Digoxin Toxicity

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Check local/national poisons advice. Establish where to get stocks of Digoxin immune FAB as they are expensive and so local stocks may be poor. Hyperkalaemia is a useful sign of severe Digoxin toxicity

About

• Used therapeutically but also found in the following plants: foxglove, oleander, lily of the valley.

Aetiology

• Digoxin blocks the Na/K ATPase pump which indirectly increases intracellular calcium.
• Decreases AV conduction and can cause bradycardia.
• Increases vagal tone. Also increases automaticity.
• Lethal dose can be as little as 10 times daily dose (Adult 10 mg, child 4 mg)
• Well absorbed orally. Half-life 30-40 hours.
• Peak toxicity 6 hours and death 6-12 hours post-ingestion.
• Causes Hyperkalaemia

Factors that increase toxicity

• Low K, Low Mg, High Ca
• Amiodarone - altered protein binding
• Calcium channel blockers

Clinical

• Anorexia, Nausea and vomiting. Yellow vision.
• Diarrhoea, Abdominal pain
• Bradycardias, AV block, SVT (with AV block), AF, VT and even VF.

Investigations

• FBC, U&E, Digoxin level at 4 hours.
• ECG. Hyperkalaemia suggests Digoxin toxicity
• Serial ECGS. CCU Monitoring.

Management:Avoid Calcium chloride or gluconate.

• CCU monitoring. Can lead to hypotension, arrhythmias, cardiac arrest.
• Consider gastric lavage if seen within 1 hour and/or give activated charcoal if within 1 hour of ingestion in a cooperative patient. Repeated dosing may be helpful.
• Main reversal therapy is to give Digoxin immune FAB known as Digibind and DigiFab. In a cardiac arrest continue giving multiple vials of this for up to 30 minutes as resuscitation continues.
• Manage hyperkalaemia with Sodium Bicarbonate and/or Insulin/Dextrose.
• Avoid Calcium chloride or gluconate.
• Give Atropine 0.6 mg IV for AV block.
• Give Magnesium and consider Lidocaine 50-100 mg IV for refractory VT/VF.

Digoxin Immune Fab

• This is suggested where adult dose > 10 mg ingested, serious life threatening arrhythmias, Digoxin level > 15 nmol/ml (12 ng/ml), K > 5 mmol/l.
• Note Each Digibind vial will bind approximately 0.5 mg of Digoxin (or digitoxin) so multiple vials will need to be given in a significant overdose e.g. 10 mg Digoxin taken. You will have to summon as much as possible e.g. 20 vials.
• A potassium over 5.5 mmol/l suggests a lethal overdose unless Digoxin immune Fab is given. It is expensive and not always stocked. Contact poisons advisory for nearest stores.
• If there is renal failure then plasmapheresis may be needed to clear Digoxin Fab complexes.

Arrhythmia management

• If there is profound bradycardia then temporary pacing may be needed
• Anecdotally Ventricular tachycardia in the presence of Digoxin toxicity may respond to phenytoin and magnesium sulphate. If defibrillation is necessary then 25 J may be all that is required. Higher defibrillation energies may induce ventricular fibrillation.