Alkylating agents are compounds that work by adding an alkyl group to the guanine base of the DNA molecule, preventing the strands of the double helix from linking as they should. This causes breakage of the DNA strands, affecting the ability of the cancer cell to multiply. Eventually, the cancer cell dies. Alkylating agents were one of the first classes of drugs to be used against cancer.

There are five traditional categories of alkylating agents:

• Nitrogen mustards (eg, bendamustine, chlorambucil, cyclophosphamide, ifosfamide, mechlorethamine, melphalan)
• Nitrosoureas (eg, carmustine, lomustine, streptozocin)
• Alkyl sulfonates (eg, busulfan)
• Triazines (eg, dacarbazine, temozolomide)
• Ethylenimines (eg, altretamine, thiotepa)