Which of the following alkylating agents is a nitrogen mustard derivative that requires hepatic activation to form its active metabolite?

Explanation

## Cyclophosphamide: Mechanism and Activation **Key Point:** Cyclophosphamide is a prodrug that requires hepatic metabolism via the cytochrome P450 system (primarily CYP2C9 and CYP3A4) to generate its active alkylating metabolites, including phosphoramide mustard and acrolein. ### Nitrogen Mustard Structure Cyclophosphamide is a nitrogen mustard derivative — a class of alkylating agents containing a bis(2-chloroethyl)amino group. This structural feature allows it to form interstrand and intrastrand DNA crosslinks after activation. ### Activation Pathway 1. Hepatic oxidation produces phosphoramide mustard (active alkylating species) 2. Acrolein is also generated (responsible for hemorrhagic cystitis) 3. Inactive metabolites are excreted renally **Clinical Pearl:** The requirement for hepatic activation explains why cyclophosphamide has a broad spectrum of activity and why patients with severe hepatic dysfunction may have altered drug metabolism. **High-Yield:** Cyclophosphamide is unique among alkylating agents in requiring hepatic activation — most other alkylating agents (melphalan, chlorambucil, busulfan) are either directly active or undergo minimal metabolism. ### Comparison with Other Alkylating Agents | Agent | Activation | Route | Clinical Use | |-------|-----------|-------|---------------| | Cyclophosphamide | Hepatic (prodrug) | IV/PO | Lymphomas, solid tumors, autoimmune | | Melphalan | Direct (active) | IV/PO | Multiple myeloma | | Chlorambucil | Direct (active) | PO | CLL, lymphomas | | Busulfan | Direct (active) | IV/PO | CML, conditioning | **Mnemonic:** **CYCLO** = **C**ytochrome **P450** activation (Cyclophosphamide requires hepatic metabolism, unlike other alkylating agents)