All Pharmacy Pearls

Introduction

Digoxin is a cardioactive glycoside used for atrial flutter, atrial fibrillation, and heart failure. It inhibits the sodium/potassium ATPase pump in cardiac myocytes, increasing intracellular sodium and reducing sodium/calcium exchange. The resulting increase in intracellular calcium drives inotropy but can also produce life-threatening dysrhythmias when exposure becomes excessive.

Toxicity may present with premature ventricular contractions, biphasic T waves, shortened QT interval, or AV block. Serum concentrations are useful but must be interpreted clinically; toxicity can begin above 2 ng/mL, while therapeutic concentrations are commonly cited around 0.8-2 ng/mL.

Key Points

  • Digoxin poisoning can cause clinically important bradyarrhythmias, AV block, ventricular dysrhythmias, and electrolyte shifts.
  • Digoxin immune Fab is the targeted antidote for serious or life-threatening toxicity.
  • After Fab, total digoxin levels may appear falsely elevated; free digoxin concentrations are more clinically useful when available.
  • Monitor potassium closely because Fab treatment can shift potassium intracellularly and precipitate hypokalemia.

Digoxin Immune Fab

TopicPractical Detail
Vial ContentOne vial contains 40 mg and binds approximately 0.5 mg of digoxin.
Known Body LoadVials = total body load in mg x 2.
Unknown Acute ToxicityInitial empiric adult dose: 10 vials.
Chronic Unknown AmountAdults: 3-6 vials. Children: 1-2 vials.
AdministrationInfuse IV over 30 minutes. If cardiac arrest is imminent, bolus administration can be used.
CompatibilityUse 0.9% sodium chloride only.

Clinical Pearl

After Fab administration, total digoxin concentrations may rise because assays detect both free and bound drug. Follow clinical response, rhythm, potassium, and free digoxin concentrations when available.

Evidence Overview

SourceDesignPractical Takeaway
Antman 19904Open-label multicenter trial, n=150.Digoxin-specific Fab resolved or improved toxicity in 90% of patients; median dose was about 5 vials.
Renard 19975Pharmacokinetic study, n=16.Clearance decreased with renal function and age, but all patients recovered and no adverse effects were reported.
Ward 20009Healthy volunteer pharmacokinetic comparison.Both Fab products reduced free digoxin concentrations below assay detection; total concentrations increased from Fab-bound drug.
Wei 20218FAERS case report analysis, n=121.Serious adverse-event reports occurred with both products; hypotension, cardiac arrest, and death were among reported serious events.

Clinical Conclusions

Digoxin toxicity can be life-threatening. Treat unstable dysrhythmias, significant hyperkalemia, and serious poisoning as time-sensitive antidote scenarios.

For unknown acute ingestion, start with 10 vials. Chronic unknown exposures usually require fewer empiric vials.

Do not overread total levels after Fab. Bound drug can inflate total digoxin concentrations; clinical response and free concentrations are more useful.

Monitor potassium closely. Potassium may shift intracellularly after reversal, creating hypokalemia risk.

Full Reference List

  1. Bismuth C, Gaultier M, Conso F, Efthymiou ML. Hyperkalemia in acute digitalis poisoning. Clin Toxicol. 1973;6(2):153-162.
  2. David MNV, Shetty M. Digoxin. In: StatPearls. StatPearls Publishing; 2022.
  3. Lexicomp Online, Lexi-Drugs Online. Waltham, MA: UpToDate, Inc.; January 2023.
  4. Antman EM, et al. Treatment of 150 cases of life-threatening digitalis intoxication. Circulation. 1990;81(6):1744-1752.
  5. Renard C, Grene-Lerouge N, Beau N, Baud F, Scherrmann JM. Pharmacokinetics of digoxin-specific Fab. Br J Clin Pharmacol. 1997;44(2):135-138.
  6. Roberts DM, Gallapatthy G, Dunuwille A, Chan BS. Pharmacological treatment of cardiac glycoside poisoning. Br J Clin Pharmacol. 2016;81(3):488-495.
  7. Ujhelyi MR, Robert S. Pharmacokinetic aspects of digoxin-specific Fab therapy. Clin Pharmacokinet. 1995;28(6):483-493.
  8. Wei S, Niu MT, Dores GM. Adverse events associated with use of digoxin immune Fab. Drugs Real World Outcomes. 2021;8:253-262.
  9. Ward SB, Sjostrom L, Ujhelyi MR. Comparison of DigiTAb versus Digibind. Ther Drug Monit. 2000;22(5):599-607.
Tags: Digoxin Toxicology Digoxin Immune Fab Antidotes