The most commonly used preparation of digitalis is digoxin,which is obtained from the leaves of Digitalis lanata, a common flowering plant called "foxglove." Digitalis compounds are potent inhibitors of cellular Na ⁺ /K ⁺ -ATPase. The words digitalis and digoxin are widely used interchangeably.

When digoxin is taken in overdose; cardiac symptoms including sinus Bradycardia, sinoatrial arrest, 2 ^nd or 3 ^rd degree AV block and more rarely ventricular fibrillation or ventricular tachycardia may occur.Generally, levels need to be >2.0 ng/mL for significant adverse effects (therapeutic range 0.8-2.0 ng/mL) and typically is >5 ng/mL before life threatening adverse effects to occur.Vomiting is also a common adverse effect with digoxin toxicity.

The formulas provided can be utilized in 2 ways depending upon known items:

• If the amount of oral digoxin ingested is known; this enters one equation
• If the blood level of digoxin is known; a second equation is utilized

Notes to remember:

• Each vial of digoxin FAB neutralizes 0.5 mg of absorbed digoxin
• Oral formulations typically have 80% of the ingested amount absorbed
• The formulas provided calculate the amount to administer to theoretically neutralize the entire amount of digoxin; it should however be noted, that symptoms typically abate once levels are <2 ng/mL

Formula if amount ingested known:

Vials Dig FAB = 1.6*Digoxin ingested

• Digoxin ingested is in mg
• There are 2 vials needed per mg of absorbed digoxin
• 0.8 proportion of orally ingested digoxin is absorbed

Formula if blood concentration known:

Vials Dig FAB = 0.0112*Digoxin Conc*Weight

• Digoxin Conc = Digoxin Concentration in ng/ml
• 0.0112 is the multiple of 2 vials/mg * 5.6 (volume of distribution of digoxin), divided by 1000
• Weight is in kg

References

DigiFab ^TM (Digoxin Immune FAB (Ovine) FDA label.Available at http://www.fda.gov/CBER/label/digpro083101LB.pdf (last accessed 6 July 2008)

Jelliffe RW. An improved method of digoxin therapy. Ann Intern Med. 1968;69(4):703-17.

Jelliffe RW. Digitalis therapy: simple formulas to plan and adjust dosage regimens. MD Comput. 1984;2:36-43.

Jelliffe RW, et al. Reduction of digitalis toxicity by computer-assisted glycoside dosage regimes. Ann Intern Med 1972;77: 891-906.

Hurstig MJ, et al. Determination of Free Digoxin Concentrations in Serum for Monitoring Fab Treatment of Digoxin Overdose. Clin Chem. 1987;33(9):1652-5.