Tissue concentration and turnover of tritiated digoxin in dogs

Abstract

Thirty-four dogs were given tritium-labeled digoxin intravenously. Serum and tissue concentrations and half-times were determined. As demonstrated previously in human subjects, digoxin has selective affinity for cardiac muscle. The mean digoxin half-time was 23 hr. in the serum and 26 in heart muscle, demonstrating that the serum digoxin concentration and its disappearance bears a direct relation to the cardiac concentration and disappearance of digoxin. Considerable amounts of digoxin were also demonstrated in kidney, pancreas and liver. The half-times in these and other tissues were also similar to the serum half-time. Brain tissue revealed only barely detectable levels of digoxin and a blood-brain barrier for digoxin is proposed.The similarity of the organ distribution of tritiated digoxin in dogs and human subjects is noted and suggests that the serum half-time of tritiated digoxin may be used as an index of release of digoxin from cardiac muscle in the human, and correspondingly, its therapeutic activity.A high mean heart to serum digoxin ratio of 42.5:1 (range 35–58:1) was demonstrated after the serum plateau was reached, suggesting the possible value of a serum digoxin determination in the clinical assessment of myocardial digoxin content.