Comparison of cytotoxic action of iphosphamide and cyclophosphamide.

We compared the cytotoxic effects of cyclophosphamide and iphosphamide on normal hematopoietic colony-forming units (NCFU) and L1210 leukemia colony-forming units (LCFU), using the quantitative spleen colony assay. Cyclophosphamide was more cytotoxic for NCFU than iphosphamide, but both agents had a similar cytotoxic effect on LCFU survival, whether given as a single injection or a 24-hour infusion. Although both agents were less cytotoxic for LCFU when administered in 24-hour infusions, host toxicity indicated that correspondingly larger doses of each agent could be given by infusion. The two agents also exhibited very similar cell-killing kinetics.