Topotecan is a chemotherapy medication primarily used to treat certain types of cancer, including ovarian cancer and small cell lung cancer. It works by inhibiting the action of an enzyme called topoisomerase I, which is essential for DNA replication. By disrupting this process, topotecan helps to prevent cancer cells from dividing and growing. This drug is usually administered intravenously or orally and may be given in cycles to allow the body to recover between treatments. Common side effects include nausea, vomiting, and low blood cell counts, which can increase the risk of infections and bleeding.