The elimination of tritiated doxycycline in normal subjects and in patients with severely impaired renal function.

Tritiated doxycycline was administered to four normals, four patients with renal failure interdialysis, and three patients in renal failure who were not on dialysis. Elimination was followed by collection of urine and feces up to eight days. It was demonstrated that renal failure reduced the urinary excretion of doxycycline. In normal individuals the total of 86% of the radioactivity was eliminated in five days, half in the urine and half in the feces. In patients, with renal failure on dialysis, 32% of the radioactivity was eliminated in that time, 9.3% in the urine and 23% in the feces. In renal failure patients not on dialysis 49% was eliminated in that time, 4% in the urine and 45% in the feces; when followed up to eight days a total of almost 70% of the radioactivity was eliminated and the increase elimination was accounted for by fecal elimination such that 64% was eliminated in the feces and 5% in the urine. The disappearance from the plasma compartment in all three groups was similar. Thus, although the plasma half-life of doxycycline is not significantly prolonged in renal failure, it appears likely that the drug is taken up into a compartment from which it may slowly be eliminated and when followed for a continual period of time a significant percentage can be recovered from the feces. There remains however, up to 30% of the administered dose which was not recovered and it must be assumed that a significant per cent of doxycycline would accumulate in a compartment, as yet unidentified, in patients with renal failure.