Pharmacokinetics of cyclophosphamide in renal failure

The metabolism of cyclophosphamide was determined in five patients with severe renal insufficiency. After the intravenous injection of 14-C-cyclophosphamide the activities due to unchanged cyclophosphamide and metabolites were determined in samples from urine and serum for 2-3 days. Only 22% of the injected radioactivity could be recovered in the urine during the first 3 days as against the normal of some 65% The rate of biotransformation seemed normal and in agreement with these findings a very long term retention of metabolites could be demonstrated. The clinical implications of these results are discussed.