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Key Features

Essentials of Diagnosis

  • Intoxication may result from

    • Acute single exposure

    • Chronic accumulation from accidental overmedication, especially in patients with kidney disease taking digoxin

  • Hyperkalemia common after acute overdose

  • Many different arrhythmias can occur

General Considerations

  • Cardiac glycosides paralyze the Na+-K+-ATPase pump and have potent vagotonic effects

  • Intracellular effects

    • Enhancement of calcium-dependent contractility

    • Shortening of the action potential duration

  • Older age and chronic kidney disease are associated with greater risk of digoxin toxicity

  • Bufotenin, a cardiotoxic steroid found in certain toad secretions and used as an herbal medicine and a purported aphrodisiac, has pharmacologic properties similar to cardiac glycosides

Clinical Findings

Symptoms and Signs

Acute overdose

  • Nausea and vomiting

  • Bradycardia

  • Atrioventricular (AV) block

  • Hyperkalemia

Chronic overingestion

  • Hypokalemia and hypomagnesia are more likely owing to concurrent diuretic treatment

  • Ventricular arrhythmias; for example

    • Ectopy

    • Bidirectional ventricular tachycardia

    • Ventricular fibrillation

Diagnosis

Laboratory Tests

  • Serum digoxin level (Note: Levels drawn within 6 h of ingestion may be falsely elevated before complete tissue distribution)

  • Serum potassium (frequent measures useful because they correlate with tissue effects)

Diagnostic Procedures

  • Continuous ECG monitoring

  • Pacemaker may be needed

Treatment

  • After acute ingestion

    • Administer activated charcoal

      • Dose: 60–100 g orally or via gastric tube, mixed in aqueous slurry; repeated doses may be given

      • Do not use for comatose or convulsing patients unless it can be given by gastric tube and the airway is protected by cuffed endotracheal tube

    • Monitor potassium levels and cardiac rhythm closely

    • Treat bradycardia initially with atropine (0.5–2 mg intravenously) or a transcutaneous external cardiac pacemaker

  • Severe intoxication: administer digoxin-specific antibodies [digoxin immune Fab (ovine) DigiFab]

  • Dose is estimated based on body burden of digoxin calculated from ingested dose or steady-state serum digoxin concentration

    • Ingested dose

      • Number of vials = ~1.5–2 × ingested dose (mg)

    • Serum concentration

      • Number of vials = serum digoxin (ng/mL) × body weight (kg) × 10–2

      • Note: This is based on equilibrium digoxin level; after acute overdose, serum levels are falsely high for several hours before tissue distribution is complete, and overestimation of DigiFab dose is likely

    • More effective binding of digoxin may be achieved if the dose is given partly as a bolus and the remainder as an infusion over a few hours

  • Empiric titration of DigiFab

    • May be used if patient's condition is relatively stable and an underlying condition (eg, atrial fibrillation) favors retaining a residual level of digitalis activity

    • Start with one or two vials and reassess clinical condition after 20–30 ...

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