Toxicology – Colchicine

Core Concept

Colchicine is a potent microtubule-disrupting alkaloid with a narrow therapeutic index. Severe poisoning is characterized by an initially gastrointestinal illness followed by rapidly progressive multiorgan failure, cardiovascular collapse, bone-marrow suppression, respiratory failure, coagulopathy, and sepsis.

A useful toxicologic sequence is:

Colchicine → tubulin binding → failure of microtubule polymerization → impaired mitosis and intracellular transport → GI mucosal injury + myocardial dysfunction + bone-marrow suppression + multiorgan failure

The typical clinical progression is triphasic: severe gastroenteritis during the first day, systemic organ failure over the next several days, and—if the patient survives—marrow recovery, rebound leukocytosis, and alopecia after approximately one week.

There is currently no commercially available specific antidote. Treatment requires early recognition, gastrointestinal decontamination when appropriate, aggressive intensive supportive care, and serial surveillance for delayed marrow failure.

Current Forms and Uses

Modern colchicine is principally administered orally. U.S. formulations include 0.6-mg tablets and capsules, while the cardiovascular product LODOCO contains 0.5 mg. Current indications include treatment and prophylaxis of gout flares and familial Mediterranean fever. Colchicine also has specialist uses in inflammatory diseases and pericarditis, while low-dose colchicine 0.5 mg daily is now approved in the United States to reduce cardiovascular events in adults with established atherosclerotic disease or multiple cardiovascular risk factors.

The historical practice of treating acute gout with 0.6 mg every hour until diarrhea or a cumulative 6 mg is obsolete and dangerous. The current FDA-labeled regimen for an acute gout flare is 1.2 mg initially followed by 0.6 mg one hour later, for a total of 1.8 mg, because higher doses provide no additional efficacy and substantially increase adverse effects.

Intravenous colchicine should also be regarded as historical in the United States. FDA took enforcement action in February 2008 to remove unapproved injectable colchicine products from the market because of the drug’s narrow therapeutic margin and the danger of fatal dosing errors with intravenous administration.

Plant Sources

Colchicine occurs naturally in Colchicum autumnale, commonly called autumn crocus or meadow saffron, and in Gloriosa superba, commonly called glory lily or flame lily. All portions of these plants can be toxic. Gloriosa tubers and seeds contain substantial amounts of colchicine and related alkaloids, while accidental Colchicum autumnale poisoning has occurred when leaves are mistaken for edible wild plants such as wild garlic.

Plant poisoning can be every bit as severe as pharmaceutical colchicine poisoning. A large Sri Lankan series of Gloriosa superba self-poisoning reported approximately 10% mortality, demonstrating that the older claim that plant intoxication is usually less severe is incorrect.

Mechanism of Toxicity

Colchicine binds to tubulin and prevents normal polymerization of microtubules. Because microtubules are necessary for mitosis, vesicular transport, maintenance of cellular structure, leukocyte movement, and many other cellular processes, colchicine toxicity affects far more than simply cell division.

Rapidly proliferating tissues are particularly vulnerable, including the gastrointestinal epithelium, bone marrow, and hair follicles, explaining the characteristic progression from gastroenteritis to pancytopenia and later alopecia. Myocardial and neuromuscular tissues can also be severely affected because microtubule disruption interferes with cellular transport, electrophysiology, contractility, and energy metabolism.

Pharmacokinetics

Colchicine is absorbed relatively rapidly after oral ingestion, with peak concentrations after ordinary therapeutic doses occurring at approximately one hour. It undergoes significant hepatic metabolism and biliary excretion, as well as renal elimination. It is a substrate for both CYP3A4 and P-glycoprotein (P-gp) and undergoes enterohepatic recirculation.

These characteristics help explain why toxicity may be prolonged and why drug interactions are so important. Colchicine also has extensive tissue distribution, which is one reason extracorporeal removal is ineffective once systemic absorption has occurred.

Drug Interactions

Modern understanding of colchicine interactions is substantially different from the older emphasis on cimetidine and tolbutamide. The most important interactions involve inhibitors of:

CYP3A4 and P-glycoprotein

Important examples include clarithromycin, erythromycin, azole antifungals, cyclosporine, several HIV protease inhibitors, and other strong CYP3A4/P-gp inhibitors. These drugs can markedly increase colchicine exposure and have produced life-threatening or fatal toxicity even when colchicine itself was prescribed at therapeutic doses.

The combination is particularly dangerous in patients with renal or hepatic impairment. Current colchicine labeling contraindicates coadministration of strong CYP3A4 or P-gp inhibitors with colchicine in patients with renal or hepatic impairment because fatal interactions have occurred.

FDA’s review of historical colchicine deaths found that a substantial proportion of non-overdose fatalities involved drug interactions, with clarithromycin especially prominent.

Statins and Myotoxicity

Colchicine can itself cause neuromyopathy and rhabdomyolysis, particularly when accumulation occurs. Concomitant statins, fibrates, cyclosporine, and other myotoxic medications can increase this risk. Current labeling reports myopathy and rhabdomyolysis—including fatal cases—with colchicine and HMG-CoA reductase inhibitors.

Therefore, weakness or muscle pain in a patient receiving colchicine should not automatically be attributed to gout, age, or deconditioning.

Renal and Hepatic Impairment

Renal and hepatic dysfunction both increase the risk of colchicine accumulation and toxicity. Current dosing must be modified according to renal function, hepatic function, indication, and concomitant interacting medications. Severe renal impairment requires markedly reduced prophylactic dosing and prolonged intervals between treatment courses.

The important toxicology principle is that:

Therapeutic dosing can become toxic when clearance is impaired.

Therefore a patient can have severe colchicine poisoning without a deliberate overdose.

Toxic Dose

Colchicine has a notoriously narrow therapeutic margin. Historically, oral exposures have been divided into approximate risk categories of <0.5 mg/kg, 0.5–0.8 mg/kg, and >0.8 mg/kg. Early reports suggested little mortality below 0.5 mg/kg, significant toxicity between 0.5 and 0.8 mg/kg, and near-universal mortality above 0.8 mg/kg.

These categories remain useful as rough risk markers but should not be treated as reliable outcome thresholds. Modern case reports document critical illness after doses well below 0.5 mg/kg, including severe multiorgan poisoning after approximately 0.2 mg/kg, while survival has occurred after doses historically classified as lethal.

Thus:

There is no absolute “safe” or inevitably fatal colchicine dose.

Any substantial overdose deserves aggressive assessment, and symptoms matter more than a historical dose cutoff.

Clinical Course

Colchicine poisoning is classically divided into three overlapping phases. This triphasic description is useful clinically but should not be interpreted as an exact timetable.

Phase 1 – Gastrointestinal Toxicity

The first phase usually develops within the first several hours and predominates during approximately the first 24 hours. Patients develop nausea, profuse vomiting, severe abdominal pain, and watery diarrhea, sometimes with gastrointestinal bleeding.

The syndrome can resemble severe gastroenteritis or cholera and may cause profound volume depletion, electrolyte abnormalities, metabolic acidosis, and early hypotension. Leukocytosis is common during this stage.

Importantly, the gastrointestinal symptoms are not simply benign adverse effects. In a significant overdose they represent direct gastrointestinal cellular injury and can be the first warning of impending systemic toxicity.

Phase 2 – Multiorgan Failure

The second phase typically becomes apparent after approximately 24 hours and may continue for several days. This is the life-threatening phase, characterized by progressive dysfunction of the cardiovascular, hematologic, respiratory, hepatic, renal, neurologic, and muscular systems.

Patients may develop shock, myocardial depression, ventricular dysrhythmias, ARDS, renal and hepatic injury, disseminated intravascular coagulation, encephalopathy, seizures, rhabdomyolysis, and profound bone-marrow suppression. Death during this phase is commonly caused by cardiovascular collapse, respiratory failure, or progressive multiorgan failure.

Phase 3 – Recovery

Patients who survive the period of multiorgan dysfunction generally enter a recovery phase beginning around day 7 or later. Bone marrow activity returns, often producing rebound leukocytosis, and alopecia may appear as damaged hair follicles enter recovery.

Weakness, neuropathy, and myopathy may persist for weeks, but survivors can eventually make a substantial or complete recovery if irreversible hypoxic or organ injury has not occurred.

Gastrointestinal Toxicity

Nausea, vomiting, abdominal cramping, and diarrhea are usually the earliest symptoms. Severe fluid losses can produce hypovolemic shock, renal hypoperfusion, metabolic acidosis, and major electrolyte abnormalities.

The onset of diarrhea after therapeutic colchicine is also an important warning sign. Because gastrointestinal effects are dose-related, new significant diarrhea in a patient receiving colchicine—particularly with renal disease or interacting medications—should trigger immediate review of dosing and toxicity risk.

Cardiovascular Toxicity

Cardiovascular failure is one of the most important causes of early death. Colchicine can produce myocardial dysfunction, reduced contractility, conduction abnormalities, dysrhythmias, and refractory shock. Patients may initially be tachycardic from dehydration and physiologic stress but later develop severe pump failure and vasoplegia.

ECG abnormalities can include conduction disturbances and nonspecific ST-T changes. Troponin elevation may occur with myocardial injury. Bedside echocardiography is particularly useful in severe poisoning to distinguish hypovolemia, vasodilatory shock, and cardiogenic myocardial depression.

Pulmonary Toxicity

Severe poisoning may progress to acute respiratory failure and ARDS. Respiratory failure can reflect pulmonary edema, systemic inflammation, neuromuscular weakness, aspiration, cardiovascular collapse, or a combination of these processes.

Patients with increasing oxygen requirements, altered consciousness, or progressive shock require early critical-care involvement and may need lung-protective mechanical ventilation.

Hematologic Toxicity

A characteristic feature of significant colchicine poisoning is delayed bone-marrow suppression. Early leukocytosis may be followed by leukopenia, neutropenia, thrombocytopenia, anemia, and potentially pancytopenia or aplastic marrow failure.

The nadir commonly occurs around days 3–7, although the exact timing varies. Current labeling recognizes leukopenia, granulocytopenia, thrombocytopenia, pancytopenia, and aplastic anemia as manifestations of colchicine toxicity.

Severe poisoning may also produce disseminated intravascular coagulation and bleeding.

Neutropenic Sepsis

Once severe neutropenia develops, secondary bacterial or fungal infection can become life-threatening. Fever during this stage must never simply be attributed to colchicine toxicity.

Fever + severe neutropenia = treat as febrile neutropenia/sepsis until proven otherwise.

Broad-spectrum antimicrobial therapy should be initiated promptly according to contemporary febrile-neutropenia protocols after appropriate cultures, without delaying treatment for microbiologic confirmation.

G-CSF

Granulocyte colony-stimulating factor, such as filgrastim, has been used in severe colchicine-induced neutropenia and marrow suppression. Published case series report accelerated recovery of neutrophil counts, but controlled outcome evidence is limited.

Therefore G-CSF is reasonable to consider in severe poisoning with substantial neutropenia, particularly febrile neutropenia, after hematology/toxicology consultation. It should be considered an adjunct rather than a colchicine antidote.

Hepatic Toxicity

Significant colchicine poisoning can produce hepatocellular injury with rising aminotransferases, bilirubin abnormalities, and impaired synthetic function. Prolonged INR may reflect both hepatic injury and disseminated intravascular coagulation.

Severe hepatic dysfunction generally occurs in the setting of broader multiorgan poisoning rather than isolated liver toxicity.

Renal Toxicity

Acute kidney injury may result from several mechanisms including severe dehydration, shock, rhabdomyolysis, multiorgan failure, and direct cellular toxicity. Urinalysis may reveal hematuria, proteinuria, or myoglobinuria.

Renal failure is particularly important because impaired colchicine clearance can further prolong systemic exposure.

Muscular and Neurologic Toxicity

Colchicine can produce myopathy, rhabdomyolysis, peripheral neuropathy, weakness, and hyporeflexia. Neuromuscular toxicity is particularly recognized during chronic therapeutic accumulation in patients with renal impairment or interacting medications, but it can also occur during major acute poisoning.

Severe acute poisoning may produce confusion, delirium, seizures, coma, and profound weakness. Neurologic abnormalities should also trigger evaluation for hypoxia, electrolyte disturbances, hypoglycemia, sepsis, and other causes.

Alopecia

Hair loss is a classic delayed finding and usually becomes apparent about one to several weeks after substantial poisoning. It reflects interruption of mitosis in rapidly dividing hair-follicle cells and is typically reversible in survivors.

Alopecia appearing during recovery can therefore retrospectively strengthen the diagnosis of significant colchicine exposure.

Diagnosis

Diagnosis is usually clinical and is based on known or suspected exposure combined with the characteristic progression from gastroenteritis to multiorgan dysfunction and marrow suppression.

Important clues include access to colchicine medication, treatment for gout or FMF, recent prescription of a CYP3A4/P-gp inhibitor, renal impairment, or ingestion of Colchicum autumnale or Gloriosa superba.

The differential includes iron poisoning, salicylate poisoning, arsenic, organophosphate or carbamate poisoning, toxic mushrooms or plants, severe infectious gastroenteritis, sepsis, and other cytotoxic or antimitotic agents.

Laboratory Evaluation

All significant exposures require serial laboratory testing rather than a single reassuring initial panel. Appropriate studies include CBC with differential and platelets, electrolytes, bicarbonate, glucose, BUN, creatinine, magnesium, calcium, liver enzymes, bilirubin, PT/INR, aPTT, fibrinogen, CK, lactate, and urinalysis.

Severe poisoning warrants blood-gas analysis, type and crossmatch, serial coagulation studies, and frequent assessment for hypoglycemia, acidosis, rhabdomyolysis, hepatic failure, and evolving marrow suppression.

The CBC is especially important because the initial leukocytosis can create false reassurance before a later precipitous decline in leukocytes and platelets.

ECG and Cardiac Assessment

An ECG and continuous cardiac monitoring are appropriate for significant poisoning. Serial ECGs should be obtained when hemodynamic instability or conduction abnormalities develop.

In severe shock, cardiac biomarkers and bedside echocardiography can help identify myocardial dysfunction. Persistent or worsening cardiogenic shock despite conventional treatment should prompt early discussion with a center capable of advanced mechanical circulatory support.

Colchicine Concentrations

The old statement that colchicine concentrations are completely useless requires nuance. Specialized quantitative colchicine testing is not routinely available rapidly enough to guide emergency management and there is no widely validated therapeutic decision threshold, so initial treatment should never wait for a level.

However, research involving Gloriosa superba poisoning found that admission plasma colchicine concentrations correlated strongly with mortality. Thus, concentrations can have toxicokinetic or prognostic value in specialized settings even though they remain impractical for routine bedside management.

Initial Treatment

Any significant colchicine overdose should be discussed early with a poison center or medical toxicologist. Patients with substantial intentional ingestion, severe gastrointestinal symptoms, hemodynamic abnormalities, laboratory abnormalities, or uncertain high-risk doses require hospital admission, usually to a high-acuity monitored setting.

The patient can initially look relatively well while irreversible intracellular toxicity is developing. Early aggressive care is therefore preferable to waiting for overt multiorgan failure.

Airway and Breathing

Airway management should follow standard critical-care principles. Intubation is appropriate for coma, respiratory failure, severe aspiration risk, or progressive shock with inability to maintain adequate ventilation.

ARDS should be managed with lung-protective ventilation and appropriate PEEP.

Circulation and Shock

Early shock may reflect profound gastrointestinal fluid loss, and isotonic crystalloid should be administered when hypovolemia is present. Severe cases often progress to mixed distributive and cardiogenic shock, so further fluids should be guided by examination, ultrasound, hemodynamics, and response rather than indiscriminate large-volume administration.

Persistent shock generally requires norepinephrine, with additional vasoactive or inotropic support individualized to cardiac function. Echocardiography can help identify severe myocardial depression.

Rare patients with otherwise refractory cardiogenic or mixed shock have been managed with extracorporeal life support. This remains rescue therapy for selected catastrophic cases rather than routine treatment.

Gastrointestinal Decontamination

Induced Emesis

Do not induce vomiting and do not use ipecac.

The old recommendation to induce emesis within 30 minutes is obsolete. These patients frequently vomit spontaneously, can deteriorate rapidly, and are at risk for aspiration.

Activated Charcoal

Colchicine is adsorbed by activated charcoal, so single-dose activated charcoal should be considered after a recent potentially serious oral ingestion when the airway is intact or protected. The greatest expected benefit is early after ingestion. Routine charcoal in every patient is not supported, and it is contraindicated when the airway is unprotected.

Because colchicine undergoes enterohepatic recirculation, multiple-dose activated charcoal (MDAC) has a plausible pharmacokinetic rationale and is sometimes used after severe poisoning. However, controlled evidence that MDAC reduces mortality is lacking, and general toxicology guidelines have not established colchicine as one of the classic evidence-supported MDAC indications.

Thus MDAC should be viewed as a specialist-directed adjunct in major poisoning, provided bowel function and airway safety permit it.

Gastric Lavage

Several older colchicine reviews and even some current product labels continue to recommend gastric lavage after severe recent ingestion. However, modern toxicology position statements conclude that gastric lavage should not be performed routinely, if at all, because clinical benefit is unproven and serious complications can occur.

Only an extraordinary, immediately life-threatening, very recent ingestion could justify lavage after airway protection and consultation with an experienced medical toxicologist. It should not be a routine response to colchicine overdose.

Antidote

There is currently no commercially available specific antidote for colchicine poisoning.

Supportive critical care remains the standard treatment.

Colchicine-Specific Fab Fragments

Colchicine-specific antibody Fab fragments represent a genuine potential antidotal strategy. A landmark human case described dramatic improvement after administration of colchicine-specific Fab in a patient with otherwise extremely severe poisoning.

Animal models also demonstrate effective binding and redistribution of colchicine. However:

Colchicine-specific Fab fragments are not commercially available for routine clinical use.

They should therefore be regarded as an experimental antidote rather than something an emergency department can ordinarily obtain. Contemporary reviews continue to identify Fab development as an important future therapeutic strategy.

Hemodialysis

Hemodialysis does not effectively remove colchicine.

Colchicine has extensive tissue distribution and rapidly leaves the vascular compartment. Current prescribing information specifically states that colchicine is not effectively removed by dialysis.

Therefore dialysis should not be initiated simply to enhance colchicine elimination.

It remains appropriate for conventional indications such as refractory hyperkalemia, severe metabolic acidosis, volume overload, or severe kidney failure. In such situations dialysis is treating the complications of poisoning rather than substantially clearing colchicine.

Hemoperfusion, Plasma Exchange, and Other Extracorporeal Techniques

Hemoperfusion, plasma exchange, hemofiltration, and related extracorporeal approaches have been reported in severe cases, but evidence is limited to case reports and small series. Because colchicine rapidly distributes into tissues, these methods are not established antidotal treatments.

They may sometimes be used as part of multiorgan supportive care or experimental rescue strategies, but clinicians should not expect reliable toxin clearance.

Rhabdomyolysis

Rhabdomyolysis should be treated with adequate IV crystalloid, correction of electrolyte abnormalities, and management of the underlying shock or hyperthermia. Serial CK, potassium, calcium, creatinine, and urine output should be monitored.

Routine urine alkalinization is not an established colchicine treatment.

Coagulopathy and Bleeding

Severe disseminated intravascular coagulation may require blood-product support according to bleeding, fibrinogen concentration, platelet count, and coagulation status. Packed red blood cells, platelets, cryoprecipitate, and plasma should be used according to standard critical-care/transfusion indications rather than prophylactically solely because colchicine was ingested.

Infection Management

The risk of infection rises substantially when neutropenia develops. Cultures should be obtained when infection is suspected, but broad-spectrum antibiotics should not be delayed in a hemodynamically unstable or febrile neutropenic patient.

Routine prophylactic antibiotics for every early colchicine ingestion are not established. Therapy should be driven by neutropenia, fever, documented infection, or standard ICU infectious indications.

Plant Poisoning Management

Poisoning from Colchicum autumnale or Gloriosa superba should be managed according to the same principles as pharmaceutical colchicine poisoning. Do not assume a natural product is milder.

When plant material is available, preserve it for botanical identification. Accidental Colchicum autumnale ingestion can occur when leaves are mistaken for wild garlic or other edible plants, while Gloriosa superba tuber ingestion may be intentional in regions where the plant is readily available.

Pregnancy

The old FDA Pregnancy Category D system is obsolete, and the statement that therapeutic colchicine is associated with Down syndrome or “trisomy 23” should not be carried forward.

Current labeling states that decades of published human experience with therapeutic colchicine during pregnancy have not identified an increased risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes, although colchicine crosses the placenta and animal studies demonstrate developmental toxicity at sufficient exposures.

In acute overdose, maternal resuscitation and treatment of shock, hypoxemia, multiorgan failure, and electrolyte abnormalities take priority.

Breastfeeding

The old implication that breastfeeding should generally be avoided is also outdated for therapeutic colchicine use. Colchicine enters breast milk, but LactMed reports that maternal doses up to approximately 1.5 mg/day result in an infant exposure below 10% of the maternal weight-adjusted dose, and published studies have not identified adverse effects in breastfed infants. Many expert guidelines consider therapeutic colchicine compatible with breastfeeding.

This therapeutic evidence should not be extrapolated to a mother with acute colchicine overdose. Breastfeeding decisions during significant maternal poisoning require individualized toxicology and pediatric assessment.

Observation

A known significant overdose should not be discharged after a short symptom-free interval simply because the patient initially appears well. Gastrointestinal manifestations may be delayed for several hours and systemic deterioration can become evident during the following day.

The older 24-hour asymptomatic observation rule is safer than a short ED observation period but should still be individualized. Because of the potentially catastrophic delayed course, deliberate or uncertain substantial ingestions generally warrant prolonged observation with serial laboratory testing and toxicology consultation.

Admission

Hospital admission is appropriate for any patient with significant intentional overdose, substantial plant ingestion, gastrointestinal symptoms, metabolic abnormalities, cardiovascular abnormalities, renal or hepatic dysfunction, or an uncertain potentially serious dose.

ICU admission is appropriate for severe vomiting/diarrhea with major fluid loss, hypotension, metabolic acidosis, myocardial dysfunction, dysrhythmia, respiratory failure, significant coagulopathy, evolving multiorgan failure, or severe neurologic toxicity.

Monitoring

Patients with serious poisoning require continuous cardiac and respiratory monitoring together with frequent assessment of hemodynamics and urine output. Serial CBC with differential, platelet count, electrolytes, renal function, liver function, coagulation studies, lactate, CK, and acid-base status are essential.

Importantly, monitoring must continue after the gastrointestinal symptoms improve because marrow suppression often worsens after the patient appears to be recovering from the initial GI illness.

Prognosis

Prognosis depends on dose, timing of treatment, age, renal and hepatic function, drug interactions, and the severity of early systemic abnormalities. Severe acidosis, cardiovascular collapse, coagulopathy, progressive organ failure, and major marrow suppression are concerning findings.

Historical dose-response estimates are useful only for broad risk assessment. A patient who has ingested less than 0.8 mg/kg can still become critically ill, while survival above this traditional “lethal” dose is possible with intensive care.

Patients who survive the first several days and demonstrate marrow and cardiovascular recovery often ultimately recover, although prolonged weakness, neuropathy, myopathy, renal dysfunction, or complications of hypoxia and sepsis may persist.

Important Pitfalls

A major pitfall is using the historical gout regimen of repeated hourly colchicine until diarrhea develops. Diarrhea is a sign of toxicity, not a therapeutic endpoint. Current acute-gout treatment is only 1.8 mg total over one hour.

Another important error is believing that only deliberate massive overdoses cause fatal colchicine toxicity. Therapeutic doses can become life-threatening when combined with CYP3A4 or P-gp inhibitors, particularly in renal or hepatic impairment. Clarithromycin is a classic example.

The historical 0.5- and 0.8-mg/kg thresholds should not be interpreted as guarantees of survival or death. Severe poisoning has occurred below these ranges.

An early leukocytosis should not reassure the clinician. Colchicine poisoning can subsequently produce profound leukopenia and pancytopenia several days later.

Improvement in vomiting and diarrhea does not necessarily mean the poisoning is resolving. The patient may be transitioning from gastrointestinal toxicity into the multiorgan-failure phase.

Routine ipecac and gastric lavage are obsolete. Activated charcoal is the more reasonable decontamination strategy after a recent substantial exposure when the airway is safe, with MDAC considered selectively rather than automatically.

Another major pitfall is starting hemodialysis simply to remove colchicine. Dialysis does not meaningfully clear the drug after tissue distribution.

Finally, colchicine-specific Fab fragments are a promising genuine antidotal concept, but they remain experimental and unavailable for routine clinical treatment.

High-Yield Toxicology Pearls

Colchicine poisoning should be remembered as “GI catastrophe first, multiorgan failure second, marrow recovery and alopecia later.” The drug binds tubulin and disrupts microtubules, damaging rapidly dividing tissues as well as myocardium, muscle, and other organs.

Current acute gout therapy is 1.2 mg followed by 0.6 mg one hour later, not repeated hourly dosing until diarrhea. Oral colchicine has a very narrow therapeutic margin, and CYP3A4/P-gp inhibitors—especially clarithromycin and cyclosporine—can cause fatal accumulation even during therapeutic dosing.

Historical dose categories of <0.5 mg/kg, 0.5–0.8 mg/kg, and >0.8 mg/kg are only rough prognostic markers. Severe toxicity can occur below 0.5 mg/kg, and no dose guarantees a particular outcome.

The early phase produces vomiting, abdominal pain, profuse diarrhea, dehydration, and leukocytosis. The dangerous second phase produces cardiovascular collapse, ARDS, hepatic and renal injury, DIC, rhabdomyolysis, neurologic toxicity, and bone-marrow suppression. Neutrophils and platelets may reach their nadir around days 3–7.

Serial CBC and multiorgan laboratory monitoring are therefore essential even after gastrointestinal symptoms improve. Fever during severe neutropenia should be treated as febrile neutropenia/sepsis, and G-CSF may be considered for severe marrow suppression.

There is no commercially available antidote. Colchicine-specific Fab fragments have produced dramatic benefit experimentally and in a rare human case but remain unavailable for routine clinical use.

Activated charcoal should be considered early after a significant ingestion when the airway is safe. Ipecac is obsolete, routine gastric lavage is not recommended, and multiple-dose charcoal remains a specialist-directed option with limited outcome evidence.

Colchicine is not effectively removed by hemodialysis because of extensive tissue distribution. Dialysis should be used for standard renal/metabolic indications rather than as a toxin-removal strategy.

Plant poisoning from Colchicum autumnale and Gloriosa superba can be severe or fatal and should be treated exactly as pharmaceutical colchicine poisoning.

The old Pregnancy Category D classification is obsolete. Therapeutic human pregnancy data do not demonstrate an increased major congenital-malformation or miscarriage risk, and therapeutic colchicine is generally considered compatible with breastfeeding.

The most important clinical warning is:

Severe gastroenteritis after colchicine exposure may be the beginning—not the peak—of the poisoning.