Clinical Pharmacology of Cyclophosphamide and Ifosfamide

The oxazaphosphorine cyclophosphamide (CPA) and ifosfamide (IFO) are two commonly used DNAalkylating agents in cancer chemotherapy. This review highlights the pharmacokinetics and pharmacodynamics of the two important agents. As alkylating agents, CPA and IFO are usually combined with other anticancer drugs in the chemotherapy of solid tumors and hematological malignancies to obtain synergistic or additive anticancer effect due to complementary mechanism of action. Both compounds are prodrugs that are activated via 4-hydroxylation by cytochrome P450s such as CYP2B6 and CYP3A4 to generate alkylating nitrogen mustards (phosphoramide mustard and ifosforamide mustard) and the byproduct acrolein. The resultant mustards can alkylate DNA to form DNA-DNA cross-links, leading to inhibition of DNA synthesis and cell apoptosis. Both CPA and IFO are also inactivated by N-dechloroethylation, resulting in N-dechloroethylated metabolites and the byproduct chloroacetaldehyde. Acrolein is the causative agent for hemorrhagic cystitis, whereas chloroacetaldehyde induces nephrotoxicity and neurotoxicity. Pharmacokinetics of CPA and IFO is markedly influenced by route of administration and duration of treatment, age, comedication, liver and renal function. Large interpatient variability in pharmacokinetics, clinical response rate and toxicity has been observed in cancer patients treated with CPA or IFO. Resistance to CPA or IFO occurs due to decreased activation by CYP3A4 and CYP2B6, increased deactivation of the agents, decreased entry into or increased efflux from tumor cells, increased cellular thiol level, increased DNA repair capacity, and/or deficient apoptotic response to DNA damage. A full understanding of factors affecting the pharmacokinetics, pharmacodynamics, toxicology and pharmacogenetics of CPA and IFO is important to optimize the dose and regimens of CPA and IFO in cancer chemotherapy.