title: Cross-reactivity of TDX and OPUS immunoassay systems for serum digoxin determination.
abstract: The properties of the widely used TDX Analyzer and recently developed OPUS Immunoassay System were compared using 403 serum specimens taken from patients who did or did not take digoxin. Of the 210 specimens from patients not treated with digoxin, a false- positive digoxin concentration was detected in 15 specimens (7%) by TDX and in only 2 specimens (1%) by OPUS because of the cross-reactivity with structurally similar drugs. Potassium canrenoate, digitoxin, deslanoside, and methyldigoxin exhibited marked concentration-dependent cross-reactivity in the TDX assay method, whereas deslanoside and methyldigoxin only showed cross-reactivity with the antibody used in the OPUS method. Although a poor correlation was observed between these two methods for the determination of 193 samples from patients treated with digoxin, the correlation was remarkably improved (r = 0.914) and the slope approximated unity when excluded the data from patients who were treated concurrently with the cross-reactive compounds. In routine TDM of digoxin, the authors experienced two cases in which cross-reactivity of the assay system caused a clinical problem. Concurrent administration of intravenous canrenoate apparently interfered with the digoxin assay by TDX, but this problem was solved by using the OPUS system. The authors found OPUS more useful for monitoring serum digoxin concentrations in patients because of its superior specificity.
authors.affiliation: Department of Hospital Pharmacy, School of Medicine, Kobe University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Okazaki
authors.forename: Y
authors.initials: Y
authors.lastname: Tanigawara
authors.forename: T
authors.initials: T
authors.lastname: Kita
authors.forename: F
authors.initials: F
authors.lastname: Komada
authors.forename: K
authors.initials: K
authors.lastname: Okumura
mesh_terms: D000889:Anti-Arrhythmia Agents / Q000097:blood*; D002191:Canrenoic Acid / Q000008:administration & dosage; D003429:Cross Reactions; D004077:Digoxin / Q000097:blood*; D004347:Drug Interactions; D016903:Drug Monitoring / Q000379:methods*; D006801:Humans; D007118:Immunoassay / Q000379:methods; D000451:Mineralocorticoid Receptor Antagonists / Q000008:administration & dosage; D011933:Reagent Kits, Diagnostic
chemical_list: D000889:Anti-Arrhythmia Agents; D000451:Mineralocorticoid Receptor Antagonists; D011933:Reagent Kits, Diagnostic; D004077:Digoxin; D002191:Canrenoic Acid