Tritiated digoxin: studies in renal disease in human subjects

Digoxin is excreted primarily in the urine as the unchanged glycoside: 60-80% can be recovered from the urine in 7 days after a single intravenous dose in the human subject. Definition of the role of the kidney in digoxin excretion, turnover and metabolism was studied in 57 patients with renal disease, transplant candidates and/or donors and recipients of renal transplants. A single dose of 3H digoxin was given to the subjects, frequent serum samples were obtained and all urine and stools were saved for 7 days. All specimens were extracted with chloroform and digoxin, and its metabolites were separated by column chromatography. Results reveal that the serum T1/2 and the dominant T1/2 of digoxin are prolonged in renal disease in direct proportion to the reduction in creatinine clearance (r = 0.833). The blood urea nitrogen (BUN) is also related to digoxin clearance (r = 0.742). The higher the BUN, the less digoxin excreted in the urine. Anephric patients excrete more digoxin in stool, but this does not compensate for the lack of renal excretion. Transplanted kidneys excrete digoxin in proportion to renal functional capacity, as do patients who have experienced unilateral nephrectomy. Peritoneal or hemodialysis is not effective in removing digoxin from the human subject and may lead to digitalis intoxication if K+ is allowed to fall to critical levels. Digoxin excretion is not volume related, as patients with nephritogenic diabetes insipidus excrete the drug normally with urine volumes of 12 liters a day. Digoxin doses in renal insufficiency should be dictated by knowledge of renal functional ability of the kidneys and after "normal" loading doses, and maintenance doses should be 1/4 to 1/2 those usually administered.