Administration of Tritiated Digoxin with and without a Loading Dose

Abstract

The metabolism of digoxin was investigated in 8 normal subjects during daily administration of 0.5 mg of the drug for 1 to 2 weeks. Two dose schedules were used. One group was given 2.0 mg of tritiated digoxin whereas this loading dose was omitted in the other group. Serial blood samples and collection of total urine and stool were analyzed for radioactivity. The fraction of urine and stool which had the greatest amount of activity was further examined by paper chromatography. Absorption of an alcoholic solution of tritiated digoxin began within 30 minutes. A peak concentration of activity in blood was reached in 1 hour. Cumulation of digoxin occurred even though the initial loading dose was not given. By the sixth day, there was no statistical difference in the concentration of radioactivity in the blood between the 2 groups. The data are consistent with a daily excretion of digoxin In urine and stool of about 30% of that amount present in the body. Wtih subjects receiving 0.5 mg daily for more than 1 week, the total daily body accumulation was in the range of 1.2 mg. The implication of the present study for clinical practice is that the Initial loading dose is not necessary except when the maximum effect of the drug is needed within 1 to 2 days. If the full effect is not required within this time, the same effect may be obtained within a week by administering digoxin without the necessity of a loading dose.