Digoxin toxicity

Background

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

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
  • 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

Neither amount ingested nor digoxin level are known:

• 1 vial binds 0.5mg of digoxin
• Adult dose
  • 10 vials over 30 minutes through 0.22 micron filter
• Peds dose
  • 5 vials
• Peak effect occurs after 90min, initial response after 20min
  • Repeat dose if clinical response is inadequate

Amount ingested is known but digoxin level is unknown

• Step 1: Calculate total body load (TBL)
  • TBL = dose (in mg) ingested
• Step 2: Calculate number of vials needed
  • Number of vials = TBL X 2 (round up to nearest whole number)

Steady state digoxin level is known

• Number of vials = (dig level(in ng/mL) X pt wt) / 100

Chronic toxicity without severe signs

• Give half the recommended dose
  • Otherwise may unmask the condition for which the pt is taking digoxin

• Fab side-effects
  • Allergic reaction
  • Withdrawal of dig effect:
    • CHF
  • Hypokalemia

• 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

• Rhythm Disturbance
  • Bradycardia (symptomatic)
    • Atropine 0.5mg IV
    • Pacing
  • Tachyarrhythmias
    • K
    • Mag
    • Lidocaine
    • Phenytoin
    • Cardioversion

Source

Rosen's, UpToDate