HYDROSAR Capsules HYDROSAR contains Hydroxyurea, an antimetabolite that selectively inhibits ribonucleotide reductase, the enzyme responsible for converting ribonucleotides to deoxyribonucleotides. This inhibition starves the cell of necessary DNA building blocks, selectively blocking DNA synthesis without interfering with RNA or protein synthesis, which leads to cell cycle arrest in the S-phase. It is indicated for the treatment of resistant chronic myelogenous leukemia (CML), locally advanced squamous cell carcinomas of the head and neck (excluding the lip) in combination with radiation therapy, and for reducing the frequency of painful crises and the need for blood transfusions in adult and pediatric patients with sickle cell anemia.