Digoxin Toxicity 

 

 

Background 

 

  • Digoxin works by ultimately ↑ cardiac myocyte Ca+

  • Excessive intracellular calcium may cause delayed after-depolarizations, which may result in premature contractions & trigger arrhythmias

  • Digoxin has a narrow therapeutic window & the following factors can affect concentrations or enhance toxicity: 

    • Renal impairment

    • Hypovolemia

    • Hypokalemia

    • Hypomagnesemia

    • Hypernatremia

    • Acidosis

    • Drug interaction

    • Poisoning/ingestion

    • MI

  • ECG findings are: 

    • ↑ PR 

    • ↓ QTc

    • ST segment depression 

    • Diminished amplitude or inversion of T waves

 

 

Considerations 

 

  • Medical emergency that needs consultation with toxicology & cardiology 

  • Need for monitoring (ICU/high acuity unit) 

  • Cardiac arrhythmias which may be lethal:

    • Ectopy & tachycardia: PVCs, bigeminy, VT, VF

    • Cardiac arrest from asystole, VF (usually fatal)

    • Bradyarrhythmia from ↑ vagal tone

      • AV junctional & heart blocks 

 

 

Treatment 

 

  • Admit to monitored unit 

  • Consult toxicology & cardiology

  • Draw digoxin level

  • Antidote = digibind (Fab)

    • Dosing:

      • Known ingested digoxin dose: give 2 vials of Fab for every mg of digoxin ingested

      • Chronic toxicity or dose unknown, calculate # of vials as per this formula:

        • serum digoxin concentration (ng/ml) X weight (kg)/100 

      • If can't wait for serum levels or life-threatening toxicity: give 10-20 vials 

    • Hyperkalemia is common with digitalis toxicity, but do not treat with K+ lowering agents as digibind on its own will lower K+ & any more correcting can cause hypokalemia (which worsens digoxin toxicity) 

  • Volume resuscitation if hypotension 

  • Replace K+ & Mg as necessary 

  • Arrhythmias: follow standard ACLS algorithms

  • Avoid calcium even if hyperkalemic because patients have intracellular hypercalcemia & can worsen situation 

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