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NBME 23 Answers

nbme23/Block 2/Question#29

Which of the following pairs of drugs interferes ...

Lomustine and cyclophosphamide

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submitted by gabeb71(15),

Lomustine ia an alkylating nitrosourea compound used in chemotherapy. Alkylating agents crosslink DNA.

Cyclophosphamide metabolizes into a phosphoramide mustard. Phosphoramide mustard forms DNA crosslinks both between and within DNA strands

Cholchicine and Vinblastine work on microtubules

Methotrexate and 5-FU both work on purine metabolism.

Cytosine arabinoside interferes with the synthesis of DNA. Its mode of action is due to its rapid conversion into cytosine arabinoside triphosphate, which damages DNA when the cell cycle holds in the S phase (synthesis of DNA). Rapidly dividing cells, which require DNA replication for mitosis, are therefore most affected.

smc213  To clarify Methotrexate (inhibits dihydrofolate reductase) and 5-FU (inhibits thymidylate synthase) in the Pyrimidine synthesis pathway. 6-MP inhibits Glutamine PRPP amidotransferase in the PURINE synthesis pathway +