Studies on digitalis. IX. Some kinetic aspects of digitoxin metabolism.

The metabolic pattern of cardioactive and inactive conjugated metabolites (a maximum of 24 substances) was studied in one female and one male after a single dose of 0.6 mg digitoxin intravenously. Serum samples were obtained after 24 hr, and 24-hr urine was collected after 1, 2, 4, 6, and 8 days. With the methods used, enzymatic cleavage of conjugated bonds, thin-layer chromatography (TLC) separation, and a modified 86Rb method, the products of hydroxylation, hydrolysis, and conjugation could be separated. The Kendall rank correlation coefficient was used to compare the results from Subjects 1 and 2. Conjugation was the most rapid process, followed by hydrolysis and hydroxylation. Metabolism was progressive, leading to an increase in metabolites resulting from several enzymatic processes with time. Unchanged digitoxin reached minimum values on the fourth and sixth days and increased again on the eighth day. This indicated a continuous release of digitoxin from tissue stores and the enterohepatic circulation.