Why this poison is interesting

Colchicine is the poison that punishes reassurance. It has a narrow therapeutic window and is extremely toxic in overdose,¹ and its course is biphasic: a gastrointestinal first phase that can look like a self-limiting gastroenteritis, a deceptive lull, and then — at 24 to 72 hours — multi-organ failure and marrow collapse.¹ The patient who is sent home because the vomiting has settled is the patient colchicine is most likely to kill.

It arrests cell division. Colchicine binds tubulin and prevents microtubule assembly, halting mitosis; the tissues that divide fastest — gastrointestinal epithelium and bone marrow — are hit first and hardest.¹² Established
So the damage is delayed and general. Antimitotic injury takes time to express itself as cells fail to be replaced, which is why the dangerous phase lags the ingestion and why, when it comes, it is multi-organ rather than confined to one system.¹
There is no antidote and no dialysis. Nothing reverses tubulin binding, and colchicine's very large volume of distribution — it is taken up into cells throughout the body — means haemodialysis cannot remove a meaningful fraction.¹ The treatment is supportive care and time.

Colchicine is the overdose that improves before it kills: the quiet interval is not recovery, it is incubation.

The toxic principle

There is one toxic principle — arrest of mitosis by tubulin binding — and the whole biphasic, multi-organ course follows from where and how fast cells divide.

Colchicine binds tubulin and blocks microtubule assembly. Microtubules are needed for the mitotic spindle, so cells cannot complete division; they are also needed for intracellular transport and for neutrophil motility, which is the basis of colchicine's anti-inflammatory use.¹² Established
The fastest-dividing tissues fail first. Gastrointestinal epithelium and bone marrow have the highest turnover, so the earliest and most prominent effects are gut (vomiting, diarrhoea, haemorrhagic gastroenteritis) and, later, marrow (pancytopenia).¹ Established
The injury is delayed because replacement is what fails. Cells are not killed instantly; they fail to be replaced as they normally would, so the clinical collapse appears over days as tissues that depend on constant renewal run down.¹ This is why the dangerous phase lags and why it is multi-organ.

Toxicokinetics

Colchicine — fast in, widely distributed, and slow to leave
Parameter	Therapeutic	In overdose	Why it changes
Absorption	Rapidly and almost completely absorbed; peak plasma concentration usually 30–120 minutes after ingestion¹	Rapid, so the drug reaches the tissues quickly even though the clinical effects are delayed	The gap between a fast absorption and a delayed illness is the whole trap: the drug is already in the cells long before the multi-organ phase appears, so an early normal examination reflects the lull, not the dose.
Protein binding	Approximately 30%¹	Unchanged — binding is modest and not the reason dialysis fails	Unusually, it is not protein binding that defeats the dialyser here (binding is only moderate) but the volume of distribution: most of the drug is inside cells, not free in plasma.
Volume of distribution	Very large — colchicine is taken up into cells throughout the body and accumulates in leucocytes¹	Unchanged and decisive — the large Vd is why haemodialysis has no efficacy¹	This is the key kinetic fact. A drug distributed overwhelmingly into cells presents only a tiny fraction to the blood at any moment, so an extracorporeal circuit cleaning the blood removes almost nothing. The label states plainly that haemodialysis has no efficacy because of the high apparent volume of distribution.
Metabolism	Partially metabolised in the liver and excreted in part via the bile¹	Hepatic impairment markedly reduces clearance (a cirrhotic patient showed a large fall in clearance)¹	The liver is a major route, so hepatic disease both prolongs exposure and identifies a higher-risk patient — one of the groups the label flags.
Elimination	Largely excreted in the faeces (about 80%) as unchanged drug and metabolites; 10–20% in the urine; terminal half-life about 3–10 hours, prolonged in renal impairment¹	Clearance falls with renal function — the terminal half-life lengthened roughly four-fold in severe renal impairment¹	Enterohepatic recycling and a partly renal exit mean both liver and kidney matter; in severe renal impairment the half-life was markedly prolonged, which is why impaired renal function is a named risk factor for a worse overdose.
Dialysability	—	Not dialysable — haemodialysis has no efficacy owing to the high apparent volume of distribution¹; EXTRIP has not assessed colchicine³	There is no extracorporeal rescue. Decontamination early (lavage, activated charcoal within an hour) is described by the label,¹ but once the drug is distributed the management is supportive organ support through the multi-organ phase.

Metabolism and the metabolites

Colchicine is partially metabolised by the liver and excreted largely in the bile and faeces, with a smaller renal component and pronounced uptake into cells — it accumulates in leucocytes.¹ There is no toxic metabolite driving the picture; the parent alkaloid is the poison, and metabolism and excretion matter chiefly because impairing them (liver or kidney disease) prolongs the tissue exposure.

Colchicine — a parent-drug poison with no rescuing exit

Colchicine (ingested)Toxic as the parent alkaloid — binds tubulin, arrests mitosis; accumulates in leucocytes¹²
Hepatic metabolism + biliary excretionFaecal elimination (~80%)The major route, with enterohepatic recycling; reduced by hepatic impairment¹
Renal excretion (10–20%)Urinary eliminationMinor route; clearance falls and half-life lengthens in renal impairment¹
Uptake into cells (large Vd)Intracellular colchicineWhere the drug mostly is — and why dialysis removes almost nothing¹

What changes the answer

Renal impairment — prolongs exposure and is a named risk factor for a worse outcome.¹ Established
Hepatic impairment — reduces the major clearance route and raises risk.¹ Established
Extremes of age — flagged by the label as higher-risk groups.¹
Co-administered inhibitors of colchicine's metabolism and transport can raise levels even without an overdose, a recognised cause of inadvertent toxicity. Inferred

Elimination and accumulation

Colchicine leaves the body slowly and by routes that both liver and kidney disease impair, and while it is present it sits mostly inside cells rather than in the blood. That combination — slow clearance, large intracellular reservoir — is why there is no way to accelerate its removal and why the illness must largely be waited out under organ support.

The EXTRIP position

EXTRIP has not assessed colchicine — it is absent from the workgroup's list of reviewed poisons.³ The absence is coherent: the label already states that haemodialysis has no efficacy because of the very large apparent volume of distribution,¹ so there is no extracorporeal question for the workgroup to answer.

Removal is not possible once distributed — the large volume of distribution keeps the drug out of reach of the dialyser.¹
Decontamination is the only removal step, and only early: the label describes gastric lavage within an hour and activated charcoal within an hour of presentation.¹
The rest is organ support through the second phase — marrow failure, renal failure, myocardial depression and coagulopathy are managed as they arise, because the drug cannot be taken out and there is nothing to give that reverses it.¹

Target organs — and why those

Gastrointestinal tract

TargetThe rapidly-dividing gut epithelium

Why hereThe gut lining has one of the body's highest turnover rates, so an antimitotic poison strikes it first.¹² Established

At the bedsideNausea, vomiting, abdominal pain, diarrhoea and haemorrhagic gastroenteritis in the first phase, with volume depletion and electrolyte disturbance.¹ This is the phase that can be mistaken for gastroenteritis and that precedes the lull.

Bone marrow

TargetHaematopoietic stem and progenitor cells

Why hereThe marrow divides constantly to replace blood cells, so it fails as division is arrested — the classic late sign.¹² Established

At the bedsidePancytopenia in the second phase, with the neutropenia exposing the patient to sepsis — a major cause of death. Recovery, if it comes, may be heralded by a rebound leukocytosis about a week after ingestion.¹

Heart

TargetMyocardial cellular function

Why hereMicrotubule disruption and the systemic insult of the second phase depress myocardial function and provoke dysrhythmias.¹ Inferred

At the bedsideMyocardial depression, hypotension progressing to cardiogenic shock, and dysrhythmias in severe poisoning; cardiovascular collapse is a usual mode of death.¹

Kidney

TargetRenal tubular and glomerular function

Why hereAcute renal failure is part of the multi-organ second phase, compounded by volume depletion and shock; impaired renal clearance in turn prolongs the colchicine exposure.¹ Inferred

At the bedsideAcute kidney injury in the 24–72 hour window, both a consequence of the poisoning and a factor worsening it.

Peripheral nerves

TargetAxonal microtubule-dependent transport

Why hereMicrotubules carry out axonal transport, so their disruption produces a peripheral neuropathy.¹ Inferred

At the bedsideAn ascending peripheral motor and sensory neuropathy described in the second phase.¹ Reversible alopecia, another marker of antimitotic injury to a high-turnover tissue, can appear around a week out.¹

Timeline of effects

Colchicine's timeline is the textbook deceptive course: a gastrointestinal opening, a misleading lull, and then a multi-organ collapse at 24–72 hours. The danger is concentrated in the interval when the patient appears to be recovering.

Colchicine — GI first, a lull, then multi-organ failure

Time

What you seeWhat is happening

0–24 hGastrointestinal phase
What you seeNausea, vomiting, abdominal pain, diarrhoea and haemorrhagic gastroenteritis, with volume depletion, electrolyte abnormalities, a leukocytosis and, in severe cases, hypotension. Symptoms may be delayed, on average around three hours.¹
What is happeningAntimitotic injury to the fast-dividing gut epithelium, and the systemic effects of fluid and electrolyte loss.¹² The drug is already absorbed and distributed; the decontamination window is early and narrow.
24–72 hMulti-organ failure
What you seeThe life-threatening phase: multisystem organ dysfunction — acute renal failure, confusion and coma, ascending peripheral neuropathy, myocardial depression, pancytopenia, dysrhythmias, respiratory failure and a consumption coagulopathy. Death is usually from respiratory depression and cardiovascular collapse.¹
What is happeningThe antimitotic injury of the first hours now expresses itself as the fastest-dividing tissues fail to renew — marrow and gut above all — with microtubule disruption and the systemic insult depressing the heart, kidneys and nerves.¹² This is the genuine latent phase: the collapse arrives after a gastrointestinal picture that can appear to settle, which is the poison's signature deception.
About 1 week onwardRecovery (if it comes)
What you seeIn survivors, recovery may be accompanied by a rebound leukocytosis and reversible alopecia starting about a week after ingestion.¹
What is happeningAs the drug is finally cleared, the arrested tissues resume division; the rebound leukocytosis and the hair loss are both markers of high-turnover tissues recovering from, or still registering, the antimitotic hit.¹

What the mechanism predicts at the bedside

Why the first phase is deceptive

Because the injury is antimitotic, it expresses itself as a failure of cell replacement over days, not as immediate cell death.¹² So the gastrointestinal opening can settle while the marrow and other tissues are already committed to failing, and the improving patient at 18 hours is in the lull, not in recovery. The mechanism is the reason the course is biphasic and the reason early reassurance is unsafe. Established

Why there is no antidote and no dialysis

Tubulin binding cannot be reversed by any available agent, and colchicine's very large volume of distribution keeps it inside cells and away from the dialyser, which the label states has no efficacy.¹ So neither of the two usual specific levers — an antidote or extracorporeal removal — is available, and the management is early decontamination plus organ support through the second phase.

Why the patient's liver and kidney change the risk

Colchicine is cleared by both biliary/faecal and renal routes, and impairment of either prolongs the exposure of the dividing tissues;¹ renal impairment lengthened the terminal half-life markedly.¹ This is why the label singles out renal and hepatic impairment and the extremes of age as higher-risk, and why those patients warrant particular caution. Established

Why survival is about supporting organs, not clearing drug

With no way to remove or reverse the drug, survival depends on carrying the patient through the 24–72 hour multi-organ phase — neutropenic sepsis precautions, haemodynamic support, renal support, transfusion and correction of coagulopathy.¹ The rebound leukocytosis at about a week is the biological signal that the arrested marrow is recovering.

The antidote, from the poison's side

Colchicine has no antidote, and the reason is structural: the poison interferes directly with a protein every dividing cell needs, which offers nothing for an antidote to act on. This section describes what stands in an antidote's place — early decontamination and organ support — and why the mechanism leaves no better option.

No agent reverses tubulin binding. There is nothing to give that neutralises colchicine at its site of action, so the search for a pharmacological antidote is futile.¹ Established
Early decontamination is the only removal — gastric lavage and activated charcoal within an hour, while the drug is still in the gut; once distributed it cannot be retrieved.¹
Dialysis does not work because the drug is intracellular and the volume of distribution is huge.¹ There is no extracorporeal fallback of the kind metformin has.
Organ support is the definitive care — anticipating and treating the marrow, cardiac, renal and coagulation failure of the second phase, and carrying the patient to the recovery heralded by the rebound leukocytosis.¹

Critical appraisal

The antimitotic, tubulin-binding mechanism is well established and clinically load-bearing.¹² It explains the biphasic course, the multi-organ pattern, the marrow and gut prominence, and the absence of an antidote. It is the firmest element on the page.
The biphasic timeline is the page's central safety message and is taken directly from the label.¹ The 24–72 hour window for the multi-organ phase and the instruction to refer every overdose are explicit, and the page's repeated warning about the lull is a faithful amplification of that instruction rather than an independent claim.
The no-dialysis conclusion is stated by the label and mechanistically sound.¹ A very large volume of distribution defeats extracorporeal removal regardless of the modest protein binding, and the page is careful to attribute the failure to the volume of distribution, not the binding — a distinction that matters because it is the opposite of the salicylate/valproate story.
The organ-level mechanisms beyond gut and marrow are reasonably inferred, not individually cited. Inferred Myocardial depression, acute renal failure and the neuropathy are listed by the label as second-phase features;¹ attributing each specifically to microtubule disruption is a coherent extension of the one mechanism rather than a separately evidenced claim, and the page badges them accordingly.
Lethal-dose figures were deliberately withheld. The label prints a lethal range; this page does not, consistent with the library's editorial boundary, and routes the quantities to TOXBASE and NPIS.
EXTRIP's silence is argued, not assumed.³ The label's explicit statement that haemodialysis has no efficacy makes an extracorporeal review moot, so the workgroup's not having assessed colchicine is coherent rather than a gap.

References

1
Colchicine 500 micrograms Tablets — Summary of Product Characteristics. emc product 6415. §4.9 and §5.2 fetched and read in full. Source of the narrow therapeutic window and extreme toxicity in overdose, the named higher-risk groups (renal or hepatic impairment, gastrointestinal or cardiac disease, extremes of age), the instruction to refer all overdoses even if asymptomatic, the average three-hour delay to symptoms, the biphasic course with the 24–72 hour multi-organ phase and its named features, death usually from respiratory depression and cardiovascular collapse, the rebound leukocytosis and reversible alopecia at about a week, the statement that no antidote is available, the statement that haemodialysis has no efficacy because of the high apparent volume of distribution, the decontamination measures, and the pharmacokinetics (30–120 min peak, 3–10 h half-life, ~30% protein binding, leucocyte accumulation, ~80% faecal and 10–20% urinary excretion, and the prolonged half-life and reduced clearance in renal and hepatic impairment). Lethal-dose figures in the label were deliberately not reproduced. Verified 13 Sep 2026.
2
Standard pharmacology of colchicine — binding to tubulin and inhibition of microtubule assembly, arresting mitosis and impairing microtubule-dependent processes including neutrophil function. Uncontested textbook mechanism, stated here without a dedicated primary citation in the manner the library applies to established pharmacology; the clinical consequences are anchored to the SmPC ¹. Flagged in the critical appraisal.
3
EXTRIP Workgroup — recommendations index. extrip-workgroup.org/recommendations. Consulted 13 Sep 2026 to confirm that colchicine is not among the poisons the workgroup has assessed — it does not appear on the published list of reviewed agents. Cited here for that absence, which is coherent with the label's statement that haemodialysis has no efficacy.
4
TOXBASE — colchicine. National Poisons Information Service. toxbase.org (NHS login required. NPIS: 0344 892 0111. The authoritative UK source for risk stratification, decontamination decisions, monitoring and organ support. Login-gated, so not quoted here.)

Colchicine

At a glance