Pharmacokinetics of dihydrodigitoxin in the cat. A comparison with digitoxin.

Pharmacokinetics of digitoxin (DGT) and its derivative hydrogenated at the unsaturated lactone ring have been studied using the 3H-labelled compounds in cats. Blood level data could be described by an open three compartment body model. The biological half-lives of dihydrodigitoxin (DH-DGT) and DGT are rather similar (0.12, 0.48, 20.4 h, and 0.11, 0.43, 31.8 h, respectively), whereas the volume of distribution of DH-DGT is about 1/10 from that of DGT (0.241 versus 2.581). Especially in myocardial tissue a significantly lower DH-DGT concentration was measured, indicating the loss of affinity to cardenolide binding sites by hydrogenation. Dihydrodigitoxinic acid was detected as the main metabolite of DH-DGT.