A analog of antimetabolite cytarabine (ara-C), with potential antineoplastic activity. Upon administration, thiarabine (T-araC) is phosphorylated to the triphosphate form T-araCTP and competes with cytidine for incorporation into DNA. This results in an inhibition of DNA replication and RNA synthesis, chain termination and may eventually decrease tumor cell proliferation. Compared to ara-C, T-araC appears to have a longer half-life and has a higher efficacy.