One-Hour Radioimmunoassay of Serum Drug Concentrations, as Exemplified by Digoxin and Gentamicin

Abstract

Double-antibody radioimmunoassays in which tritium is used for labeling have been adapted for emergency determinations of serum drug concentrations. In the cases of digoxin and gentamicin, the first and second antibody incubations may be carried on simultaneously, minimizing incubation times (10 and 27 min, respectively). Counting the bound radioactivity in solubilized immunospecific precipitates decreases variability in the composition of the phase counted and markedly decreases problems of quenching and chemiluminescence. Logitlog transformation of the sigmoidal standard curve results in a straight line, which can be described by its slope and intercept and which remains constant if assay conditions and critical reagents are held constant. Because the slope and intercept of the standard curve are characteristic of a given assay system, it is possible to calculate the theoretical standard curve for a specific assay system by using the means of previously observed slopes and intercepts. Thus, a separate standard curve need not be prepared for each subsequent assay run. Total time required for drug determinations is now less than 1 h. When unknown samples were measured by both the conventional radioimmunoassay method and the new rapid radioimmunoassay method, the values correlated well (r = 0.99) for both digoxin and gentamicin.