[The monitoring of plasma digoxin levels during acute digitalis poisoning treated with Fab anti-digoxin fragments].

Life-threatening digitalis intoxication is treated using digoxin specific antibody fragments (Fab) that bind and inactivate the drug. The free digoxin serum concentration could be useful in the management of Fab-treated patients, but the standard methods of measurement can be clinically misleading because Fab anti-digoxin interferes with digitalis immunoassay measurements. A case involving Fab therapy of a digoxin overdosed patient, in which two laboratory methods gave very different results, is reported. The radioimmunologic assay (RIA), widely used in laboratories, yielded high values without relation to true serum free digoxin concentration. On the contrary, the recently introduced fluoroenzymatic sequential immunoassay (FEIA), which accurately measures free glycoside concentration, was a valuable aid in monitoring Fab treatment. Therefore, cardiologists' knowledge of a possible interference of specific anti-digoxin fragment treatment with many immunoassays may greatly enhance the rational management of these patients.