The metabolism of cyclophosphamide. Dose dependency and the effect of long-term treatment with cyclophosphamide.

Studies on the metabolism of cyclophosphamide-14C were performed in 10 subjects at different single dose levels within the range of 0.02-10 mg/kg body-weight and in five subjects before and following an average 22 days treatment with cyclophosphamide in daily doses of 2 mg/kg. The parameters of cyclophosphamide metabolism--serum half-life of unchanged cyclophosphamide, serum concentration of metabolites, and rates of excretion of cyclophosphamide and metabolites in the urine--were all independent of dose. No change of the metabolism was demonstrated after treatment with cyclophosphamide for 22 days.