This ‘lesson of the week’ article in the BMJ discusses the use of digoxin specific antibody fragments (Digibind®) in the treatment of digoxin toxicity, and how care must be taken as they can interfere with digoxin immunoassay measurements.  

This point is illustrated by a case report - a 78-year old lady with complex medical history and multiple medications admitted with chest infection, acute on chronic renal failure (due to dehydration, nephrotoxins, and sepsis), complicated by digoxin toxicity (concentration of 4.8 nmol/L) causing bradycardia induced syncope and by traumatic fracture of the left ankle.

Her digoxin (and other medicines) was stopped and Digibind® was given. On day 2 of her admission, the biochemist informed the on-call medical team that the digoxin concentration was 7.4 nmol/l and a further dose of Digibind was given despite her clinical improvement.  She then developed atrial fibrillation with a rapid ventricular response requiring rate controlling treatment.  In this case the second dose was not indicated, as the digoxin concentration was falsely raised after the initial administration of Digibind.

The authors note that clinicians should be cautious when interpreting digoxin concentrations after administration of Digibind, and the use of a further dose should be guided by the patient’s symptoms rather than the digoxin level.  After digoxin specific antibody fragments have been given, restarting digoxin should be postponed until their effects have been eliminated; this may require several days (longer in patients with renal impairment).