Abstract
Digitalis-like immunoreactive substances (DLISs) have been shown to cross-react with anti-digoxin antibodies. We previously reported that eplerenone, the structure of which is similar to that of digoxin,interfered with digoxin measurements in a fluorescence polarization immunoassay (FPIA), microparticle enzyme immunoassay (MEIA), and affinity column-mediated immunoassay (ACMIA),and also that the extent of interference was different in each assay. Digoxin has a narrow therapeutic window; therefore, it is important to measure its serum concentrations without interference by clinically co-administered drugs. In this study, we performed two additional types of assays (enzyme multiplied immunoassay technique (EMIT) and chemiluminescent immunoassay (CLIA)) to clarify cross-reactivity between eplerenone and anti-digoxin antibodies. Furthermore, we used EMIT and CLIA to measure apparent digoxin concentrations in mixed solutions of eplerenone (1-100 μg/mL) and digoxin (1-3 ng/mL). Eplerenone was not detected as digoxin by EMIT and CLIA in cross-reaction tests. Furthermore, the apparent concentration of digoxin when co-administered with eplerenone was not significantly affected in EMIT and CLIA. These results suggest that EMIT and CLIA may be able to accurately measure serum digoxin concentrations in patients adjunctively receiving eplerenone.
Key words: DLIS, eplerenone, EMIT, CLIA, therapeutic drug monitoring