Antidote: digoxin immune Fab
Introduction
Digoxin-specific immune antibody fragments (digoxin immune Fab) bind digoxin in the circulation and remove it from its site of action, the sodium-potassium adenosine triphosphatase (ATPase) pump. One vial of digoxin immune Fab contains 40 mg of antibody fragments that bind approximately 0.5 mg of digoxin1.
Digoxin immune Fab is indicated for potentially lethal digoxin poisoning that is suggested by:
- cardiac arrest
- ventricular arrhythmias or runs of ventricular ectopic complexes
- bradyarrhythmias with associated hypotension
- severe hyperkalaemia (serum potassium concentration more than 6 mmol/L).
The dose of digoxin immune Fab depends on whether or not the patient is in cardiac arrest. For patients who are not in cardiac arrest, evidence suggests it is best to titrate digoxin immune Fab to clinical effect by giving 2 vials initially and repeating the dose if toxic effects recur—see Patient not in cardiac arrest. For patients in cardiac arrest, 5 vials are recommended initially—see Patient in cardiac arrest.
Useful clinical end points for assessing response to digoxin immune Fab are:
- restoration of adequate perfusion (guided by heart rate and blood pressure)
- serum potassium concentration of less than 6 mmol/L.
Formulae to calculate the dose of digoxin immune Fab overestimate the amount required and are not recommended.
Patient not in cardiac arrest
For an adult or child who is not in cardiac arrest, but has a life-threatening arrhythmia or severe hyperkalaemia (serum potassium concentration more than 6 mmol/L) due to digoxin poisoning, use:
digoxin immune Fab 80 mg (2 vials) intravenously, over 30 minutes2. If there is no response to the first dose, seek advice from a clinical toxicologist. If there is only partial response to the first dose, repeat the dose 30 minutes after the first dose. acute digoxin poisoning
Monitor the patient for 12 hours after administering digoxin immune Fab. Serum free digoxin concentration may rise as digoxin is mobilised from the tissues leading to rebound toxicity. If toxic effects (life-threatening arrhythmia or severe hyperkalaemia) recur, for an adult or child, use:
digoxin immune Fab 40 to 80 mg (1 to 2 vials) intravenously, over 30 minutes2.
Patient in cardiac arrest
For an adult or child with acute digoxin poisoning who is in cardiac arrest, follow advanced life support protocols3 and use:
digoxin immune Fab 200 mg (5 vials) intravenously, as a rapid injection4. If there is no response, seek advice from a clinical toxicologist.