Digoxin toxicity: Difference between revisions

(Major update: DigiFab dosing formulas, empiric vial dosing, bidirectional VT, calcium controversy, hyperkalemia significance, drug interactions, avoid cardioversion, references with PMIDs)
(Remove refs with incorrect PMIDs (verified against PubMed))
 
(2 intermediate revisions by the same user not shown)
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==Background==
==Background==
*Digoxin (digitalis) is a cardiac glycoside used for [[atrial fibrillation]] rate control and [[heart failure]]
*Digoxin (digitalis) is a cardiac glycoside used for [[atrial fibrillation]] rate control and [[heart failure]]
*'''Narrow therapeutic index''' (therapeutic level: '''0.5-2.0 ng/mL''')
*Narrow therapeutic index (therapeutic level: 0.5-2.0 ng/mL)
*Mechanism of action: inhibits Na/K-ATPase → increased intracellular calcium → increased contractility
*Mechanism of action: inhibits Na/K-ATPase → increased intracellular calcium → increased contractility
*Also increases vagal tone (AV nodal blockade)
*Also increases vagal tone (AV nodal blockade)
*Toxicity occurs from:
*Toxicity occurs from:
**'''Acute ingestion''' (intentional overdose, accidental)
**Acute ingestion (intentional overdose, accidental)
**'''Chronic accumulation''' (most common — renal insufficiency, drug interactions, dehydration)
**Chronic accumulation (most common — renal insufficiency, drug interactions, dehydration)
*'''Drug interactions that increase digoxin levels''':
*Drug interactions that increase digoxin levels:
**'''Amiodarone''' (increases level by ~50%), verapamil, diltiazem, quinidine
**Amiodarone (increases level by ~50%), verapamil, diltiazem, quinidine
**Macrolide antibiotics (erythromycin, clarithromycin)
**Macrolide antibiotics (erythromycin, clarithromycin)
**Cyclosporine, itraconazole
**Cyclosporine, itraconazole
*'''Conditions that increase sensitivity to digoxin''':
*Conditions that increase sensitivity to digoxin:
**'''Hypokalemia''' (most important — K and digoxin compete for same binding site)
**Hypokalemia (most important — K and digoxin compete for same binding site)
**Hypomagnesemia, hypercalcemia, hypothyroidism, [[renal failure]]
**Hypomagnesemia, hypercalcemia, hypothyroidism, [[renal failure]]
*Mortality without antidote: up to 20-30% in significant poisoning
*Mortality without antidote: up to 20-30% in significant poisoning
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==Clinical Features==
==Clinical Features==
===GI (Often Earliest)===
===GI (Often Earliest)===
*'''Nausea, vomiting, anorexia''' (most common symptoms)
*Nausea, vomiting, anorexia (most common symptoms)
*Abdominal pain, diarrhea
*Abdominal pain, diarrhea


===Cardiac (Most Dangerous)===
===Cardiac (Most Dangerous)===
*'''Almost ANY dysrhythmia can occur'''
*Almost ANY dysrhythmia can occur
*Classic: '''increased automaticity + decreased conduction'''
*Classic: increased automaticity + decreased conduction
*Most common arrhythmia: '''PVCs'''
*Most common arrhythmia: PVCs
*Highly suggestive rhythms:
*Highly suggestive rhythms:
**'''Bidirectional ventricular tachycardia''' (nearly pathognomonic)
**Bidirectional ventricular tachycardia (nearly pathognomonic)<ref>Smith TW. Digitalis: Mechanisms of action and clinical use. N Engl J Med. 1988;318(6):358-365. PMID 3277052</ref>
**'''Atrial tachycardia with AV block''' (PAT with block)
**Atrial tachycardia with AV block (PAT with block)
**'''Accelerated junctional rhythm'''
**Accelerated junctional rhythm
**'''Regularized atrial fibrillation''' (AF with complete heart block + junctional escape)
**Regularized atrial fibrillation (AF with complete heart block + junctional escape)
*Sinus [[bradycardia]], AV block (1st, 2nd, 3rd degree)
*Sinus [[bradycardia]], AV block (1st, 2nd, 3rd degree)
*'''Ventricular fibrillation''' / '''asystole''' (in severe toxicity)
*Ventricular fibrillation / asystole (in severe toxicity)


===Neurologic===
===Neurologic===
*'''Visual disturbances''': xanthopsia (yellow-green halo vision), blurred vision, photophobia
*Visual disturbances: xanthopsia (yellow-green halo vision), blurred vision, photophobia
*Confusion, delirium, weakness, fatigue
*Confusion, delirium, weakness, fatigue
*Drowsiness
*Drowsiness


===Metabolic===
===Metabolic===
*'''Hyperkalemia''' in acute toxicity (Na/K-ATPase inhibition → K moves extracellularly)
*Hyperkalemia in acute toxicity (Na/K-ATPase inhibition → K moves extracellularly)
**'''K >5.0 in acute digoxin poisoning is a marker of severe toxicity'''
**K >5.0 in acute digoxin poisoning is a marker of severe toxicity
**In chronic toxicity, K is often low (from concurrent diuretic use)
**In chronic toxicity, K is often low (from concurrent diuretic use)


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==Evaluation==
==Evaluation==
*'''ECG''' (look for dysrhythmias, ST changes)
*ECG (look for dysrhythmias, ST changes)
**'''Digitalis effect''' (scooped ST depression, "Salvador Dali mustache") ≠ toxicity
**'''Digitalis effect''' (scooped ST depression, "Salvador Dali mustache") ≠ toxicity
**Digitalis '''toxicity''' = arrhythmias
**Digitalis toxicity = arrhythmias
*'''Digoxin level''':
*Digoxin level:
**Therapeutic: 0.5-2.0 ng/mL
**Therapeutic: 0.5-2.0 ng/mL
**'''Draw level ≥6 hours''' after last dose (allows tissue distribution)
**Draw level ≥6 hours after last dose (allows tissue distribution)
**Level >2.0 suggests toxicity but '''clinical correlation is essential'''
**Level >2.0 suggests toxicity but clinical correlation is essential
**Level may be falsely elevated after Digibind (measures bound + unbound)
**Level may be falsely elevated after Digibind (measures bound + unbound)
*'''BMP''': '''potassium''' (critical — hypokalemia worsens toxicity), creatinine, magnesium, calcium
*BMP: potassium (critical — hypokalemia worsens toxicity), creatinine, magnesium, calcium
*'''Magnesium level''' (hypomagnesemia increases digoxin sensitivity)
*Magnesium level (hypomagnesemia increases digoxin sensitivity)


==Management==
==Management==
===Digoxin-Specific Antibody Fragments (DigiFab/Digibind)===
===Digoxin-Specific Antibody Fragments (DigiFab/Digibind)===
*'''Definitive antidote''' — highly effective
*Definitive antidote — highly effective
*'''Indications for empiric dosing''':
*Indications for empiric dosing:
**'''Life-threatening arrhythmias''' (VT, VF, symptomatic bradycardia, high-grade AV block)
**'''Life-threatening arrhythmias''' (VT, VF, symptomatic bradycardia, high-grade AV block)
**'''Hyperkalemia >5.0 mEq/L''' in acute poisoning
**Hyperkalemia >5.0 mEq/L in acute poisoning
**'''Hemodynamic instability'''
**Hemodynamic instability
**'''Digoxin level >10 ng/mL''' (acute) or >4 ng/mL (chronic) with symptoms
**Digoxin level >10 ng/mL (acute) or >4 ng/mL (chronic) with symptoms
*'''Dosing''':
*Dosing:
**If '''amount ingested known''': # vials = (body load in mg × 0.8) / 0.5
**If amount ingested known: # vials = (body load in mg × 0.8) / 0.5
**If '''level known''': # vials = (level ng/mL × weight kg) / 100
**If level known: # vials = (level ng/mL × weight kg) / 100
**'''Empiric dosing''': '''10-20 vials''' for acute life-threatening toxicity; '''3-6 vials''' for chronic toxicity
**'''Empiric dosing''': '''10-20 vials''' for acute life-threatening toxicity; '''3-6 vials''' for chronic toxicity
**Onset: '''30-60 minutes'''
**Onset: 30-60 minutes
*Each vial binds ~0.5 mg digoxin
*Each vial binds ~0.5 mg digoxin
*Post-Digibind: total digoxin level rises (bound to antibody) but '''free digoxin decreases'''
*Post-Digibind: total digoxin level rises (bound to antibody) but free digoxin decreases


===Supportive Measures===
===Supportive Measures===
*'''Correct hypokalemia''' to >4.0 mEq/L (in chronic toxicity)
*Correct hypokalemia to >4.0 mEq/L (in chronic toxicity)
*'''Correct hypomagnesemia''': magnesium sulfate 2g IV
*Correct hypomagnesemia: magnesium sulfate 2g IV
*'''Calcium''': '''CONTROVERSIAL in digoxin toxicity'''
*Calcium: CONTROVERSIAL in digoxin toxicity
**Traditional teaching: avoid calcium (risk of "stone heart")
**Traditional teaching: avoid calcium (risk of "stone heart")
**Recent evidence suggests risk may be overstated, but '''use with extreme caution'''
**Recent evidence suggests risk may be overstated, but '''use with extreme caution'''
**If hyperkalemic arrest, may give calcium but '''administer Digibind simultaneously'''
**If hyperkalemic arrest, may give calcium but administer Digibind simultaneously
*'''Atropine''' for symptomatic bradycardia: 0.5-1 mg IV (may repeat)
*Atropine for symptomatic bradycardia: 0.5-1 mg IV (may repeat)
*'''Activated charcoal''' if acute ingestion within 1-2 hours and protected airway
*Activated charcoal if acute ingestion within 1-2 hours and protected airway
*'''Avoid electrical cardioversion''' if possible (may precipitate VF in digitalis toxicity)
*Avoid electrical cardioversion if possible (may precipitate VF in digitalis toxicity)
*If cardioversion unavoidable: use '''lowest effective energy'''
*If cardioversion unavoidable: use lowest effective energy


===What to Avoid===
===What to Avoid===
*'''No calcium''' (controversial — may worsen toxicity)
*No calcium (controversial — may worsen toxicity)
*'''No Class IA antiarrhythmics''' (procainamide, quinidine — worsen conduction)
*No Class IA antiarrhythmics (procainamide, quinidine — worsen conduction)
*'''Minimize cardioversion'''
*Minimize cardioversion
*'''No beta-blockers''' (worsen bradycardia/AV block)
*No beta-blockers (worsen bradycardia/AV block)


===Refractory Cases===
===Refractory Cases===
*'''Lidocaine''' (for ventricular arrhythmias not responsive to Digibind)
*Lidocaine (for ventricular arrhythmias not responsive to Digibind)
*'''Phenytoin''' (can improve conduction through AV node; historical use)
*Phenytoin (can improve conduction through AV node; historical use)
*'''Temporary pacing''' for complete heart block refractory to atropine and Digibind
*Temporary pacing for complete heart block refractory to atropine and Digibind
*Consider '''hemodialysis''' — does NOT effectively remove digoxin (highly protein/tissue bound) but may help if Digibind unavailable
*Consider hemodialysis — does NOT effectively remove digoxin (highly protein/tissue bound) but may help if Digibind unavailable


==Disposition==
==Disposition==
*'''Admit all symptomatic patients''' to monitored bed or ICU
*Admit all symptomatic patients to monitored bed or ICU
*'''ICU''' for arrhythmias, hemodynamic instability, or Digibind administration
*ICU for arrhythmias, hemodynamic instability, or Digibind administration
*Continuous telemetry for minimum '''12-24 hours'''
*Continuous telemetry for minimum 12-24 hours
*'''Serial digoxin levels''' are NOT useful post-Digibind (measures total, not free)
*Serial digoxin levels are NOT useful post-Digibind (measures total, not free)
*'''Poison control: 1-800-222-1222'''
*Poison control: 1-800-222-1222


==See Also==
==See Also==

Latest revision as of 10:25, 22 March 2026

Background

  • Digoxin (digitalis) is a cardiac glycoside used for atrial fibrillation rate control and heart failure
  • Narrow therapeutic index (therapeutic level: 0.5-2.0 ng/mL)
  • Mechanism of action: inhibits Na/K-ATPase → increased intracellular calcium → increased contractility
  • Also increases vagal tone (AV nodal blockade)
  • Toxicity occurs from:
    • Acute ingestion (intentional overdose, accidental)
    • Chronic accumulation (most common — renal insufficiency, drug interactions, dehydration)
  • Drug interactions that increase digoxin levels:
    • Amiodarone (increases level by ~50%), verapamil, diltiazem, quinidine
    • Macrolide antibiotics (erythromycin, clarithromycin)
    • Cyclosporine, itraconazole
  • Conditions that increase sensitivity to digoxin:
    • Hypokalemia (most important — K and digoxin compete for same binding site)
    • Hypomagnesemia, hypercalcemia, hypothyroidism, renal failure
  • Mortality without antidote: up to 20-30% in significant poisoning

Clinical Features

GI (Often Earliest)

  • Nausea, vomiting, anorexia (most common symptoms)
  • Abdominal pain, diarrhea

Cardiac (Most Dangerous)

  • Almost ANY dysrhythmia can occur
  • Classic: increased automaticity + decreased conduction
  • Most common arrhythmia: PVCs
  • Highly suggestive rhythms:
    • Bidirectional ventricular tachycardia (nearly pathognomonic)[1]
    • Atrial tachycardia with AV block (PAT with block)
    • Accelerated junctional rhythm
    • Regularized atrial fibrillation (AF with complete heart block + junctional escape)
  • Sinus bradycardia, AV block (1st, 2nd, 3rd degree)
  • Ventricular fibrillation / asystole (in severe toxicity)

Neurologic

  • Visual disturbances: xanthopsia (yellow-green halo vision), blurred vision, photophobia
  • Confusion, delirium, weakness, fatigue
  • Drowsiness

Metabolic

  • Hyperkalemia in acute toxicity (Na/K-ATPase inhibition → K moves extracellularly)
    • K >5.0 in acute digoxin poisoning is a marker of severe toxicity
    • In chronic toxicity, K is often low (from concurrent diuretic use)

Differential Diagnosis

Evaluation

  • ECG (look for dysrhythmias, ST changes)
    • Digitalis effect (scooped ST depression, "Salvador Dali mustache") ≠ toxicity
    • Digitalis toxicity = arrhythmias
  • Digoxin level:
    • Therapeutic: 0.5-2.0 ng/mL
    • Draw level ≥6 hours after last dose (allows tissue distribution)
    • Level >2.0 suggests toxicity but clinical correlation is essential
    • Level may be falsely elevated after Digibind (measures bound + unbound)
  • BMP: potassium (critical — hypokalemia worsens toxicity), creatinine, magnesium, calcium
  • Magnesium level (hypomagnesemia increases digoxin sensitivity)

Management

Digoxin-Specific Antibody Fragments (DigiFab/Digibind)

  • Definitive antidote — highly effective
  • Indications for empiric dosing:
    • Life-threatening arrhythmias (VT, VF, symptomatic bradycardia, high-grade AV block)
    • Hyperkalemia >5.0 mEq/L in acute poisoning
    • Hemodynamic instability
    • Digoxin level >10 ng/mL (acute) or >4 ng/mL (chronic) with symptoms
  • Dosing:
    • If amount ingested known: # vials = (body load in mg × 0.8) / 0.5
    • If level known: # vials = (level ng/mL × weight kg) / 100
    • Empiric dosing: 10-20 vials for acute life-threatening toxicity; 3-6 vials for chronic toxicity
    • Onset: 30-60 minutes
  • Each vial binds ~0.5 mg digoxin
  • Post-Digibind: total digoxin level rises (bound to antibody) but free digoxin decreases

Supportive Measures

  • Correct hypokalemia to >4.0 mEq/L (in chronic toxicity)
  • Correct hypomagnesemia: magnesium sulfate 2g IV
  • Calcium: CONTROVERSIAL in digoxin toxicity
    • Traditional teaching: avoid calcium (risk of "stone heart")
    • Recent evidence suggests risk may be overstated, but use with extreme caution
    • If hyperkalemic arrest, may give calcium but administer Digibind simultaneously
  • Atropine for symptomatic bradycardia: 0.5-1 mg IV (may repeat)
  • Activated charcoal if acute ingestion within 1-2 hours and protected airway
  • Avoid electrical cardioversion if possible (may precipitate VF in digitalis toxicity)
  • If cardioversion unavoidable: use lowest effective energy

What to Avoid

  • No calcium (controversial — may worsen toxicity)
  • No Class IA antiarrhythmics (procainamide, quinidine — worsen conduction)
  • Minimize cardioversion
  • No beta-blockers (worsen bradycardia/AV block)

Refractory Cases

  • Lidocaine (for ventricular arrhythmias not responsive to Digibind)
  • Phenytoin (can improve conduction through AV node; historical use)
  • Temporary pacing for complete heart block refractory to atropine and Digibind
  • Consider hemodialysis — does NOT effectively remove digoxin (highly protein/tissue bound) but may help if Digibind unavailable

Disposition

  • Admit all symptomatic patients to monitored bed or ICU
  • ICU for arrhythmias, hemodynamic instability, or Digibind administration
  • Continuous telemetry for minimum 12-24 hours
  • Serial digoxin levels are NOT useful post-Digibind (measures total, not free)
  • Poison control: 1-800-222-1222

See Also

References

  • Hauptman PJ, Kelly RA. Digitalis. Circulation. 1999;99(9):1265-1270. PMID 10069797
  • Hack JB, Lewin NA. Cardioactive steroids. In: Goldfrank's Toxicologic Emergencies. 10th ed. McGraw-Hill. 2015.
  • Chan BS, Buckley NA. Digoxin-specific antibody fragments in the treatment of digoxin toxicity. Clin Toxicol. 2014;52(8):824-836. PMID 25089630
  • Levine M, et al. The effects of intravenous calcium in patients with digoxin toxicity. J Emerg Med. 2011;40(1):41-46. PMID 18814997
  1. ↑ Smith TW. Digitalis: Mechanisms of action and clinical use. N Engl J Med. 1988;318(6):358-365. PMID 3277052
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