The Biotransformation of Cyclophosphamide in Man: Analysis of the Variation in Normal Subjects

Abstract

The metabolism of cyclophosphamide was studied in 40 subjects aged 33‐84, mean 64 years. After the intravenous injection of 14 C‐cyclophosphamide the radioactivity of the plasma and urine samples was analysed as regards unchanged cyclophosphamide and its metabolites. The parameters of the metabolism, half‐life of cyclophosphamide in the serum, peak and integrated serum concentration of the metabolites, distribution volume of injected radioactivity and the rate of excretion of cyclophosphamide and metabolites in the urine all exhibited a very large interindividual variation of a factor of 3‐10. Spontaneous intra‐individual variation, however, studied in 9 subjects, did not exceed that due to inaccuracy of the analysis. The possible clinical implications of these results are discussed.