Monday November 12, 2007
Scenario; 62 year old male with long history of atrial fibrillation and chronically on Digoxin admitted with dizzyness and found to have 3rd degree AV block. Patient is hemodynamically stable. Patient informed you that about a year ago, he had similar episode and was found to have high digoxin level and was treated with "antidote of digoxin". Later his digoxin dose was decreased by his cardiologist. You assume "Dig toxicity" and indeed Dig. level reported as 3.4 micrograms/ml. You ordered "Digibind". What step you should take in view of history of previously received "digibind" ?
Answer: Skin allergy test for digoxin immune Fab.
Since allergy testing can delay urgently needed therapy, it is not absolutely required before treatment of life-threatening digitalis toxicity with digoxin immune Fab (ovine), but should be considered if situation permits, particularly with previous history.
Skin testing should be considered for high risk individuals with history of multiple allergies, patients who previously treated with digoxin immune Fab. and patients with allergy to papaya extracts. Papain is used to cleave the whole antibody into Fab and Fc fragments, and traces of papain or inactivated papain residues may be present in digoxin immune Fab (ovine).
One should consider the possibility of anaphylactic, hypersensitivity or febrile reactions to digoxin immune Fab (ovine), even with first dose.
How to perform: Diluting 0.1 mL of reconstituted Digibind (9.5 mg/mL) in 9.9 mL sterile isotonic saline (1:100 dilution, 95 µg/mL). Injecting 0.1 mL of the 1:100 dilution (9.5 µg) intradermally and observing for an urticarial wheal surrounded by a zone of erythema. The test should be read at 20 minutes.
If skin testing causes a systemic reaction, a tourniquet should be applied above the site of testing. In case of full blown anaphylactic, hypersensitivity or febrile reactions to digoxin immune Fab (ovine) on test dose or infusion, the drug infusion should be discontinued and appropriate therapy initiated using oxygen, volume expansion, diphenhydramine, corticosteroids and airway management as indicated. Epinephrine should be use very cautiously and only if needed due to higher risk of arrthymias in the setting of digitalis toxicity.
