Why this poison is interesting

Almost every page in this library describes a drug whose danger is concentrated into a single exposure. Ketamine's UK label describes the opposite situation in a single sentence: ketamine has a wide margin of safety; several instances of unintentional administration of overdoses of ketamine (up to 10 times that usually required) have been followed by prolonged but complete recovery.¹ There is no other entry here whose label says anything comparable, and the whole overdose section of that document consists of that sentence plus advice to support ventilation.¹

That acute safety is the reason the chronic harm was missed for so long. A drug that does not kill people acutely does not generate the case reports and coroner's referrals that build a toxicological literature. Chu and colleagues reported ten young ketamine users presenting to two regional hospitals in Hong Kong with lower urinary tract symptoms, contracted bladders and other urinary tract abnormalities, noting that these types of findings had never been reported before in ketamine abusers.³ That was 2007 — decades after the drug entered recreational use.

The third reason is what happened when somebody looked properly. Winstock and colleagues surveyed a dance-music population and found that of 1285 respondents reporting ketamine use in the last year, 26.6% reported urinary symptoms, with symptoms significantly related to both dose and frequency of use.² A quarter of regular users of a recreational drug having symptoms of an organ disease is not a rare adverse event — it is a defining feature of the drug, and it went unrecognised for a generation because nobody was dying of it.

A poison is a drug whose kinetics have escaped its pharmacology.

The toxic principle

Ketamine is a non-competitive NMDA receptor antagonist, binding within the open channel pore rather than at the glutamate site. That mechanism is what it shares with nitrous oxide, with phencyclidine, and with the newer dissociatives such as methoxetamine — and it accounts for the dissociative state directly.

Two features of ketamine's pharmacology explain the rest of the acute picture. It is sympathomimetic — it inhibits catecholamine reuptake, so heart rate and blood pressure rise rather than fall, which is unique in this band among the CNS depressants and is the reason ketamine is used in shocked patients. And it is a bronchodilator, which follows from the same catecholamine effect.

The bladder — a real disease with an unresolved mechanism

Ketamine-associated uropathy is well established as a clinical entity: contracted bladders and other urinary tract abnormalities in ten young users³, with a dose and frequency relationship demonstrated in 1285 recent users.² What causes it is not settled. Direct urothelial toxicity from ketamine or its metabolites in urine, microvascular injury, an immune or inflammatory response and neurogenic mechanisms have all been proposed. The concentration argument — that the urothelium is exposed to concentrations far above those anywhere else in the body — is the most commonly offered explanation and is a reconstruction from the excretion route rather than a demonstration, and no cited source on this page identifies the responsible species. Inferred

This page therefore declines to name a toxic metabolite for the bladder, which is a departure from every other entry in the library — the toxic species field says so explicitly. Norketamine and further urinary metabolites are the usual candidates; the label states only that excretion is renal, mostly as conjugated metabolites¹, and offers nothing about urothelial effects at all, which is unsurprising for a document describing a single anaesthetic administration.

Toxicokinetics

The label's kinetics are those of a single anaesthetic dose in a hospital, which is a poor match for the recreational pattern — but the numbers still do useful work, particularly the distinction between the distribution half-life that ends the trip and the elimination half-life that does not.

Ketamine — an anaesthetic's kinetics, read for a recreational exposure¹
Parameter	Therapeutic	In overdose	Why it changes
Absorption	Rapidly absorbed following intramuscular administration¹. Insufflated recreationally, with effects within minutes; oral bioavailability is low because of extensive first pass	Redosing during a session produces a stepped exposure	The route determines the experience. Insufflation gives the recreational dissociation; the intramuscular and intravenous routes reach anaesthetic depth. Nothing here delays absorption, so a deteriorating patient is redosing rather than still absorbing.
Distribution	Rapidly distributed into perfused tissues including brain and placenta; highly concentrated in body fat, liver and lung in animal studies¹	Unchanged	Very rapid brain entry is what makes it an induction agent. The fat, liver and lung concentration is an animal finding on the label and is flagged as such.
Distribution half-life	The distribution phase lasts about 45 minutes, with a distribution half-life of 10 to 15 minutes, associated with an anaesthetic effect of about 20 minutes after a 2.5 mg/kg intravenous bolus¹	Unchanged	This is the number that governs the trip, not the elimination half-life. Consciousness returns because the drug leaves the brain for other tissues, exactly as for thiopental — redistribution ends the effect long before elimination ends the exposure.
Plasma concentrations	About 1.8 to 2.0 µg/mL at 5 minutes after an intravenous bolus of 2 mg/kg; about 1.7 to 2.2 µg/mL at 15 minutes after an intramuscular 6 mg/kg dose, in adults and children¹	—	Quoted because it shows how differently the two routes deliver: the intramuscular route needs three times the dose to reach a similar concentration ten minutes later. Recreational insufflation sits between the two.
Metabolism	Hepatic. CYP3A4 is the primary enzyme responsible for N-demethylation to norketamine, with CYP2B6 and CYP2C9 as minor contributors¹	Unchanged; CYP3A4 interactions are the theoretical concern	Norketamine is an active metabolite and is the usual candidate for the urothelial injury — but no source cited here demonstrates that, and the label says nothing about it. The single polymorphic-enzyme dependence that dominates the tramadol page is absent: three enzymes share the work.
Termination of effect	Partly by redistribution from brain to other tissues and partly by metabolism¹	Unchanged	The label states the redistribution mechanism explicitly, which is worth having in writing: it is the reason recovery from a single dose is much faster than the elimination half-life predicts.
Elimination half-life	Approximately 2 to 3 hours; excretion renal, mostly as conjugated metabolites¹	Unchanged	Renal excretion is the row that connects the acute pharmacology to the chronic disease. Metabolites are concentrated in urine and held against the urothelium — which is the basis of the concentration argument for the uropathy, and which this page marks as an inference rather than a finding.
Dialysability	—	Never assessed. EXTRIP has published no recommendation covering ketamine⁴	The absence is genuine and unimportant. The acute problem is a few hours of supported ventilation at most¹, and the chronic problem is structural bladder damage that removing drug from blood cannot touch.

Metabolism and the metabolites

Ketamine's metabolism is straightforward and is not, in itself, the interesting part. The interesting part is where the metabolites go, which is the urine, at concentrations no other tissue sees.

Ketamine — an unremarkable metabolism with one remarkable destination

KetamineAlready active. Non-competitive NMDA receptor antagonism at the open channel pore
Redistribution from brain to other tissuesConsciousness returnsDistribution half-life 10–15 minutes, matching an anaesthetic effect of about 20 minutes¹. This limb, not metabolism, ends the trip
CYP3A4 N-demethylation, with CYP2B6 and CYP2C9 minor¹NorketamineActive. The usual candidate for the bladder injury — not demonstrated by any source cited here
Conjugated metabolitesThe form in which most of the drug leaves¹
Urine, in contact with the urotheliumThe exposure that matters chronically. The concentration argument is an inference from this route, not a finding
Ulcerative cystitis and a contracted bladderContracted bladders in ten users³; urinary symptoms in 26.6% of 1285 recent users, dose- and frequency-related²

A frequency argument sits alongside the concentration one and is probably the stronger of the two. Winstock's survey found urinary symptoms significantly related to both dose of ketamine used and frequency of use², and it is the frequency term that distinguishes a recreational user from a patient given a single anaesthetic dose. A bladder exposed once recovers; a bladder exposed several times a week for years does not — which is why the disease belongs to recreational use and is essentially absent from anaesthetic practice.

Elimination and accumulation

Ketamine does not accumulate. Damage accumulates, which puts this page in the same category as nitrous oxide and outside the category of every pharmaceutical entry in the library.

What the survey data actually establish about the uropathy

Winstock and colleagues used purposeful sampling — an online questionnaire promoted by a national dance-music magazine and website between November 2009 and January 2010. 3806 surveys were completed; 1285 (33.8%) reported ketamine use within the last year; of those, 17% were dependent and 26.6% (340) reported urinary symptoms. Symptoms were significantly related to both dose and frequency. Of 251 users reporting their experience over time, 51% reported improvement on stopping, and only 8 (3.8%) reported deterioration after stopping.² That last figure is the hopeful one and it is also the limit of what the study can say — self-reported improvement in a self-selected online sample is not the same as demonstrated structural recovery.

The reversibility question is the one that matters most to a patient and is the one the evidence answers least well. Chu's ten cases had contracted bladders³ — a structural, fibrotic change that would not be expected to reverse — while Winstock's survey found symptomatic improvement in half of those who stopped.² Both can be true: symptoms improve early, and established fibrosis does not. The clinical implication is that the value of stopping is greatest before the bladder has contracted, which is precisely when the symptoms are mildest and the user least motivated.

Target organs — and why those

Bladder and upper urinary tract

TargetUrothelium, exposed to urinary rather than plasma concentrations

Why hereThe organ that makes ketamine a toxicology page rather than an anaesthesia one. Chu reported ten young users with contracted bladders and other urinary tract abnormalities, noting such findings had never previously been reported in ketamine abusers³; Winstock found urinary symptoms in 26.6% of 1285 recent users, related to both dose and frequency.² Why this organ is not established. The concentration-and-contact-time argument is the usual account and is inference from the renal excretion route¹; direct urothelial toxicity, microvascular injury and inflammatory mechanisms have all been proposed and none is demonstrated by any source cited here. Inferred

At the bedsideFrequency, urgency, dysuria, severe suprapubic pain, haematuria; in advanced disease a contracted, low-capacity bladder³, hydronephrosis and renal impairment. Ask about urinary symptoms in any ketamine user — they will not volunteer them, and 26.6% of regular users have them.²

Brain — NMDA receptors

TargetThe open channel pore of the NMDA receptor

Why hereThe acute effect, and the mechanism shared with nitrous oxide and with phencyclidine. Interrupting corticothalamic integration produces dissociation rather than sedation — a state with preserved reflexes and a subjective content, which is why the airway behaves so differently from the sedative-hypnotics. Established

At the bedsideDissociation, nystagmus, the 'K-hole' of profound detachment, emergence phenomena on recovery. Reassurance and a quiet environment are the conventional management; benzodiazepines are used for severe distress.

Respiratory system

TargetRespiratory drive at high dose; the airway indirectly

Why hereThe only acute hazard the label names: respiratory depression can result from an overdosage of ketamine hydrogenchloride. Supportive ventilation should be employed. Mechanical support of respiration ... is preferred to administration of analeptics.¹ The label's rejection of analeptics is worth noting — it is a document declining to recommend a stimulant antidote in favour of simply breathing for the patient. Hypersalivation and laryngospasm are separate airway risks that are not respiratory depression. Established

At the bedsideHypoventilation at high dose; laryngospasm, particularly with airway stimulation. The mechanism is the reason ketamine users obstruct less than GHB users — but 'less' is not 'never', and the label names the risk.

Cardiovascular system

TargetCatecholamine reuptake inhibition — a sympathomimetic effect

Why hereThe card that makes ketamine unique among the CNS depressants in this band. It raises heart rate and blood pressure rather than lowering them, which is why it is chosen as an induction agent in shock and why a ketamine presentation looks nothing like a GHB or benzodiazepine one at the bedside. The same effect produces bronchodilatation. Established

At the bedsideTachycardia and hypertension. A hypotensive, bradycardic dissociated patient has taken something else — the vital signs are a genuine discriminator here.

Liver and biliary tree

TargetNot established

Why hereA card included to mark an association rather than to explain one. Biliary tract abnormalities and deranged liver function are described in heavy chronic users, and are one candidate explanation for the abdominal pain those users report. No source cited on this page establishes the mechanism or the frequency, and this card exists because omitting it would imply the abdominal pain of a chronic user is always urological. Inferred

At the bedsideDeranged liver function tests and biliary dilatation in heavy chronic users. Worth investigating rather than attributing to the bladder by default.

Timeline of effects

Ketamine — an hour that resolves completely, and years that do not

Time

What you seeWhat is happening

0–5 minOnset
What you seeDissociation, nystagmus, ataxia, hypertension and tachycardia.
What is happeningRapid distribution into perfused tissue including brain¹. Plasma concentrations of about 1.8 to 2.0 µg/mL at five minutes after a 2 mg/kg intravenous bolus.¹
5–20 minPeak dissociation
What you seeThe 'K-hole' at higher doses — profound detachment with eyes open and reflexes preserved.
What is happeningNMDA receptor blockade at the open channel. Airway reflexes are relatively preserved, which is the mechanism's most useful clinical consequence.
20–60 minRecovery by redistribution
What you seeEmergence, sometimes with agitation or distressing perceptual phenomena.
What is happeningDistribution half-life 10 to 15 minutes, associated with an anaesthetic effect of about 20 minutes¹. The label states termination is partly by redistribution from brain to other tissues and partly by metabolism.¹ The drug has not left the body — it has left the brain.
Any pointThe acute hazard
What you seeRespiratory depression, and separately laryngospasm.
What is happeningThe only overdose effect the label names, managed by supportive ventilation in preference to analeptics.¹ Against this the label sets its wide margin: unintentional overdoses of up to ten times the usual dose followed by prolonged but complete recovery.¹
2–3 hElimination
What you seeFully recovered.
What is happeningElimination half-life approximately 2 to 3 hours, renal, mostly as conjugated metabolites.¹ The acute episode is over. The urothelial exposure has just happened.
Months to yearsThe bladder
What you seeThe gap drawn here is years of use with no acute event of any kind. Then frequency, urgency, dysuria and severe pain — often long after the user has stopped associating symptoms with the drug.
What is happeningRepeated urothelial exposure at urinary concentrations, related to both dose and frequency.² The mechanism is not established. Urinary symptoms in 26.6% of recent users²; contracted bladders in advanced disease.³
After stoppingPartial recovery
What you see51% of 251 users reported improvement on stopping; 3.8% reported deterioration.²
What is happeningSymptomatic improvement is well reported; structural change such as a contracted bladder³ would not be expected to reverse. The two findings are compatible and describe different stages of the same disease.

What the mechanism predicts at the bedside

Ask every ketamine user about urinary symptoms. Over a quarter of recent users have them² and they do not present them as drug-related.
Dissociation with tachycardia and hypertension is the pattern. A hypotensive, bradycardic patient has taken something else — ketamine is the sympathomimetic among this band's depressants.
Airway reflexes are relatively preserved but not guaranteed. The label names respiratory depression as the overdose effect and directs supportive ventilation.¹ Laryngospasm is a separate risk.
Acute recovery is by redistribution, not elimination — a distribution half-life of 10 to 15 minutes within a distribution phase of about 45 minutes¹ — so a patient still dissociated an hour later has redosed or taken something else.
The acute margin genuinely is wide, and the label says so¹. That is a reason to look hard for a co-ingestant when a ketamine patient is very unwell.
Severe abdominal or flank pain in a ketamine user is a presentation, not a side effect. Consider the bladder, the upper tracts and the biliary tree, and expect the patient to have been self-treating it with more ketamine.
A contracted bladder on imaging in a young person with no other explanation should prompt the question.³ The disease was described only in 2007 and is still under-recognised.
Stopping is worth more the earlier it happens. Half of users who stopped reported improvement², but fibrosis is not a symptom and does not reverse.
Analeptics are specifically not recommended — the label prefers mechanical support of respiration.¹
Dialysis has no role and has never been assessed⁴, and could not affect either the acute or the chronic problem.

The antidote, from the poison's side

There is no antidote, and the label does not want one. Its entire management advice for overdose is: supportive ventilation should be employed. Mechanical support of respiration that will maintain adequate blood oxygen saturation and carbon dioxide elimination is preferred to administration of analeptics.¹

Supportive ventilation: The treatment, and the only one the label names.¹ The acute problem is a few hours at most — elimination half-life 2 to 3 hours¹, with recovery from a single dose much faster because of redistribution.
Benzodiazepines: For distressing emergence phenomena and for agitation. Not an antidote — they treat the experience rather than the receptor blockade, and their sedation is additive to whatever respiratory depression is present.
Analeptics: Specifically not preferred, on the label's own wording.¹
Naloxone, flumazenil: No role. Ketamine acts at neither the opioid receptor nor the benzodiazepine site — mentioned only because a dissociated patient of unknown history will often have been given both.
Stopping the drug: The treatment for the disease, as opposed to the presentation. 51% of 251 users who reduced or stopped reported improvement in urinary symptoms; 3.8% reported deterioration.² It is the only intervention on this list that addresses what ketamine actually does to people.
Urological management: Necessary in established uropathy and outside this page's scope. Chu's cases had contracted bladders³, which is a structural problem requiring structural answers.
Extracorporeal removal: Never assessed⁴ and irrelevant to both the acute and the chronic problem.

Critical appraisal

The uropathy mechanism was badged traditional teaching and was downgraded to inferred at audit, and the two reviewers who examined it disagreed — so the reasoning is recorded in full. The badge rested on Chu's paper being a primary description of the disease that treats aetiology as an open question³. One reviewer argued that is a positive assertion of unknown-ness by the source that established the entity, structurally like the lithium precedent, and would have kept it with the sentence quoted verbatim. The other argued that Chu's abstract says only that the possible aetiology is also discussed — which signposts a discussion rather than contesting anything — and that the page's own justifications were worded as absences (no cited source identifies the responsible species), which the house rule refuses. The second argument was accepted, for two reasons: a signpost to a discussion is not a contest, and the identical claim already carried an inferred badge in the metabolism section of this same page, so the downgrade also removes an internal inconsistency. If Chu's full text positively asserts the aetiology is unknown, the badge can be restored on that quotation.
Winstock's survey is a purposeful, self-selected online sample.² 3806 surveys promoted by a dance-music magazine; 1285 reported ketamine use in the last year; 26.6% of those reported urinary symptoms. That 26.6% is a prevalence within a self-selecting group of recreational users at a particular time and place, and is not a population figure. Respondents with symptoms had an obvious reason to complete the survey. The dose–frequency relationship is the more robust finding, because internal comparisons within the sample are less vulnerable to that bias than the headline prevalence.
The 51% improvement figure comes from 251 users reporting their own experience over time², which is self-reported symptomatic change without objective assessment. It should not be read as evidence that the bladder recovers structurally, and this page separates the two claims explicitly.
Chu's series is ten patients from two hospitals in one city.³ It established that the entity exists; it establishes nothing about incidence, mechanism or prognosis, and no number from it is generalised here.
The 'up to 10 times' margin figure is the label's and is quoted exactly.¹ It refers to unintentional administration of anaesthetic overdoses in a clinical setting, which is not the same as a recreational overdose with unknown co-ingestants — and this page uses it to argue that a very unwell ketamine patient probably has a second problem, rather than to reassure.
The body-fat, liver and lung concentration finding is an animal one, and the label says so.¹ It is flagged in the kinetics table rather than described in human terms.
Norketamine is named as the usual candidate for the urothelial injury and is explicitly not asserted to be responsible. The label establishes only that CYP3A4 forms it and that excretion is renal, mostly as conjugated metabolites.¹ Naming a toxic metabolite that no source demonstrates would be exactly the kind of confident mechanism this library exists to badge, so the toxic-species field records the uncertainty instead.
The hepatobiliary card is the weakest on the page and is marked as inference. The association is described in the clinical literature; neither cited source addresses it, and no frequency is given.
No dose, threshold or lethality figure appears on this page. Recreational ketamine is of unknown purity and is increasingly sold interchangeably with other dissociatives such as methoxetamine.
EXTRIP has never addressed ketamine.⁴ The absence is uninformative — neither the acute nor the chronic problem is a drug-concentration problem.

References

1
Ketalar 50 mg/ml Injection (ketamine hydrochloride) — Summary of Product Characteristics. electronic medicines compendium, product 5202. Sections 4.9 (Overdose) and 5.2 (Pharmacokinetic properties). Source of the wide-margin statement and the ten-times-overdose observation, the 10–15 minute distribution half-life and 20-minute anaesthetic effect, the plasma concentrations by route, CYP3A4 N-demethylation to norketamine, the 2–3 hour elimination half-life and renal excretion mostly as conjugated metabolites, and the preference for mechanical support of respiration over analeptics. medicines.org.uk/emc/product/5202
2
Winstock AR, Mitcheson L, Gillatt DA, et al. The prevalence and natural history of urinary symptoms among recreational ketamine users. BJU International 2012 Dec;110(11):1762–6. PMID 22416998. doi:10.1111/j.1464-410X.2012.11028.x. (Purposeful online sampling promoted by a national dance-music magazine, November 2009 to January 2010; 3806 surveys completed, 1285 (33.8%) reported ketamine use within the last year, 17% of those dependent; 26.6% (340) reported urinary symptoms, significantly related to both dose and frequency; of 251 reporting experience over time, 51% reported improvement on cessation and 8 (3.8%) reported deterioration.)
3
Chu PS, Kwok SC, Lam KM, et al. 'Street ketamine'-associated bladder dysfunction: a report of ten cases. Hong Kong Medical Journal 2007 Aug;13(4):311–3. PMID 17592176. (Ten young ketamine users presenting to two regional hospitals with lower urinary tract symptoms; investigations demonstrated contracted bladders and other urinary tract abnormalities; states that these findings had never been reported before in ketamine abusers, and discusses possible aetiology as an open question.)
4
EXTRIP Workgroup — published recommendations index. Extracorporeal Treatments in Poisoning Workgroup. Cited for the absence of any recommendation covering ketamine. extrip-workgroup.org/recommendations

Ketamine

At a glance