UMEM Educational Pearls

Category: Toxicology

Title: Lily of the Valley, Part 2

Keywords: Digoxin, Cardioactive Steroids, Digitoxin, Digoxin-specific Fab Fragments (PubMed Search)

Posted: 11/7/2014 by Kishan Kapadia, DO
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Digoxin-specific antibodies are produced in immunized sheep and have high binding affinity for digoxin and, to a lesser extent, digitoxin and other cardiac glycosides. The Fab fragment binds free digoxin and once the digoxin-Fab complex is formed, the digoxin molecule is no longer pharmacologically active.  The complex is renally eliminated and has a half-life of 14-20 hours (may increase 10-fold with renal impairment).  Reversal of signs of digoxin/digitalis intoxication usually occurs within 30-60 minutes, with complete reversal varying up to 24 hours.

Contraindication: None known.  Caution is warranted in patients with known sensitivity ot ovine (sheep) products.  Product may contain traces of papain and caution advised in patients with allergies to papain, papaya extracts, chymopapain.

Adverse effects

1) Monitor for potential hypersensitivity reactions and serum sickness

2) In patients with renal insufficiency and impaired renal clearance of dig-Fab complex, a delayed rebound of free serum digoxin levels may occur

3) Removal of the effect of digoxin/digitalis may exacerbate preexisting heart failure

4) Removal of digoxin/digitalis effect may cause hypokalemia

Laboratory interaction: Digoxin-Fab complex cross-reacts with the antibody commonly utilized in quantitative immunoassay techniques.  This results in falsely high serum concentrations of digoxin due to measurement of the inactive Fab complex.  Therefore, measure free digoxin levels, which may be useful for patients with renal impairment.

Dosing: Each vial of Fab product binds 0.5 mg of digoxin.

Digoxin-specific Fab (round up vial calculation)

# of vials = Digoxin concentration (ng/mL) x Pt Wt (kg)