Absorption and metabolism in man of 16-epi-gitoxin, a new semi-synthetic cardioactive glycoside.

The pharmacokinetics of 3H-16-epi-gitoxin have been investigated after oral administration: The peak serum level occurred after 30-60 min, and its subsequent decline was in two phases with half-lives of 3.5 and 19.5 h, respectively. Within 3 days 66-70% of the administered radioactivity were eliminated by renal excretion. In the first 16 h 15% of excreted activity was in metabolites, but thereafter the glycoside was excreted in unchanged form. The metabolites were characterized by thin-layer chromatography and radio-scanning; it is assumed that they correspond to the bis- and monodigitoxosides as well as to the genin of 16-epi-gitoxin. The unusual pharmacokinetics of the glycoside are discussed in relation to its special kinetics at the molecular level, i.e. the rapid dissociation rate of the glycoside-(Na+ + K+)-ATPase-complex.