Cytosine arabinoside interferes with the synthesis of DNA. It is an antimetabolic agent with the chemical name of 1β-arabinofuranosylcytosine. 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. Cytosine arabinoside also inhibits both DNA[9] and RNA polymerases and nucleotide reductase enzymes needed for DNA synthesis.
When used as an antiviral, cytarabine functions by inhibiting deoxycytidine use.[10]
Cytarabine is rapidly deaminated in the body into the inactive uracil derivative and therefore is often given by continuous intravenous infusion.