Plasma digoxin: assay anomalies in Fab-treated patients

Using a variety of radioimmunoassay methods, plasma digoxin concentrations were measured in two patients before and after the administration of ovine Fab antibody fragments to remove the effects of digoxin. Gross method-dependent anomalies in the results due to in vitro drug interaction were observed. More widespread use of immunotherapy may invalidate data obtained by direct immunoassay techniques.