Falsely elevated serum digitoxin concentrations due to cross-reactivity ofwater-extractable digitoxin-like immunoreactivity of Chinese medicine ChanSU: elimination of interference by use of a chemiluminescent assay

Chinese medicines are available without prescription in health food stores. One such Chinese preparation, Chan SU, is used as a cardiotonic agent. Dig oxin-like immunoreactivity of Chan SU has been reported in the past. in thi s report we demonstrated significant digitoxin-like immunoreactivity of Cha n SU. For example, when a 20-mu l aliquot of an aqueous extract of Chan SU (2 mg/ml) was added to drug-free serum, the observed digitoxin-like immunor eactivity was 51.40 ng/ml by the fluorescence polarization assay. In contra st, a new chemiluminescent assay for digitoxin did not show any immunoreact ivity. When very small amount of aqueous extract of Chan SU was added into serum containing digitoxin, the observed digitoxin concentrations were fals ely elevated when measured by the fluorescence polarization immunoassay (FP IA) but did not change significantly when measured by the chemiluminescent immunoassay (CLIA), Significant digitoxin-like immunoreactivity was also ob served (FPIA) in mice after feeding with Chan SU. Because bufalin, cinobufo talin and cinobufugin are major components of Chan SU, digitoxin-like immun oreactivity of these purified compounds was also studied. Bufalin was ident ified as the major digitoxin-like immunoreactive compound responsible for m ost of the interference in serum digitoxin measurement using the FPIA. (C) 2000 Elsevier Science B.V. All rights reserved.