Measurement of serum digitoxin in patients by radioimmunoassay using specific antiserum.

Digitoxin is used to treat patients with heart failure. A radioimmunoassay procedure for the specific determination for digitoxin in serum was developed using the antiserum (antiserum (A)) raised against digitoxin 3'-hemisuccinate-BSA conjugate. The intra- and interassay variability were <10% in the range of 5-100 ng/ml. The specificities of antiserum (A) and the commercial anti-digitoxin antiserum (antiserum (B)) were assessed by cross-reactivity studies with various related compounds. Antiserum (A) was highly specific for digitoxin. Mean digitoxin concentrations in serum samples (n=34) from digitalized patients by RIA using these antisera were 10.0 and 12.4 ng/ml, respectively. This RIA using antiserum (A) measure unmetabolized digitoxin and may be applicable for pharmacokinetic studies.