[Digoxin concentration in blood].

Abstract

Immunoreactive digoxin-like activity was found in the Chinese medicine, KYUSHIN tablet, taken popularly in Japan without prescription. The antibodies used in the assays of digoxin reacted with Ch'an-su, the major effective component of KYUSHIN, which contained cardiotonic steroids with a chemical structure similar to that of digoxin. One tablet of KYUSHIN had digoxin-like immunoreactivity equivalent to 1.9 micrograms. (TDx analyzer), 1.5 micrograms (Du Pont aca analyzer) and 72 micrograms digoxin (Enzymun-Test, Boehringer). These different equivalencies may be attributed to differences in cross-reactivity of the antibody used in the immunoassays. Two healthy volunteers took two KYUSHIN tablets three times a day, a typical dose, and digoxin-like immunoreactivity reached almost 0.4 microgram/l in 0.5 day. Recently, a competitive digoxin chemiluminescent immunoassay has been developed by Ciba Corning ACS 180. The assay utilizes an acridinium-ester labelled mouse monoclonal digoxin antibody as the tracer. In the extracted solution of KYUSHIN and serum after administration of two tablets, the digoxin-like immunoreactivity value on the Ciba Corning ACS 180 digoxin assay was < 0.10 microgram/l (off-range low). Therapeutic drug monitoring should be interpreted carefully in patients taking Chinese medicines, many of which contain the Ch'an-su component.