Reversal of lethal digoxin toxicity in guinea pigs using monoclonal antibodies and Fab fragments.

To extend the potential application of digoxin-specific immunoglobulin (Ig) (Fab) fragments for the reversal of advanced digitalis intoxication, monoclonal digoxin-specific antibodies were obtained by fusion of myeloma cell lines with spleen cells from mice immunized with a digoxin-serum albumin conjugate. The monoclonal antibody from the cell line designated Dig 26-10 had high affinity (KA = 5 X 10(9) M-1) and specificity for digoxin and was tested for its efficacy in the reversal of advanced, otherwise lethal digoxin toxicity in guinea pigs given a loading dose of 500 micrograms of digoxin per kg b.wt. i.v. followed by continuous infusion of digoxin at 10 (IgG-treated group) or 50 (Fab-treated group) microgram/kg/min. Control animals given nonspecific rabbit or mouse Igs after the onset of digoxin-toxic ventricular arrhythmias all died. Administration of monoclonal digoxin-specific antibody as intact IgG in doses stoichiometrically equivalent to the digoxin dose fully reversed digoxin toxicity in six of eight animals and prolonged survival somewhat in the remaining two animals. Fab fragments from the Dig 26-10 monoclonal antibody were even more effective, with rapid reversal (mean time 7 min) of all arrhythmias and survival of all animals so treated. We conclude that murine monoclonal antibodies and their Fab fragments are capable of reversing advanced and otherwise lethal digoxin-induced arrhythmias in a guinea-pig experimental model and offer potential advantages over polyclonal antibodies in the management of this clinically important problem.