Digoxin Toxicity
Background
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Digoxin works by ultimately ↑ cardiac myocyte Ca+
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Excessive intracellular calcium may cause delayed after-depolarizations, which may result in premature contractions & trigger arrhythmias
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Digoxin has a narrow therapeutic window & the following factors can affect concentrations or enhance toxicity:
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Renal impairment
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Hypovolemia
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Hypokalemia
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Hypomagnesemia
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Hypernatremia
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Acidosis
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Drug interaction
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Poisoning/ingestion
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MI
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ECG findings are:
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↑ PR
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↓ QTc
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ST segment depression
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Diminished amplitude or inversion of T waves
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Considerations
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Medical emergency that needs consultation with toxicology & cardiology
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Need for monitoring (ICU/high acuity unit)
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Cardiac arrhythmias which may be lethal:
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Ectopy & tachycardia: PVCs, bigeminy, VT, VF
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Cardiac arrest from asystole, VF (usually fatal)
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Bradyarrhythmia from ↑ vagal tone
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AV junctional & heart blocks
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Treatment
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Admit to monitored unit
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Consult toxicology & cardiology
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Draw digoxin level
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Antidote = digibind (Fab)
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Dosing:
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Known ingested digoxin dose: give 2 vials of Fab for every mg of digoxin ingested
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Chronic toxicity or dose unknown, calculate # of vials as per this formula:
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serum digoxin concentration (ng/ml) X weight (kg)/100
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If can't wait for serum levels or life-threatening toxicity: give 10-20 vials
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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)
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Volume resuscitation if hypotension
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Replace K+ & Mg as necessary
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Arrhythmias: follow standard ACLS algorithms
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Avoid calcium even if hyperkalemic because patients have intracellular hypercalcemia & can worsen situation