Irinotecan hydrochloride is primarily used in the treatment of colorectal cancer. It is often administered in combination with other chemotherapy drugs, such as 5-fluorouracil and leucovorin, to enhance its effectiveness. The drug works by inhibiting topoisomerase I, an enzyme crucial for DNA replication, thereby preventing cancer cells from dividing and growing. In addition to colorectal cancer, it is also utilized in the management of other malignancies, including small cell lung cancer and certain types of pancreatic cancer. Its application extends to second-line therapy for patients who have not responded adequately to initial treatments. The drug is typically administered intravenously, and its dosage is carefully calibrated based on the patient's body surface area and overall health condition. Due to its potent nature, patients undergoing treatment with Irinotecan hydrochloride are closely monitored for adverse effects, such as severe diarrhea and neutropenia, which require prompt management to ensure patient safety and treatment efficacy.