Topotecan hydrochloride is primarily used in the treatment of certain types of cancer, particularly ovarian cancer, small cell lung cancer, and cervical cancer. It works by inhibiting the enzyme topoisomerase I, which is essential for DNA replication in cancer cells, thereby preventing their growth and proliferation.

In clinical settings, it is often administered intravenously and is commonly used when other treatments have not been effective. It is also utilized in combination with other chemotherapy drugs to enhance its efficacy. Additionally, topotecan hydrochloride is sometimes prescribed for pediatric patients with specific types of recurrent or refractory solid tumors.

The drug is known for its ability to cross the blood-brain barrier, making it a viable option for treating cancers that have metastasized to the central nervous system. However, its use is carefully monitored due to potential side effects, including bone marrow suppression, which can lead to anemia, neutropenia, and thrombocytopenia.