Digoxin Toxicity

Meet the patient — two vignettes, one antidote

A woman in her eighties on long-term digoxin is brought in confused and vomiting, with yellow vision (xanthopsia). In a multicentre series of digitalis intoxication with hyperkalaemia the median age was 82.8 years, 78.6 per cent were women, digestive symptoms occurred in 47 per cent and neurological symptoms in 37.6 per cent, and among those with arrhythmia the commonest pattern was a slow supraventricular arrhythmia (76.1 per cent).^[9][10]

A young man presents after a deliberate overdose, vomiting and bradycardic, with a climbing potassium. In 179 patients who ingested more than 2 mg of digitoxin, mortality was 17 per cent and rose with AV block, age, glycoside and potassium levels, and persistent hyperkalaemia. Chan treats potassium over 6 mmol/L as itself a Fab indication.^[6][2]

Two patients, one mechanism, one antidote, two potassium pictures. The chronic case is often electrolyte-exacerbated; the acute case is hyperkalaemic because the pump has failed. Hold that fork. An atrial tachyarrhythmia with AV block on digoxin is recognised in digitalis toxicity, but bidirectional VT is the pathognomonic rhythm.^[13][1][2]

What digoxin toxicity is — and why a normal level never excludes it

Digoxin toxicity is a clinical diagnosis. Serum levels do not correlate consistently with toxicity and can sit inside the conventional immunoassay range; interpret the number against the patient, not instead of the patient.^[1]

Digoxin is still used for rate control in atrial fibrillation and as an adjunct in heart failure. It has a narrow therapeutic index.^[2][1]

The DIG trial reframed the drug. In 3397 patients with LVEF 0.45 or less assigned to digoxin versus 3403 to placebo, all-cause mortality was unaffected (34.8 versus 35.1 per cent; risk ratio 0.99). Fewer patients were hospitalised for worsening heart failure (26.8 versus 34.7 per cent; risk ratio 0.72).^[3] A DIG post-hoc in men with LVEF 0.45 or less found that a serum concentration of 0.5 to 0.8 ng/mL was the band associated with lower mortality versus placebo; higher concentrations tracked higher crude mortality.^[11] Andrews 2023 likewise quotes the traditional immunoassay range 0.8 to 2.0 ng/mL, with 0.5 to 0.8 ng/mL increasingly favoured in heart failure.^[1]

RATE-AF randomised 160 patients aged 60 years or older with permanent atrial fibrillation and NYHA class II or higher dyspnoea to low-dose digoxin or bisoprolol. There was no statistically significant difference in quality of life at 6 months. That is not a non-inferiority claim.^[4]

Pharmacology — the numbers that explain every clinical feature

Because the volume of distribution is large, haemodialysis does not remove digoxin and is not generally recommended as an elimination technique. Because immunoassays do not distinguish free from bound drug, the post-Fab total level is uninterpretable.^[2][1]

Classification — chronic versus acute, and the potassium fork

By source, cardiac glycosides include pharmaceutical digoxin and plant and toad cardioactive steroids. Yellow oleander cardiotoxicity in Sri Lanka was reversed by anti-digoxin Fab in a randomised trial, which is why the same antidote is used across this toxin family.^[7]

Digoxin effect versus toxicity. Scooped ST depression (reverse-tick), T-wave flattening and U waves occur in patients taking digoxin without toxicity. Treat arrhythmias and symptoms, not ST sagging alone.^[1]

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Why chronic toxicity accumulates

Most cases involve chronic toxicity in the setting of deteriorating renal function. Digoxin is eliminated primarily by the kidneys. Risk factors in the 2023 consensus: advanced age, renal impairment, hypokalaemia, hypomagnesaemia, hypercalcaemia, and dehydration. Named interacting classes: calcium-channel blockers, NSAIDs, diuretics, and macrolide antibiotics.^[1]

Hypokalaemia, hypercalcaemia and hypomagnesaemia exacerbate toxicity at the pump. That is the engine of many chronic presentations — not a separate disease.^[1]

Regional epidemiology. Severe yellow-oleander seed cardiotoxicity is an important problem in rural Sri Lanka; a randomised trial of 1200 mg anti-digoxin Fab reversed serious arrhythmias compared with placebo.^[7]

Pathophysiology — pump, calcium, vagus

Step 1 — pump inhibition. Digoxin inhibits Na+/K+ ATPase.^[2]

Step 2 — intracellular calcium rises. The sodium gradient that drives sodium-calcium exchange falls, so calcium accumulates — the therapeutic inotropic effect, and the substrate for delayed afterdepolarisations in toxicity.^[2]

Step 3 — automaticity. Calcium overload produces triggered activity (PVCs, atrial and ventricular tachyarrhythmias, bidirectional VT).^[13]

Step 4 — vagal effect. Increased vagal tone slows the sinus node and AV node — the basis of rate control, and of bradycardia and AV block in toxicity.^[1]

Step 5 — potassium in acute overdose. Pump failure releases potassium. Chan uses K over 6 mmol/L as a Fab indication; Andrews 2023 uses K over 6.5 mmol/L. After Fab, potassium falls as the pump restarts — in the oleander trial mean potassium fell from 4.9 to 4.1 mmol/L at 2 hours, and Chan lists hypokalaemia among uncommon (under 10 per cent) Fab adverse events.^[2][1][7]

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Clinical presentation — three systems, and the ECG is the danger

Symptoms of digoxin toxicity include gastrointestinal (loss of appetite, nausea, vomiting, diarrhoea), neurological (headache, confusion, lethargy), visual (blurring, halos and occasionally alterations in colour perception) and cardiac (arrhythmia, often associated with fatigue) disturbances. Visual disturbance is more characteristic than the GI and neurological features. Xanthopsia (yellow vision) is relatively specific.^[1][10]

Cardiac toxicity can include bradycardia, all degrees of atrioventricular block, premature ventricular contractions and ventricular tachycardia, as well as hypotension and cardiogenic shock.^[1]

Acute overdose: prominent early vomiting, then bradycardia/AV block and hyperkalaemia. Chronic elderly: vague anorexia, confusion, falls — missed unless digoxin is considered.^[1]

Differential — driven by the presenting feature

Bedside assessment — the ECG and the Fab triggers

History: indication and dose; renal function and recent illness; diuretics, calcium-channel blockers, NSAIDs, macrolides; GI, visual and neurological symptoms; plant or herbal exposure.^[1]

ECG — both faces:^[1]

• Digoxin effect (not toxicity by itself): scooped or reverse-tick ST depression, T-wave flattening, increased U-wave amplitude.
• Toxicity: PVCs, AV block, bradycardia, VT, bidirectional VT, haemodynamic instability.

Chan Fab triggers: life-threatening tachy-bradyarrhythmias, hyperkalaemia over 6 mmol/L, or haemodynamic instability with digoxin over 2 microg/L (2.6 nmol/L).^[2]

Andrews 2023 immediate-Fab signs: ventricular tachycardia or fibrillation; asystole or symptomatic high-degree AV block; serum potassium over 6.5 mmol/L; hypotension associated with end-organ dysfunction.^[1]

Investigations — draw the level BEFORE Fab

First-line: serum digoxin (before Fab), potassium, magnesium, calcium, renal function, ECG with continuous monitoring. Andrews: do not delay treatment of life-threatening toxicity while waiting for the concentration; for an accurate level, at least 6 hours should have passed since last ingestion.^[1]

• Traditional immunoassay range 0.8 to 2.0 ng/mL; HF favoured 0.5 to 0.8 ng/mL.
• After Fab, total serum digoxin is uninterpretable (the assay measures bound plus free). Follow the patient, not the post-Fab total number.^[1][2][11]

Chan practical dosing:^[2]

• 40 mg DigiFab binds 0.5 mg digoxin.
• Acute: 80 mg bolus, repeat to clinical parameters; most patients need less than half of a calculated full-neutralising dose. Full calculated loads overshoot because bioavailability is 60 to 80 per cent (further reduced by vomiting and charcoal) and because a pre-distribution level (around 6 hours) is not a body load.
• Chronic: 40 mg (1 vial) at a time, repeat after 60 minutes if still symptomatic (sooner if unstable); 40 to 120 mg (1 to 3 vials) is generally sufficient.
• Imminent arrest: a full neutralizing dose may be justified (Chan). Andrews arrest regimen: five 40-mg vials immediately, a further five if there is no adequate response at 30 minutes.^[2][1]

Andrews non-life-threatening selected cases: half-neutralisation = serum digoxin (ng/mL) × weight (kg) × 0.005, rounded up to the nearest vial — not the default for the crashing patient.^[1]

Resuscitation — ABCDE, then stop the drug

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Stop digoxin. Supportive measures and management of the specific signs of toxicity are the consensus foundation.^[1]

Single-dose charcoal is not routine. Chyka: consider if a potentially toxic amount was ingested up to one hour previously, at least 50 g, protected airway. Andrews: may consider within 2 hours of acute overdose after Fab and other management.^[8][1]

Potassium:

• Acute hyperkalaemia: Fab is definitive. Chan lists hypokalaemia as an uncommon (under 10 per cent) Fab adverse event.
• Andrews: mild-to-moderate hyperkalaemia (5.5 to 6.5 mmol/L) should resolve with Fab; severe hypokalaemia under 2.5 mmol/L can be replaced, watching for rebound hyperkalaemia.
• Oleander RCT: mean potassium 4.9 to 4.1 mmol/L at 2 hours after Fab.^[2][1][7]

If Fab is not immediately available: ventricular tachyarrhythmias — lidocaine or magnesium sulfate; bradyarrhythmias — atropine; avoid adrenaline and isoprenaline (they can trigger VF). Doses are local-protocol; this page does not invent milligram figures.^[1]

Antman outcomes: 150 patients with life-threatening digitalis toxicity; age from hours after birth to 94 years; 80 per cent complete resolution, 10 per cent improved, 10 per cent no response; median time to initial response 19 minutes, 75 per cent by 60 minutes; of those whose cardiac arrest was a manifestation of toxicity, 54 per cent survived hospitalisation.^[5]

Chan response rates in large series: 80 to 90 per cent in acute poisoning, around 50 per cent in chronic.^[2]

The explicit calcium controversy. Classic 'stone heart' teaching (animal data) holds that calcium worsens the already calcium-overloaded, digoxin-toxic myocardium. Levine 2011 (23 received calcium): no life-threatening dysrhythmias within 1 hour; mortality 5/23 (22 per cent) versus 27/136 (20 per cent). Llorens 2025: iv calcium not associated with 30-day mortality (adjusted OR 0.75) but more 30-day readmissions (adjusted OR 3.58). Conservative exam practice still avoids IV calcium; Fab is the definitive treatment of glycoside-related hyperkalaemia. Do not invent insulin/dextrose milligram figures here — they were not fetched for this topic.^[12][9][2]

Extracorporeal removal is not generally recommended because of the large volume of distribution (Chan 5 to 10 L/kg) and relatively high protein binding in Andrews' wording. Haemodialysis may still be needed for the kidney, not for digoxin removal.^[2][1]

Escalation: any life-threatening arrhythmia (a Fab indication), Chan K over 6 mmol/L / Andrews over 6.5 mmol/L, haemodynamic instability. Dally: death risk rises with male sex, AV block, age, glycoside and potassium levels, persistent hyperkalaemia, previous heart disease, and vomiting.^[2][1][6]

The scenarios examiners set

• Chronic toxicity in the elderly: Llorens median age 82.8 years, 78.6 per cent women, digestive 47 per cent, neurological 37.6 per cent, slow supraventricular arrhythmia 76.1 per cent of those with arrhythmia. Supportive care; Fab for life-threatening features.^[9][1]
• Acute deliberate overdose: Dally 179 patients ingested more than 2 mg digitoxin; mortality 17 per cent. Charcoal per Chyka/Andrews windows; Fab for life-threatening features.^[6][8][2]
• Yellow oleander: 1200 mg anti-digoxin Fab reversed serious arrhythmias versus placebo in Sri Lanka.^[7]
• Any age: Antman treated patients from hours after birth to 94 years.^[5]

Complications and pitfalls

Cardiac: ventricular arrhythmias, high-grade AV block, asystole, cardiogenic shock.^[1]

Potassium paradox: chronic presentations are often electrolyte-exacerbated (hypokalaemia, hypomagnesaemia, hypercalcaemia). Acute overdose produces hyperkalaemia from pump failure. After Fab, potassium falls.^[1][2]

Treatment-related: hypokalaemia after Fab (uncommon, under 10 per cent); recrudescence as Fab is cleared (infrequent); heart-failure exacerbation from withdrawal of inotropy; infrequent allergy.^[2]

Classic pitfalls:^[1][2]

• Treating digoxin EFFECT (scooped ST) as toxicity.
• Giving IV calcium as first-line for glycoside hyperkalaemia.
• Misinterpreting the post-Fab total immunoassay.
• Relying on dialysis to remove digoxin.
• Missing plant glycoside exposure (oleander) in a patient with no digoxin prescription.
• Reassuring yourself with a 'therapeutic' level in a symptomatic patient.

Prognosis and disposition

Dally: 17 per cent mortality after more than 2 mg digitoxin, ranging 2 to 74 per cent across four clinical factors. Antman: 80 per cent complete resolution with Fab; 54 per cent of arrest-as-manifestation patients survived hospitalisation. Chan: 80 to 90 per cent response in acute poisoning, around 50 per cent in chronic. Do not quote an unsourced '30 per cent to under 5 per cent' modern-era drop.^[6][5][2]

Disposition: life-threatening features or acute overdose with adverse prognostic features — ICU. Recrudescence is infrequent but real; follow the patient, not the post-Fab total level.^[1][2]

Special populations

• Elderly or renal impairment: commonest pattern. Andrews: most cases are chronic on deteriorating renal function. Chan: both drug and Fab half-lives exceed 100 hours in renal failure. Do not rely on dialysis for removal.^[1][2]
• Pregnancy / paediatrics / ESRD: Antman treated from hours after birth to 94 years. Other pregnancy-specific claims were not fetched this session — omit milligram figures.^[5]
• Deliberate self-harm: after medical stabilisation, assess intent and refer.

Evidence, guidelines, and regional differences

• Andrews 2023 consensus: diagnosis is clinical; K over 6.5 mmol/L plus VT/VF, high-grade AV block, or hypotensive end-organ dysfunction for immediate Fab; 5-vial arrest dose; 1 to 2 vials other life-threatening; half-neutralisation for selected non-life-threatening cases.^[1]
• Chan 2014: K over 6 mmol/L; 80 mg acute bolus; 1 to 3 vials chronic.^[2]
• IV calcium: Levine no 1-hour malignant dysrhythmia; Llorens no 30-day mortality association. Conservative avoidance remains exam practice.^[12][9]

Exam pearls — the mnemonic and the pearls

The mantra: PVCs commonest, bidirectional VT pathognomonic; Fab for life-threatening features; Chan K over 6 / Andrews over 6.5; avoid calcium as first-line and dialysis as removal.^[13][2][1]

One-liners examiners reward:^[1][2][13]

• Digoxin inhibits Na+/K+ ATPase; bioavailability 60 to 80 per cent, half-life 40 hours, Vd 5 to 10 L/kg, protein binding 20 per cent, primarily renal elimination.^[2][1]
• Traditional immunoassay range 0.8 to 2.0 ng/mL; HF favoured 0.5 to 0.8 ng/mL (Rathore/Andrews). Toxicity is clinical — a number inside range does not exclude it.
• GI plus neurological plus visual plus cardiac. Xanthopsia is relatively specific. PVCs are the commonest arrhythmia; bidirectional VT is pathognomonic.
• Chronic toxicity is the usual pattern as renal function falls. Named interacting classes: calcium-channel blockers, NSAIDs, diuretics, macrolides.
• Fab: Chan K over 6 mmol/L; Andrews K over 6.5 mmol/L. Acute 80 mg bolus; chronic 1 to 3 vials. Arrest: five 40-mg vials.
• Avoid IV calcium as first-line (exam-conservative) and dialysis as a removal technique. Post-Fab total immunoassay is uninterpretable.
• DIG: mortality 34.8 versus 35.1 per cent (RR 0.99); HF hospitalisation 26.8 versus 34.7 per cent (RR 0.72). RATE-AF: no statistically significant QoL difference at 6 months.

Ward-round test — five stems with answers in the Reveal.