Which drug is not classified as an antimetabolite?

Doxorubicin is not classified as an antimetabolite because it belongs to a different class of chemotherapy agents known as anthracyclines. Antimetabolites primarily interfere with DNA and RNA synthesis by mimicking the natural substrates of these processes. Common examples of antimetabolites include Methotrexate, which inhibits folate metabolism, Cytarabine, which mimics the nucleoside cytidine, and Capecitabine, which is a prodrug that is converted to fluorouracil affecting pyrimidine metabolism.

On the other hand, Doxorubicin works by intercalating into DNA strands, disrupting the function of the DNA, and inhibiting topoisomerase II, an enzyme essential for DNA replication and transcription. This mechanism of action is distinct from that of antimetabolites, emphasizing why Doxorubicin is categorized separately from the others listed.