Metabolism of high doses of cyclophosphamide.

The excretion of cyclophosphamide and the enzymatically derived metabolites 4-ketocyclophosphamide and carboxyphosphamide has been measured in four patients after the administration of cyclophosphamide (5 g). At this dose the enzymes responsible for the biotransformation and detoxification of cyclophosphamide are not saturated. In two patients the metabolite profile was unaffected by a previous high dose of cyclophosphamide and in one patient a small primary dose did not alter metabolism.