title: Digoxin immunoassay with cross-reactivity of digoxin metabolites proportional to their biological activity.
abstract: Our objective was to identify commercially available digoxin immunoassays whose cross-reactivity with digoxin metabolites paralleled the pharmacological activity of the metabolites. We measured the immunoreactivity of digoxigenin bis- and monodigitoxosides, digoxigenin, and dihydrodigoxin in four immunoassays and compared the immunoactivities with pharmacological activities from studies involving whole-animal and receptor (Na,K-ATPase)-based assays. Correlation coefficients for comparisons of immunoassay reactivity and human heart receptor reactivities were: ACS, 0.96; TDx, 0.60; Stratus, 0.57; and Magic, 0.42. Comparison with other biological assays showed a similar trend. The major difference in metabolite cross-reactivities among the immunoassays was that of digoxigenin (ACS, 0.7%; TDx, 103%; Stratus, 108%; Magic, 153%), which has approximately 10% bioactivity relative to digoxin. Measured recovery of mixtures of digoxin and metabolites confirmed these findings. We conclude that the monoclonal antibody in the ACS digoxin assay closely mimics Na,K-ATPase in detecting digoxin and its metabolites. This finding provides a basis for developing therapeutic drug monitoring immunoassays capable of approximating the true pharmacological activity of a mixture of drug metabolites.
authors.affiliation: Department of Pathology, University of Louisville School of Medicine, KY 40292.
authors.forename: J J
authors.initials: JJ
authors.lastname: Miller
authors.forename: R W
authors.initials: RW
authors.lastname: Straub
authors.forename: R
authors.initials: R
authors.lastname: Valdes
mesh_terms: D000818:Animals; D001681:Biological Assay; D002415:Cats; D004076:Digoxigenin / Q000031:analogs & derivatives / Q000097:blood / Q000494:pharmacology; D004077:Digoxin / Q000031:analogs & derivatives / Q000097:blood* / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects; D006801:Humans; D007118:Immunoassay / Q000706:statistics & numerical data*; D051379:Mice; D010042:Ouabain / Q000378:metabolism; D012680:Sensitivity and Specificity; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors
chemical_list: C023685:digoxigenin-bis(digitoxoside); C000967:dihydrodigoxin; C018046:digoxigenin-mono(digitoxoside); D010042:Ouabain; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase; D004076:Digoxigenin