fludarabine + methotrexate + mercaptopurine

This is a combination chemotherapy regimen consisting of three antimetabolite agents—fludarabine, methotrexate, and mercaptopurine. Each drug interferes with DNA synthesis and cell replication through distinct but complementary mechanisms: - **Fludarabine** is a purine analog that inhibits DNA polymerase alpha, ribonucleotide reductase, and DNA primase, leading to inhibition of DNA synthesis and apoptosis in rapidly dividing cells. - **Methotrexate** is an antifolate agent that inhibits dihydrofolate reductase (DHFR), blocking the synthesis of tetrahydrofolate required for thymidylate and purine nucleotide production. - **Mercaptopurine** is a purine analog that disrupts nucleic acid biosynthesis by incorporating into DNA/RNA or inhibiting enzymes involved in purine metabolism. This combination has been used primarily in the treatment of acute lymphoblastic leukemia (ALL) as part of postremission intensification or maintenance therapy protocols. The regimen aims to maximize antileukemic efficacy by targeting multiple pathways critical for leukemic cell survival[1][3][7].