Serum digoxin levels using an 125I-labelled antigen: Validation of method and observations on cardiac patients

1. Determinations of serum digoxin levels utilizing commercially available kits with an 125I-labelled antigen were precise and not materially different from results obtained with a 3H-labelled antigen. 2. In order to approximate the steady state level, serum digoxin levels should be drawn either before or at least six hours following the administration of an oral tablet. 3. Concomitantly given thiazide diuretics did not interfere with the absorption of a tablet of digoxin. 4. In the digitalized patient, slow alterations in serum levels after oral administration appeared well correlated with, at least, the negative chronotropic effects of the drug. 5. Maximal exercise testing, a maneuver often applied to cardiac patients, does not significantly alter the serum digoxin level.