Digoxin toxicity

Background

• Positive inotropic effect
  • Inhibits Na-K pump -> increased intracellular Na -> increased intracellular Ca
• Increases vagal tone
• Decreases refractory time; increases automaticity
  • Increases risk of dysrhythmias
• Renally cleared
• Hemodialysis does not work

AV block

RISK FACTORS

• Hypokalemia
• Hypovolemia
• Hypoxia
• cardiac ischemia
• renal insufficiency
• Meds
  • CCBs, amiodarone

Work-Up

• Dig level
  • Normal = 0.8-2 ng/mL
    • May have toxicity even with "therapeutic" levels
  • Measure serum level at least 6 hours after acute ingestion, immediately for chronic ingestion
    • If measure before this may be falsely elevated due to incomplete drug distribution
• Chemistry
  • Hyperkalemia level correlates with degree of toxicity
    • Hyperkalemia does not cause death; lowering K+ does not reduce mortality
  • Hypokalemia increases susceptibility in chronic toxicity
  • Hypomagnesemia is common
• Cr/BUN
• Urine output
• ECG (serial)

Clinical Manifestations

Cardiac

• Any type of dysrhythmia is possible except for rapidly conducted atrial arrhythmias
• Most common:
  • PVCs
  • Bradycardia
• Digitalis Effect
  • T wave changes
  • QT interval shortening
  • Scooped ST segments with depression in lateral leads

GI

• Nausea/vomiting
• Abdominal pain

Neuro

• Confusion
• Weakness
• Visual disturbances
  • yellow halos
  • Scotomas
• Delirium

Treatment

• Fab fragment Therapy
  • Acute Ingestion
    • 1 vial binds 0.5mg of digoxin
    • Adult dose
      • 10 vials over 30 minutes through 0.22 micron filter
    • Peds dose
      • 5 vials

• Activated charcoal 1g/kg (max 50g)
  • Only an adjunctive tx; NOT an alternative to fab fragment therapy
  • Consider only if present within 2 hr of ingestion

• Hyperkalemia
  • Do not treat! Do not give calcium!
    • Once fab is given hyperkalemia will rapidly correct
      • Aggressive tx with potassium-lowering agents could cause sig hypokalemia following therapy

• Hypokalemia
  • Treat!

• Hypomagnesemia
  • Treat

• Bradycardia
  • Atropine 0.5mg IV
• Hypotension
• Fluid

Indications for Rx of rhythm disturbances

    -hemodynamic compromise caused by bradycardia or tachycardia

    -frequent/complex ventricular ectopy

Bradycardia

    -Atropine

    -Electrical pacing

    -K contraindicated UNLESS severe hypok*

         -if tachycardic, give K*

         -if bradycardic, can worsen with K*

Tachyarrhythmias, increased automaticity

    -K

    -Mag

    -Lidocaine

    -Phenytoin

    -Cardioversion

Digoxin immune Fab

    -Ab bind to dig, remove drug from serum and myocardium

    -Ab-dig complex excreted in the urine

Indications

• Severe rhythm disturbances refractory to conventional therapy
• End-organ dysfunction
• Hyperkalemia >5 after acute overdose
• Pacemaker (may mask cardiac dysrhythmia)
• Consider for:
  • Dig level > 10 in acute ingestion
  • Dig level > 4 in chronic ingestion
  • If adult acutely ingests > 10mg
  • If child acutely ingests > 4mg

    -co-ingestion of cardiotoxic drugs: CCBs, beta-blockers, or TCAs

Empiric Dosages

-Chronic toxicity and unkown level: 4-6 vials (1/2 vial in child)

-Cariac arrest = 20 vials undiluted by IV bolus

Calculated Dosages: see package insert

-1 vial (40mg) binds 0.6mg dig

-Dose (vials) = body load (mg)/0.6 (mg/vial)

     -dig body load estimated from ingested dose or serum level

    -(dig level x wt in kg)/ 100 = # of vials

Kinetics

-Onset: 20mins

-Full effect: 90mins

• • Note** digitalis level unreliable after digibind administration, must follow patient clinically

Complications

-potential allergic reactions

-w/d of dig effect:

    -CHF

    -hypoK

    -dig levels not usable

Source

Rosen's, UpToDate