Pharmacology · Specific antidotes
Digoxin immune Fab !
Antibody fragments made in sheep that bind digoxin in the blood and pull it off the sodium pump. The specific antidote for severe digoxin poisoning.
Updated 2026-11-01
Also called: Digoxin-specific antibody fragments, digitalis antitoxin
The figure shows digoxin held by the Fab of the mouse monoclonal antibody 26-10; the antidote is a different, sheep-derived Fab with the same idea.
Mechanism of action
The Fab fragments bind free digoxin with an affinity higher than the drug's own affinity for the Na⁺/K⁺-ATPase. Free digoxin falls, digoxin leaves the pump, and the pump works again: arrhythmias settle and potassium moves back into cells. The digoxin–Fab complex is then cleared by the kidneys.
- Fab binds free digoxin in the blood
- Digoxin comes off the Na⁺/K⁺ pump
- The pump restarts: rhythm improves, K⁺ re-enters cells
- The kidneys clear the digoxin–Fab complex
Pharmacokinetics
- Distribution
- Mostly in the blood and extracellular space
- Elimination
- By the kidneys together with the bound digoxin; slower in kidney failure, when toxicity can recur
- Onset and duration
- Symptoms usually improve within 30 to 60 minutes
Indications
- Life-threatening arrhythmias from digoxin (ventricular arrhythmias, progressive bradycardia, high-grade AV block), whatever the serum level
- Severe hyperkalaemia in acute digoxin poisoning
- Poisoning by other cardiac glycosides, such as digitoxin or oleander, though cross-reactivity is incomplete
Adverse effects
Common
- Worsening heart failure as digoxin's inotropic effect is lost
- Hypokalaemia, often within hours
Contraindications
- No absolute contraindications; allergy to sheep proteins is a relative contraindication
Key interactions
- Potassium replacement
- Potassium can fall quickly once the pump restarts, so it is replaced only as needed
What is monitored
- Continuous ECG
- Serum potassium, frequently in the first hours
- Kidney function
- Signs of heart failure and ventricular rate
Administration and safety
- Reconstituted and given intravenously, usually as an infusion; as a bolus in imminent cardiac arrest
- The amount is calculated from the dose ingested or the serum level; the number of vials is checked twice
- A serum digoxin sample is drawn before the first dose
Nursing care
- Draw digoxin and potassium levels before giving it
- Keep the patient on cardiac monitoring with resuscitation equipment at hand
- Ask about allergy to sheep proteins
- Teach the patient to report rash, fever or joint pain in the following days
Test yourself
Think of the answer, then tap the question to see it.
How does digoxin immune Fab reverse toxicity?
It binds free digoxin more tightly than the Na⁺/K⁺-ATPase does, so digoxin leaves the pump.
Why can potassium fall after the antidote?
The pump restarts and moves potassium back into cells.
Can digoxin Fab help in poisoning by plant cardiac glycosides?
Yes, it can be tried (for example oleander), but cross-reactivity is incomplete and more may be needed.
Related drugs
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Guía para el Manejo de Emergencias Toxicológicas (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 58 (McGraw Hill, 2025); DailyMed - DIGOXIN tablet (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); RCSB PDB - 1IGJ: 26-10 FAB:DIGOXIN COMPLEX-AFFINITY AND SPECIFICITY DUE TO SURFACE COMPLEMENTARITY (RCSB Protein Data Bank, 2026).
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Representative model, for educational purposes only.