Busulfan belongs to which class of chemotherapeutic agents?

• A. Methotrexate
• B. Busulfan
• C. Bleomycin
• D. Doxorubicin

Answer: (B)

Chemotherapy drugs are grouped by how they affect DNA and its replication. Busulfan is an alkylating agent, specifically a bifunctional alkylating agent that adds alkyl groups to DNA and forms cross-links between strands. These cross-links hinder DNA strand separation during replication and transcription, leading to cell death, especially in rapidly dividing cells. This mechanism distinguishes busulfan from the other drugs: methotrexate is an antimetabolite that inhibits dihydrofolate reductase and blocks nucleotide synthesis; bleomycin is an antitumor antibiotic that causes DNA strand breaks via free radical formation; doxorubicin is an anthracycline that intercalates DNA and also generates free radicals. So busulfan fits the alkylating agent class.