A solid phase radioimmunoassay for digoxin and its acylated derivatives.

A solid phase radioimmunoassay (RIA) is presented for the determination of digoxin and its acylated derivatives. In the procedure the antiserum is covalently bound to bromacetylcellulose. Therefore the free and the immunologically bound digoxin fractions can easily be separated by centrifuging. The radioactivity in the supernatant representing the unbound digoxin is proportional to the digoxin concentration in the sample. This modification of the RIA for digoxin is far more time saving than the separation procedure using dextran-coated charcoal as an absorbent; nevertheless both methods are equally sensitive, specific and reliable. The use of the solid phase assay is demonstrated comparing the bioavailability of various digoxin derivatives.