized by hepatic CYP2D6 so that other drugs that are inhibitors and poor metabolizer status may lead to unexpectedly higher levels of the compound in the plasma.  DXM  is also a serotonin reuptake inhibitor and a 5-HT1 direct agonist and can cause serotonin syndrome another potential cause of death when used with other serotonergic drugs.  PCP is another exception.  In my experience both PCP and DXM users are much more likely to use those drugs in an uncontrolled manner and addictive manner than other types of hallucinogens. There are seemingly rare but significant and in some cases fatal side effects from hallucinogens.  From a mental health standpoint, addiction specialists and general psychiatrists encounter patients with significant ongoing panic symptoms and perceptual disturbances that they attribute to the side effects of these medications.  The question is what is the frequency of these side effects and their significance?  An associated question is have there been any definitive studies?

Most of the recent epidemiology of hallucinogens has come from Krebs and Johansen.  Their 2013 study in PLOS was widely quotes in the news media as illustrating that classic hallucinogens are benign substances with little health risk.  Their work is based on the annual NSDUH survey of drug use in Americans.  They look at two small (N=192, N=156) cohorts of pure hallucinogen users in the NSDUH survey.  They outline the limited nature of this investigation based on the survey questions and the fact that this is a survey.  They cite other literature looking at people given LSD in clinical trials and other research and conclude that there is very little evidence for lasting side effects.  As an example, they could not corroborate that at least some people who taken hallucinogens have persistent problems with anxiety, panic attacks, or perceptual disturbances.  These are familiar themes in the new research on LSD noted in several of the additional references.  As a starter,  I read the articles (7-10) and came up with several unanswered questions.  Some are obvious in a technical sense and some are not so obvious.  Rather than get into a detailed critique of this and other papers, I thought I would outline what I see as missing in the claims made for the benign side effects profiles and efficacy of these drugs and look at more details in subsequent posts.


Efficacy for what?

These drugs in the broadest sense are not used to treat any specific collection of symptoms or syndromes.  Their popular indication for use has changed very little since the 1960s (3) and that is "mystical experiences, curiosity, and introspection."  At that level there is no medical indication for use.  They are being used to produce an altered state of consciousness like alcohol or any other recreational drug.  At that level the issue resembles in many ways medical cannabis, with the exception that cannabis seems to have some very preliminary evidence that it might be useful for some medical problems.  No such data exists for hallucinogens and psychedelics, but that is not for a lack of effort.  A recent meta-analysis discussed in Nature suggests that alcoholics treated with LSD are more likely to stay abstinent than those who are not.  The original experiments done in the 1970s, found no such correlation.  A recent paper in Lancet Psychiatry discusses application for the existential anxiety of the terminally ill and to facilitate psychotherapy.    So far the medical indications seem to be a bit of a stretch.  Using cannabis as the prototype, it seems that many parallel arguments are being made for hallucinogens.  From a rhetorical standpoint it is interesting that a common antipsychiatry criticism is that psychiatry has medicalized life in order to proliferate diagnoses and make more money for pharmaceutical companies.  Nobody seems to have any problems with cannabis or hallucinogen proponents medicalizing life in order to provide a useful venue for cannabis or hallucinogens.

As an adjunct for psychotherapy? 

There is a new recent review (14) of psilocybin and MDMA as assistive modalities in psychotherapy.  My read of this review is that the authors are proponents of these therapies.  They cite the lack of useful current therapies as a reason for exploring the therapeutic aspects of psychedelics.  That may be true to some extent but the usefulness of current therapies also depends on how broad the access is.  When I do a new assessment, I don't get the same global acceptance of therapy that some in the popular press suggest.  The impression I get is that the psychotherapy experience that most people get is suboptimal at best - and not because of the therapeutic modality.  It is often the technique of the therapist, economic considerations, managed care constraints, and/or the lack of any results.  The authors suggest that exploring psychedelics in these settings might offer better results and faster results.  I can't help but think about how therapy in real life, doesn't resemble what the psychotherapy in clinical trials is like.  Many people in managed care settings get two or three cursory sessions and they are discharged as doing better.  What happens if psychedelic assisted psychotherapy occurs in a managed care setting?  My guess is that the complex therapy is eliminated and the sessions where the drug is administered is emphasized.  The conditions for therapy reviewed include cancer anxiety, addiction (alcohol, tobacco and cocaine) and obsessive-compulsive disorder for psilocybin and PTSD, anxiety from life-threatening situations, and social anxiety in autistic adults for for MDMA.  There is minimal detail on the psychotherapeutic technique apart from some lengthy sessions.  Problems with blinding in controlled trials are discussed as an issue.  Lower dose psychedelics as the active placebo don't work.   Preliminary successes and speculation about the effect of the psychedelics and what they might be doing are discussed.  The main argument seems to be that there is ample reason to continue research in psychedelics.    


What can be measured?

All clinical trials in psychiatry lack objective measurements of both illness and improvement.  In the case of psychedelics some of these standard problems are still there.  Standard rating scales for anxiety and depression are used in some of these trials.  There are additional instruments such as the Altered States of Consciousness Questionnaire (ASQ) and the Psychotomimetic States Inventory (PSI).  It seems that an interest in purportedly consciousness expanding drugs may finally get some psychiatrists interested in consciousness as a dynamic multidimensional entity independent of syndrome definitions.  The problem of course is that these states are all highly subjective and resistant to classification.  It also highlights the question: "Is the psychedelic drug +/- psychotherapy supposed to target a typical syndrome of anxiety or depression or is there some other purpose, like altering the conscious state in some fundamental way?".  If that is true, we really have no idea how that can be measured or translated into therapy.  I would also suggest that it is outside the purview of physicians and psychiatrists.  If it is effective, the one aspect of psychedelic assisted therapy that I thought would be very useful was that the patient only takes two or three doses of the drug over the course of psychotherapy and does not require a maintenance treatment.

Quality of subjective measurement aside, there is nothing more annoying to me as an interested reader than reading about a rating scale or questionnaire that is not readily available.  I need to know what the specific questions are on those instruments.  The statistics of the instrument is a secondary consideration.  As far as I can tell neither the ASQ or the PSI is readily available in a readable form.  I would go so far to encourage editors to suggest that in the original analysis of rating scales, questionnaires, and inventories include the scale as it was used with all of the direct wording and how it was rated.  If that data is not included the article is essentially worthless to any clinician who talks to patients.


Are we measuring dimensions of consciousness?

I have addressed the general lack of concern over human consciousness in psychiatry and medicine in general.  Human consciousness is generally regarded as a brain determined state, but we have no idea how that state arises from the underlying neurobiology.  There are plenty of theories and there is a scientific society dedicated to the study of human consciousness.  Consciousness is a highly subjective state and that makes it very difficult to study.  Even a basic consideration of experiencing the color red can be as complex as considering that each human being (every human being has a unique conscious state) can experience the color red in a unique way.  We all may be able to agree on a basic task that requires selecting the color red from other colors,  but beyond that we can never be completely sure of how other people experience colors or other physical properties or more complicated states like pain, depression, aging, or the opposite gender.  If all that is true about human consciousness - what would we expect to happen if we are taking a drug that alters our conscious state.  For research purposes, if we alter a conscious state and we really don't have a good way to measure a baseline conscious state - how can we detect what changes.  Are we going to depend strictly on self report of whatever comes to the person's mind?


Sweeping conclusions about the lack of toxicity?

Any pro-hallucinogen article will produce a steady stream of references looking at how benign these compounds are.  There are usually quotes about millions of doses consumed and no deaths from LSD or other psychedelics.  The authors generally assume that the methodologies being quoted are adequate indications of drug safety.  These arguments fail at two levels.  First, there is evidence in the literature from reasonable sources that LSD exposure is not entirely benign.  The 1986 Danish LSD Damages Laws is a case in point.  In this study, 400 patients treated with LSD between 1960 and 1973 were followed.  154 of these patients were compensated for long term harm with 2/3 of them having severe flashbacks.  There was also one homicide, 2 suicides, and 4 suicide attempts in the group (12).  There is the question of other sources such such as the DAWN system that looks at the number of emergency department visits (ED) per day due to substance use.  This system looks at annual use of substances by 18-25 years olds, how much they use on an average day and the number of ED visits per day due to a specific category of drugs.

See Attribution 2 for full reference.
         
In terms of drug safety and pharmacovigilance, there really has not been any with these drugs.  The side effects tend to be case reports, anecdotal, from settings where there is likely a bias to under report side effects, and from carefully run clinical trials.  In some cases researchers have a defined protocol for the safe design and running of clinical trials involving psychedelic drugs (15).

Medicine or recreational drug?

Cannabis legalization was basically dead in the water until the proponents adopted a political strategy that involved selling it as a medical treatment rather than a recreational drug.  The preferred path seems to be starting with terminal illnesses or illnesses for which there are no current good treatments.  Nobody ever seems to explore the question about why the legalization question doesn't seem to carry the argument on its own merit.  The arguments for the therapeutic use of hallucinogens seems to be following that same pathway.

More rights and politics?

Some of the pro-hallucinogen literature promotes the use of hallucinogens including the legal right of people to use hallucinogens.  I have no problem at all with activists trying to influence their favorite politicians in a way that they can more easily obtain their favorite intoxicant.  I do have a problem when activists start to write medical literature from that perspective.  I also think that an additional level of disclosure is needed at the editorial level.  Authors that argue for the availability of hallucinogens (or for that matter any recreational intoxicant) should disclose that as a potential conflict of interest by specific compounds.  An example would be: "Dr. Smith supports the widespread availability of LSD for both medical and recreational use".  Explicitly stating that potential conflict of interest, is every bit as important as stating that your research has been supported by a pharmaceutical company, but it is more difficult to track.    

Is there a better way to live?

There are always philosophical and ethical considerations.  As I hope to show in a future post, philosophers generally are not too interested in telling people how to live (although there are a few notable exceptions).  Psychiatrists certainly are not interested in that either no matter how much rhetoric is out there saying otherwise.  The arguments to use or try hallucinogens are of the general form that it may improve you in some way or offer you valuable insights.  It certainly may not or in the case of many leave them with a very negative residual memory of the personal experiment or some residual symptoms.  Much of the rhetoric is the old legalization argument: "If it really is that harmless, who shouldn't I have the freedom to use it?"  Add the corollary: "It is less dangerous than tobacco and alcohol!" and you have a full scale legalization argument on your hands.  This debate has become stereotypical these days and nobody seems to ever ask the question: "Is this a reasonable way to live?"  or  "Should people get high just because we can?"  Do you really have to take a drug to expand your consciousness or can you do something else?  Focusing on only the legal aspect and the freedom to use drugs short circuits that larger question and it is a very significant question.  Moreover - if your goal is expanding your consciousness how do you know that LSD is the best way to do that?  How do you know it is just not a complete waste of time - time that you may not have to waste?

There is a phrase that is popular in the drug using vernacular and that phrase is "fucked up."  It encompasses an entire spectrum from a highly desired state of intoxication to a very dysphoric state of toxic effects, withdrawal effects, and delirium.  Interview people at either end of the spectrum and they will declare: "I am really fucked up!" with varying prosody to suggest the end of the spectrum they perceive themselves to be at that given moment.  That is assuming that they are not too delirious to speak.  Use of the term highlights how subjective drug use is as well as the full spectrum of use.  It removes any pretense that a legal intoxicant will be used primarily in a therapist's office or a room full of intellectuals focused on expanding their consciousness.    We can't use a 10 point scale with the term on either end.  We are not really treating anything.  How many days during your life can you spend "fucked up" - whether or not the intoxicant is medically dangerous to you?  Probably not too many if you expect to have a work, a social and a family life where you depend on other people and they depend on you.  Probably not too many if you live in a dangerous environment like Minnesota and you have to decide at some point that you need to be wearing enough protective clothing outdoors to prevent frostbite, exposure, and death.

Hallucinogens or psychedelics are probably not the new miracle drugs simply because they have already been sold that way and it didn't work out.  As two authors (13) closer to the history of LSD put it:

"....In all likelihood acid will continue to ravage as many people as it liberates and deceive as many as it enlightens.  Whether it will play a more significant role in the future remains a matter of conjecture, for the psychedelic experience carries the impress of a constellation of social forces that are always shifting and up for grabs.  It's not over yet."  

My only qualifier is always that people with addictions will generally do worse.



George Dawson, MD, DFAPA



References:

1:  Walter Isaacson.  Steve Jobs.  Simon & Schuster.  New York. 2011. p 41.

2: Woodstock: Music from the Original Soundtrack and More. Cotillion Records. 1970.

3:  Glennon RA.  The pharmacology of hallucinogens and designer drugs.  in Principles of Addiction Medicine, Fourth Edition.  RK Ries, DA Fiellin, SC Miller, and R Saitz (eds); Wolters Kluwer/Lippincott Williams & Wilkins; Baltimore 2009: pp 215-230.

4:  Domino EF, Miller SC.  The pharmacology of dissociatives.  in Principles of Addiction Medicine, Fourth Edition.  RK Ries, DA Fiellin, SC Miller, and R Saitz (eds); Wolters Kluwer/Lippincott Williams & Wilkins; Baltimore 2009: pp 231-240.

5:  Pechnick RN, Cunningham KA.  Hallucinogens.  in Substance Abuse: A Comprehensive Textbook, Fifth Edition.  P Ruiz, E Strain (eds); Wolters Kluwer/Lippincott Williams & Wilkins; Baltimore 2011: pp 267-276.

6:  McCann UD.  PCP/Designer Drugs/MDMA. in Substance Abuse: A Comprehensive Textbook, Fifth Edition.  P Ruiz, E Strain (eds); Wolters Kluwer/Lippincott Williams & Wilkins; Baltimore 2011: pp 277-283.

7: Krebs TS, Johansen PØ. Psychedelics and mental health: a population study. PLoS One. 2013 Aug 19;8(8):e63972. doi: 10.1371/journal.pone.0063972. eCollection 2013. PubMed PMID: 23976938; PubMed Central PMCID: PMC3747247.

8: Johansen PØ, Krebs TS. Psychedelics not linked to mental health problems or suicidal behavior: a population study. J Psychopharmacol. 2015 Mar;29(3):270-9. doi: 10.1177/0269881114568039. Epub 2015 Mar 5. PubMed PMID: 25744618. 

9: Krebs TS, Johansen PØ. Reply letter: Mental health of people who have used classical psychedelics and no other illicit drugs. J Psychopharmacol. 2015 Sep;29(9):1036-40. PubMed PMID: 26649373. 

10: Krebs TS, Johansen PØ. Over 30 million psychedelic users in the United States. F1000Res. 2013 Mar 28;2:98. doi: 10.12688/f1000research.2-98.v1. eCollection 2013. PubMed PMID: 24627778; PubMed Central PMCID: PMC3917651.

11: Logan BK, Goldfogel G, Hamilton R, Kuhlman J. Five deaths resulting from abuse of dextromethorphan sold over the internet. J Anal Toxicol. 2009 Mar;33(2):99-103. PubMed PMID: 19239735.

12: Larsen JK. Neurotoxicity and LSD treatment: a follow-up study of 151 patients in Denmark. Hist Psychiatry. 2016 Jun;27(2):172-89. doi: 10.1177/0957154X16629902. Epub 2016 Mar 10. PubMed PMID: 26966135.

13:  Lee MA, Shlain B.  The Complete Social History of LSD: The CIA, The Sixties, and Beyond.  Grove Press, New York, 1985: p 294.

14: Mithoefer MC, Grob CS, Brewerton TD.  Novel psychopharmacological therapies for psychiatric disorders: psilocybin and MDMA. Lancet Psychiatry. 2016 May;3(5):481-8. doi: 10.1016/S2215-0366(15)00576-3. Epub 2016 Apr 5. Review. PubMed PMID: 27067625.

15: Johnson M, Richards W, Griffiths R. Human hallucinogen research: guidelines for safety. J Psychopharmacol. 2008 Aug;22(6):603-20. doi: 10.1177/0269881108093587. Epub 2008 Jul 1. Review. PubMed PMID: 18593734.




Attribution:

1:  Krebs TS and Johansen PØ. Over 30 million psychedelic users in the United States [version 1; referees: 2 approved]. F1000Research 2013, 2:98 (doi: 10.12688/f1000research.2-98.v1)

Copyright: © 2013 Krebs TS and Johansen PØ. This is an open access article distributed under the terms of theCreative Commons Attribution Licence, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2:  Figures 2 and 5 are from Substance Abuse and Mental Health Services Administration (SAMHSA) Emergency Department Data.

Sunday, May 8, 2016

Latest on Ketamine

(R,S)-ketamine


Ketamine has been prominent in the psychiatric literature and conferences for the past decade as a potential agent for both treatment resistant depression and a rapid antidepressant response.  In some communities ketamine infusion clinics are available where patient can go for a weekly infusion to maintain depression either in remission or a partial response.  At a cultural level, besides being a dissociative agent for anesthesia, ketamine is also in the collection of drugs known as club drugs and as such it is abusable.  Ketamine is not among the most commonly abused drugs.  The NSDUH survey puts lifetime abuse at about 1%.  In a practice of addiction psychiatry it is less likely to be used than LSD and much less likely to be used than dextromethorphan.  It may be one of many drugs used by polysubstance users at some point in their usage history.  Ketamine is also classified as a psychedelic drug or a drug that can cause hallucinogenic or dissociative experiences.  From the time their use was popularized there was a belief that these experiences could be potentially beneficial from the standpoint of personal growth and creativity, as an agent to enhance psychotherapy, or in some cases as an agent to treat psychiatric problems like alcoholism and depression.  Ketamine is currently a Schedule III non-narcotic drug on the DEA List of Controlled Substances.  My first professional exposure to the pharmacology of ketamine occurred in basic science courses in medical school in about 1983.  It was taught as part of the pharmacology of anesthesia agents.  It was taught as not being a first line drug at that point because of the side effects of dissociation and anesthesia.  Like most old medications there has been a recent revival of interest for rapid sedation of patients in emergency department settings.  In the linked report it had a more rapid onset of action than the usual agents, but also a significantly higher complication rate.

Alan Schatzberg, MD gave a presentation on ketamine at the University of Wisconsin Annual Update and Advances in Psychiatry in October 2013.  He presented data to show that the effects of intravenous ketamine were acute but not sustained.  Depressed unipolar subjects noticed the antidepressant effects within a few hours and they lasted about one week before returning to baseline depression scores on a standard Hamilton Depression Rating Scale.  In bipolar depression the effects last about 12 days.  He presented the results of an NIMH trial of ketamine in treatment resistant depression.  It was a small multisite trial that compared ketamine (N=47) to midazolam (N=25) as an active placebo.  The primary outcome measure was remission of depressive symptoms at 25 hours and the rates were 63.8% for ketamine versus 28% for midazolam.  Dizziness, blurred vision, nausea/vomiting, headache, and palpitations were the most common side effects acutely and at 24 hours.  There were no episodes of psychosis.  Longer term strategies were presented that might sustain the acute ketamine response including an oral form, repeated infusions, memantine, riluzole, lamotrigine, high dose d-cycloserine, and several new oral agents that were antagonists or partial allosteric modulators of the glutamate receptor, or partial agonist of the NMDA receptor glycine site.  Response to ketamine infusion at 2 hours was shown to be predictive of response and there was a 70% chance of relapse after repeated infusion but this sensitization did not occur at 2 week intervals.  Despite these limitations on therapy there is  Ketamine Advocacy Network that includes a quote about the coming ketamine today tidal wave and a page with this very dim view of psychiatric practice and the intellectual interests of the average or most (?) psychiatrists.  It is not clear to me who writes their pages or who their medical consultants are.

Barry Rittberg, MD gave a presentation at the Minnesota Psychiatric Society in May 2014 and reviewed the science, clinical trial data, and local protocols for ketamine infusions in Minnesota.  The major problems were short term benefit, unknown long term risk,  inability to drive that day,  psychotomimetic effects, and the 3-4 hour time commitment for the infusion.  The protocol discussed involved a 40 minute infusion with monitoring blood pressure, pulse and oxygen saturations every 15 minutes.  Treatments were given 3 days a week for three weeks.  In addition, insurance companies did not cover the treatment (and still don't).  The treatment is not FDA approved and therefore considered experimental by insurance companies.  

The main emphasis of research studies on ketamine and other agents is the potential importance of the glutamatergic system in the treatment of depression.  It also has a purported role in schizophrenia.  There was a good review in an excellent journal Clinical Pharmacokinetics that suggested the (S)-ketamine had a more favorable side effect profile than the racemate.  It was with that backdrop of information that I honed in on this article that popped up on my Facebook feed.  After the first few pages I knew that I was not going to be disappointed.

The authors of a Nature article (1) review the information in the above paragraphs as a rationale for their research and rapidly describe their series of experiments.  The animal research done in this paper is all rodent research to test the potential antidepressant, self-administration, drug discrimination, chronic corticosterone induced anhedonia, and motor coordination effects effects of various glutamatergic compounds.  All of these paradigms and much more are detailed in the supplementary and methods section of the online paper.  Tissue distribution and clearance of ketamine and metabolites was determined in both plasma and brain at 10, 30, 60, and 240 minutes post ketamine administration.

In the first set of experiments, the researchers showed that (R)-ketamine had greater antidepressant potency in three antidepressant predictive tasks - the mouse forced swim test (FST), the novelty-suppressed feeding task (NSF) and the learned helplessness task.  They also showed that this was not due to higher brain levels (R)-ketamine versus (S)-ketamine.  The NMDAR antagonist MK-801 was also shown to not exert the same effects as ketamine, suggesting that the mechanism was more complex than inhibition.  The most interesting part of this paper was the examination of ketamine metabolites and their potency as potential antidepressants.  Ketamine is metabolized by CYP3A and CYP2B6 hepatic enzymes mostly to norketamine, but a number of transformations including dehydrogenation, and hydroxylation to a broad array of metabolites as shown in the authors' graphic below (click on the graphic for a more readable version).

The HNK (hydroxynorketamine) metabolites are the major metabolites found in the plasma and brains of mice after ketamine administration and the plasma of humans.  When greater antidepressant effects were noted in female mice, it was determined that the levels of (2S,2S;2R,6R)-HNK were three times higher in females than males.  In order to confirm that this metabolite was the most potent, a deuterated form of ketamine was synthesized.  The deuteration significantly slowed the metabolism of the parent compound and the antidepressant effects were eliminated largely by blocking the formation of  (2S,2S;2R,6R)-HNK.  The (2R,6R)-HNK derived from (R)-ketamine was subsequently determined to be the most potent metabolite (as highlighted in the above metabolic map).

The authors went on to confirm that (2R,6R)-HNK increased glutamatergic signalling in a number of paradigms.  They also demonstrated that administration led to expected changes in AMPARS (α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors).  Drug discrimination and self-administration tests showed no tendency for self-administration with the (2R,6R)-HNK as opposed to ketamine.  In the same experiments ketamine was self administered and increased amounts were taken.   The (2R,6R)-HNK metabolite also did not cause motor incoordination or increased locomotion like ketamine did.

The implications of this paper are far reaching in terms of possible therapeutic agents.  It clarifies that the molecule involved in treating depression may be a significantly different structure than ketamine.  Second, that structure seems to have none of the side effects of the parent compound in animal models.  This paper also has implications for human research.  A search on HNK in the medical literature shows no evidence that it has ever been administered to humans.  A search on ClinicalTrials.gov shows no current research with the compound.  People are receiving infusions of ketamine for both chronic pain and chronic depression.  The infusions are done in clinics where patients need to monitored closely largely because of the side effects of ketamine.  The research done in this paper suggests that the administration of the active metabolite of ketamine may open the door for a less invasive and time intensive treatment for chronic depression.  I liked the idea that this paper discussed the relevant chemistry and pharmacology - undergraduate and medical school knowledge that is still relevant.  I also liked the idea that it potentially demystifies a hallucinogenic drug.  I have seen the newspaper headlines: "Club drugs to treat your depression."  I doubt that they will be replaced by: "(2R,6R)-HNK to treat your depression" anytime soon.

But the nullification of another urban drug legend is always a positive from my perspective.


George Dawson, MD, DFAPA      



References:

1: Zanos P, Moaddel R, Morris PJ, Georgiou P, Fischell J, Elmer GI, Alkondon M, Yuan P, Pribut HJ, Singh NS, Dossou KS, Fang Y, Huang XP, Mayo CL, Wainer IW, Albuquerque EX, Thompson SM, Thomas CJ, Zarate CA Jr, Gould TD. NMDAR inhibition-independent antidepressant actions of ketamine metabolites. Nature. 2016 May 4. doi: 10.1038/nature17998. [Epub ahead of print] PubMed PMID:27144355.

2: Peltoniemi MA, Hagelberg NM, Olkkola KT, Saari TI. Ketamine: A Review of Clinical Pharmacokinetics and Pharmacodynamics in Anesthesia and Pain Therapy. Clin Pharmacokinet. 2016 Mar 30. [Epub ahead of print] Review. PubMed PMID: 27028535.

Supplementary:

1:  The figure labelled Extended Data Figure 1 is from reference number 1 (above) and is used with permission from the Nature Publishing Group - license number 3863110054693 obtained on May 6, 2016.

2:  Shortly after writing this post I came across this reference suggesting the postsynaptic signalling mechanism responsible for the "ketamine" effect.  I have not read the article yet since it is not open access, but if they were really using ketamine to induce the effect it would be more interesting if they compared (2R,6R)-HNK to ketamine and other metabolites in this model.  It could provide confirmatory data on whether (2R,6R)-HNK is in fact the active metabolite.

Harraz MM, Tyagi R, Cortés P, Snyder SH. Antidepressant action of ketamine via mTOR is mediated by inhibition of nitrergic Rheb degradation. Mol Psychiatry. 2016 Mar;21(3):313-9. doi: 10.1038/mp.2015.211. Epub 2016 Jan 19. PubMed PMID: 26782056.