Why this poison is interesting

Quinine is the overdose that threatens two organs the patient most wants to keep: the retina, where visual loss can be irreversible, and the heart, where sodium-channel blockade produces a cardiotoxicity that behaves like the tricyclics'. It announces itself with cinchonism — tinnitus, deafness, headache and disturbed vision — and in serious overdose adds convulsions, coma, arrhythmia and cardiogenic shock, with hypoglycaemia and hypokalaemia underneath.²

It blocks cardiac sodium channels. Quinine is a sodium-channel blocker in the same membrane-stabilising family as the tricyclics, so it widens the QRS and prolongs the QT, predisposing to ventricular arrhythmia — which is why it belongs with the library's sodium-channel blockade group and why bicarbonate has a role.² Established
It is directly retinotoxic. Serious overdose can cause visual loss that may be irreversible — an organ-specific toxicity that makes quinine poisoning uniquely feared among the antimalarials.² Established
It is the poison made worse by the wrong removal. Dialysis does not help and EXTRIP recommends against it,¹ but multiple-dose activated charcoal does enhance elimination² — a rare instance where the gut, not the dialyser, is the removal route that works.

Quinine attacks the two organs a patient can least spare — and the instinct to dialyse is exactly the instinct to resist.

The toxic principle

Quinine has three toxic actions running at once: sodium-channel blockade in the heart, direct retinal toxicity, and stimulation of insulin release. The first two define the danger; the third is the metabolic complication that can catch the unwary.

Sodium-channel blockade slows cardiac conduction. Quinine is a membrane-stabilising, quinidine-like agent; blocking the fast sodium channel widens the QRS, and its effect on repolarisation prolongs the QT, so both conduction delay and a torsades risk are present.² Established
Direct retinal toxicity threatens vision. Serious overdose can cause disturbed vision progressing to visual loss that may be irreversible — a toxicity specific to the eye and one of the defining hazards of quinine poisoning.² Established
Insulin release causes hypoglycaemia. Quinine stimulates pancreatic insulin secretion, so hypoglycaemia is a recognised feature of serious overdose (and of quinine use in malaria), alongside hypokalaemia.² Established

Toxicokinetics

Quinine — rapidly absorbed, highly bound, and not a dialysis target
Parameter	Therapeutic	In overdose	Why it changes
Absorption	Rapidly and almost completely absorbed; peak plasma concentration about 1–3 hours after oral sulfate²	Rapid, so cinchonism and early features appear within hours	Fast absorption means the cardiotoxic and cinchonism features declare themselves early; the label advises observation for at least 12 hours, reflecting how quickly and for how long the danger runs.
Protein binding	About 70% in healthy subjects, rising to 90% or more in malaria²	High, and higher still in malaria — little free drug for a dialyser	The substantial protein binding is one reason extracorporeal removal is unrewarding, and it rises further in the malaria-infected patient, the very population quinine is used to treat.
Distribution	Widely distributed; CSF concentrations in cerebral malaria about 2–7% of plasma; volume of distribution reduced by malaria infection²	Widely distributed into tissues, limiting the blood-borne fraction available for removal	Wide tissue distribution, like the high binding, keeps the drug out of the blood compartment a dialyser can clean — the same reasoning that defeats removal for many lipophilic, bound poisons.
Metabolism	Extensively metabolised in the liver²	Hepatic clearance dominates; malaria reduces clearance	Because elimination is mainly hepatic metabolism rather than renal excretion of unchanged drug, there is little to gain from forcing a renal or dialytic route — the body clears quinine by metabolism, which removal cannot accelerate.
Elimination	Mainly urinary after metabolism; less than 5% to about 20% excreted unchanged; elimination half-life about 11 hours, prolonged in malaria; excretion increased in acid urine²	Half-life long enough to require prolonged monitoring; multiple-dose activated charcoal enhances elimination²	The ~11 h half-life underlies the observation period, and multiple-dose activated charcoal is the removal method that works — interrupting enterohepatic and enteroenteric recirculation from the gut, where a dialyser cannot reach.
Dialysability	—	Not a useful target — EXTRIP recommends against extracorporeal treatment (1D); MDAC is the effective removal route¹²	High protein binding and wide tissue distribution make dialysis ineffective, and EXTRIP recommends against it;¹ the label's endorsement of multiple-dose activated charcoal points to the gut, not the blood, as the route by which quinine can actually be removed.

Metabolism and the metabolites

Quinine is extensively metabolised by the liver and excreted mainly in the urine, with only a small fraction unchanged.² There is no toxic metabolite driving the overdose picture; the parent alkaloid is the poison, and the clinically useful point about its handling is that its elimination can be hastened from the gut with multiple-dose activated charcoal but not from the blood with a dialyser.

Quinine — a parent-drug poison cleared by the liver, removable only from the gut

Quinine (ingested)Toxic as the parent alkaloid — sodium-channel blockade, retinotoxicity, insulin release²
Hepatic metabolismInactive metabolites (urinary)The major exit; <5–20% excreted unchanged; half-life ~11 h, longer in malaria²
Gut (enterohepatic/enteroenteric recirculation)Re-presented to the gut lumenWhere multiple-dose activated charcoal acts to enhance elimination²

What changes the answer

Malaria itself — raises protein binding and reduces the volume of distribution and clearance, altering quinine handling in the infected patient.² Established
Urinary pH — excretion of unchanged quinine increases in acid urine,² a minor pharmacological point rather than a therapeutic lever.
Co-ingested QT-prolonging or sodium-channel-blocking drugs compound the cardiotoxicity. Inferred
Time to decontamination — because visual loss may be irreversible and is absorption-dependent, the window for limiting uptake matters more than usual.²

Elimination and accumulation

Quinine is cleared by hepatic metabolism with a half-life around 11 hours, longer in malaria.² It does not accumulate like a renally-dependent poison, but it persists long enough to require prolonged cardiac and visual monitoring, and its removal — where removal helps at all — is achieved from the gut, not the blood.

The EXTRIP position

EXTRIP recommends against extracorporeal treatment in severe quinine poisoning (strong recommendation, very low quality evidence, 1D).¹ The recommendation reflects the drug's high protein binding and wide distribution — there is little in the blood to remove — and stands in deliberate contrast to the one removal route that does work, the gut.

Against dialysis (1D) — quinine is too protein-bound and too widely distributed for extracorporeal removal to be worthwhile.¹
For multiple-dose activated charcoal — the label states it enhances quinine elimination,² making the gut the effective removal route.
Supportive and sodium-channel-directed care otherwise — sodium bicarbonate for the wide-QRS cardiotoxicity, management of arrhythmia, glucose for hypoglycaemia, and monitoring of cardiac conduction, electrolytes, glucose and visual acuity.²

Target organs — and why those

Retina / eye

TargetRetinal neurons (direct retinotoxicity)

Why hereQuinine is directly toxic to the retina, and serious overdose can cause visual loss that may be irreversible.² Established

At the bedsideBlurred vision and disturbed colour vision early, progressing in serious cases to constricted fields and visual loss that may not recover.² Visual acuity is monitored, and the irreversibility is what makes limiting absorption important.

Heart

TargetCardiac fast sodium channel and repolarisation

Why hereQuinine blocks the fast sodium channel (a quinidine-like, membrane-stabilising effect) and prolongs repolarisation, widening the QRS and the QT.² Established

At the bedsideQT prolongation, ventricular arrhythmia (including torsades, typically later), cardiogenic shock and, in severe poisoning, cardiac arrest.²³ A wide QRS triggers sodium bicarbonate, as elsewhere in the sodium-channel blockade family.

Pancreas / glucose homeostasis

TargetPancreatic beta-cell insulin release

Why hereQuinine stimulates insulin secretion, lowering blood glucose.² Established

At the bedsideHypoglycaemia in serious overdose (and during quinine treatment of malaria), which must be sought and corrected; glucose is monitored alongside the ECG.²

Auditory system

TargetCochlear function (cinchonism)

Why hereQuinine affects the cochlea, producing the tinnitus and reversible hearing loss that are part of cinchonism.² Established

At the bedsideTinnitus and deafness, usually reversible, as part of the early cinchonism syndrome with headache, nausea and disturbed vision — a marker of significant exposure.²

Timeline of effects

Quinine declares itself within hours as cinchonism, and in serious overdose the cardiotoxicity and visual loss follow, with hypoglycaemia and hypokalaemia underneath. The course runs over the drug's half-life, which is why monitoring is prolonged and why torsades in particular can appear later than the first arrhythmias.

Quinine — cinchonism first, then the heart and the eyes

Time

What you seeWhat is happening

0–4 hCinchonism
What you seeNausea and vomiting, tinnitus, deafness, headache, flushing and disturbed vision — the cinchonism syndrome, appearing as the drug is absorbed.
What is happeningRapid, near-complete absorption (peak 1–3 h) delivers the alkaloid; cochlear and early visual effects and gastrointestinal upset mark significant exposure.²
4–24 hCardiotoxicity and visual loss
What you seeIn serious overdose: QT prolongation and ventricular arrhythmia, cardiogenic shock, convulsions, impaired consciousness and coma; progressive visual loss that may be irreversible; hypoglycaemia and hypokalaemia.
What is happeningSodium-channel blockade widens the QRS and, with prolonged repolarisation, sets up arrhythmia; direct retinotoxicity threatens sight; insulin release lowers glucose.²³ Ventricular tachycardia and fibrillation tend to occur early in this family, with torsades developing later.³
Over the half-lifeMonitoring and resolution
What you seeWith supportive and sodium-channel-directed care the cardiotoxicity is managed across the drug's ~11 h half-life; hearing and some visual disturbance may recover, but established visual loss may not. Observation for at least 12 hours is advised.²
What is happeningAs the liver metabolises the alkaloid and multiple-dose activated charcoal hastens its removal from the gut, the sodium-channel and pancreatic effects recede; the retinal injury, being direct neuronal toxicity, may be permanent.² Established

What the mechanism predicts at the bedside

Why a wide QRS means bicarbonate

Quinine is a sodium-channel blocker, so a widening QRS is the signature of significant cardiotoxicity and the conventional trigger for sodium bicarbonate, exactly as in the tricyclic antidepressant and broader sodium-channel blockade group.² Reading quinine as a member of that family tells you what to watch on the ECG and what to reach for. Established

Why dialysis is the wrong removal and charcoal the right one

Quinine is highly protein-bound and widely distributed, so there is little free drug in the blood for a dialyser to take, and EXTRIP recommends against extracorporeal treatment.¹ Multiple-dose activated charcoal, by contrast, enhances elimination by trapping the drug as it recirculates through the gut.² The mechanism says the removal route is enteral, not extracorporeal.

Why the eyes and the glucose must be checked, not just the heart

The same alkaloid that blocks the sodium channel is directly retinotoxic and stimulates insulin release,² so quinine poisoning is a three-organ problem. A management focused only on the arrhythmia misses the irreversible visual loss and the hypoglycaemia — which is why visual acuity and blood glucose are monitored alongside the ECG. Established

Why limiting absorption matters more than usual

Because the retinal injury may be permanent and is related to the dose absorbed,² reducing further absorption — the rationale for activated charcoal — carries a weight it does not have for poisons whose damage is fully reversible. There is no antidote to undo established visual loss, so prevention is the only protection the eye has.

The antidote, from the poison's side

Quinine has no specific antidote; its three toxic actions are direct effects of the intact alkaloid with no reversible target. What stands in an antidote's place is a combination borrowed from elsewhere in the library — sodium bicarbonate for the sodium-channel cardiotoxicity — plus glucose for the hypoglycaemia and multiple-dose activated charcoal for removal.

Sodium bicarbonate for the wide-QRS cardiotoxicity, as for the other sodium-channel blockade agents — the nearest thing to a mechanism-directed cardiac treatment.² Established
Multiple-dose activated charcoal to enhance elimination, the removal route that works where dialysis does not.²
Glucose for the hypoglycaemia, which is driven by quinine's stimulation of insulin release and must be actively sought.²
No reversal for established visual loss — the retinal toxicity cannot be undone, which is why limiting absorption and supporting the patient through the cardiotoxicity are the whole of the definitive care.²

Critical appraisal

The sodium-channel-blockade account of the cardiotoxicity is well established and clinically load-bearing.² It places quinine firmly with the tricyclics and the rest of the sodium-channel blockade family, explains the wide QRS and the QT, and justifies sodium bicarbonate — the page's main cardiac recommendation.
The irreversible visual loss is stated by the label and is the page's distinguishing claim.² Established That it may be permanent is what separates quinine from the other sodium-channel blockers and what makes limiting absorption matter; the page is careful to say 'may be irreversible' rather than asserting invariable permanence.
The hypoglycaemia mechanism is well supported. Established Quinine-stimulated insulin release is recognised both in overdose and in malaria treatment,² and the page flags it as a third organ system precisely because a cardiac-focused management tends to miss it.
The EXTRIP 'against' recommendation is strong (1D) and coherent with the chemistry.¹ High protein binding and wide distribution make removal unrewarding; the page contrasts this deliberately with the label's support for multiple-dose activated charcoal,² and an auditor should check that the two are not conflated — they are different routes with opposite verdicts.
The torsades-timing note is borrowed from the sister antimalarial label and should be read as family behaviour. Inferred The statement that ventricular tachycardia and fibrillation occur early while torsades develops later comes from the chloroquine label's overdose section;³ it is applied to quinine as shared sodium-channel-blocker behaviour, and the page attributes it rather than claiming it as quinine-specific data.
Fatal-dose figures were deliberately withheld. The label prints them, including for children; the page does not, routing the quantities to TOXBASE and NPIS in keeping with the library's editorial boundary.

References

1
EXTRIP Workgroup. Berling I, King JD, Shepherd G, et al. Extracorporeal Treatment for Chloroquine, Hydroxychloroquine, and Quinine Poisoning: Systematic Review and Recommendations from the EXTRIP Workgroup. J Am Soc Nephrol 2020;31(10):2475–89. PubMed 32963091 · recommendation set at extrip-workgroup.org/quinine-chloroquine. Source of the strong recommendation, on very low quality evidence (1D), against extracorporeal treatment in severe quinine poisoning. Read from the workgroup's published recommendation page; verified 13 Sep 2026.
2
Quinine Sulfate Tablets BP 300 mg — Summary of Product Characteristics. emc product 14316. §4.9 and §5.2 fetched and read in full. Source of the cinchonism features (tinnitus, deafness, headache, vasodilation, disturbed vision), the statement that overdose may cause irreversible visual loss and can be fatal, the features of significant overdose (convulsions, impaired consciousness, coma, respiratory depression, QT prolongation, ventricular arrhythmia, cardiogenic shock, renal failure, hypokalaemia, hypoglycaemia), the advice to monitor cardiac conduction and rhythm, electrolytes, glucose and visual acuity and to observe for at least 12 hours, the statement that multiple-dose activated charcoal enhances quinine elimination, the rapid near-complete absorption with a 1–3 h peak, the ~70% protein binding rising to ≥90% in malaria, the wide distribution with CSF 2–7% of plasma, the extensive hepatic metabolism with <5–20% excreted unchanged, the ~11 h half-life prolonged in malaria, and the increased excretion in acid urine. Fatal-dose figures in the label were deliberately not reproduced. Verified 13 Sep 2026.
3
Avloclor Tablets (chloroquine phosphate) — Summary of Product Characteristics, Alliance. emc product 5490. §4.9 consulted for the statement, applied here as shared sodium-channel-blocker behaviour in the cinchona/4-aminoquinoline family, that ventricular tachycardia and fibrillation tend to occur early while torsades de pointes develops later. Verified 13 Sep 2026.
4
TOXBASE — quinine. National Poisons Information Service. toxbase.org (NHS login required. NPIS: 0344 892 0111. The authoritative UK source for referral and observation thresholds, decontamination, indications for sodium bicarbonate, and management of arrhythmia, hypoglycaemia and electrolyte disturbance. Login-gated, so not quoted here.)

Quinine

At a glance