Digoxin toxicity

Background

• Positive inotropic effect
  • Inhibits Na-K pump -> incr extracelluar K, incr intracellular Na -> incr intracellular Ca
• Increases vagal tone
  • Can lead to bradyarrhythmias (esp in young)
• Increases automaticity
  • Can lead to tachyarrhythmias (esp in elderly)
• Renally cleared
• Hemodialysis does not work
• 1 fab vial binds 0.5mg of digoxin

Risk Factors

1. Electrolyte Imbalance
   1. Hypokalemia, hypomagnesemia, Hypercalcemia
2. Hypovolemia
3. Renal insufficiency
4. Cardiac ischemia
5. Hypothyroidism
6. Meds
   1. CCBs, amiodarone

Clinical Manifestations

Cardiac

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

GI

1. Nausea/vomiting
2. Abdominal pain

Neuro

1. Confusion
2. Weakness
3. Visual disturbances
   1. Yellow halos
   2. Scotomas
4. Delirium

Work-Up

1. Dig level
   1. Normal = 0.8-2 ng/mL (ideal = 0.7-1.1)
      1. May have toxicity even with "therapeutic" levels
   2. Measure serum level at least 6 hours after acute ingestion (if stable), immediately for chronic ingestion
      1. If measure before this may be falsely elevated due to incomplete drug distribution
2. Chemistry
   1. Hyperkalemia level correlates with degree of toxicity
   2. Hypokalemia increases susceptibility in chronic toxicity
   3. Hypomagnesemia is common
3. Cr/BUN
4. Urine output
5. ECG (serial)

Treatment

See Digoxin Immune Fab

Activated Charcoal

1. Questionable efficacy
2. Only an adjunctive tx; NOT an alternative to fab fragment therapy
3. Consider only if present within 1 hr of ingestion
4. 1g/kg (max 50g)

Rhythm Disturbances

1. Fab fragments is the agent of choice for all dysrhythmias!
2. Bradyarrhythmias (symptomatic)
   1. Atropine 0.5mg IV
   2. Pacing
3. Tachyarrhythmias
   1. Lidocaine
      1. 1-3mg/kg over several minutes, followed by 1-4mg/min
   2. Phenytoin
      1. May enhance AV conduction
      2. Infuse at 25-50 mg/min to a loading dose of 10-15mg/kg
4. Cardioversion
   1. Consider lower energy settings (25-50J)

Hyperkalemia

1. Treat with Fab, not with usual meds
   1. Once fab is given hyperkalemia will rapidly correct
   2. Aggressive tx with potassium-lowering agents could cause sig hypokalemia following therapy
2. If Fab is not available and hyperkalemia is life-threatening then treat
3. Calcium is controversial (some say dangerous, others say not)

Hypokalemia

1. Chronic intoxication
   1. Raise level to 3.5-4
2. Acute intoxication
   1. Do not treat (likely that potassium level is rapidly rising)

Hypomagnesemia

1. Treat with 1-2g over 10-20 min
   1. Monitor for resp depresion
   2. Avoid in pts with:
      1. Renal failure
      2. Bradydysrhythmias/conduction blocks

See Also

• Digoxin Immune Fab
• Toxidromes

Source

Rosen's