drugs, it acts by disrupting the DNA replication process of dividing cancer cells in the body. Hydroxyurea selectively inhibits ribonucleoside diphosphate reductase, an enzyme required to convert ribonucleoside diphosphates into deoxyribonucleoside diphosphates, thereby preventing cells from leaving the G1/S phase of the cell cycle. This agent also exhibits radiosensitizing activity by maintaining cells in the radiation-sensitive G1 phase and interfering with DNA repair. Biochemical research has explored its role as a DNA replication inhibitor which causes deoxyribonucleotide depletion and results in DNA double strand breaks near replication forks (see DNA repair). Repair of DNA damaged by chemicals or irradiation is also inhibited by hydroxyurea, offering potential synergy between hydroxyurea and radiation or alkylating agents. Hydroxyurea has many pharmacological applications under the Medical Subject Headings classification system: Antineoplastic Agents – Substances that inhibit or prevent the proliferation of neoplasms. Antisickling Agents – Agents used to prevent or reverse the pathological events leading to sickling of erythrocytes in sickle cell conditions. Nucleic Acid Synthesis Inhibitors – Compounds that inhibit cell production of DNA or RNA. Enzyme Inhibitors – Compounds or agents that combine with an enzyme in such a manner as to prevent the normal substrate-enzyme combination and the catalytic reaction. Cytochrome P-450 CYP2D6 Inhibitors – Acts as an inhibitor to one of the most important enzymes involved in the metabolism of xenobiotics in the body, CYP2D6 a member of the cytochrome P450 mixed oxidase system. Society and culture Brand names Brand names include: Hydrea, Litalir, Droxia, and Siklos. References External links Antineoplastic antimetabolites Bristol Myers Squibb IARC Group 3 carcinogens Wikipedia medicine articles ready to translate Sickle-cell disease Ureas World Health Organization essential medicines X