Simplified diagram of ifosfamide metabolism. Ifosfamide is a prodrug which is converted by P450 enzymes into the inactive decholoroethyl-ifosfamide and 4-hydroxy-ifosfamide, which exists in equilibrium with its tautomeric form aldoifosfamide. This spontaneously decomposes into active isophosphoramide mustard. The proportion of dechloroethylation required to produce chloroacetaldehyde is higher in ifosfamide (45%) than in cyclophosphamide (10%). Adapted from Zhang et al.  and Tascilar et al. .