Cytosine arabinoside, also known as cytarabine or Ara-C, is a chemotherapy medication used to treat specific cancers. It interferes with the growth of cancer cells, disrupting the rapid proliferation characteristic of hematological malignancies.
Medical Uses of Cytosine Arabinoside
Cytosine arabinoside is widely used to treat acute myeloid leukemia (AML), a fast-growing cancer of the blood and bone marrow. It is a primary component of induction and consolidation chemotherapy regimens for newly diagnosed AML patients. The drug is also a standard treatment for acute lymphocytic leukemia (ALL), particularly in children and adults, targeting the abnormal white blood cells that multiply quickly.
Beyond acute leukemias, cytosine arabinoside finds application in other blood cancers. It is used in the blast crisis phase of chronic myeloid leukemia (CML). Certain types of non-Hodgkin’s lymphoma, especially those affecting the central nervous system, may also be treated with this medication.
Mechanism of Action
Cytosine arabinoside is an antimetabolite, mimicking natural substances involved in cell metabolism. It is converted into an active form called cytosine arabinoside triphosphate. This active form acts like a faulty building block.
When cancer cells attempt to replicate their DNA, they mistakenly incorporate this faulty building block into their genetic material. Its altered structure prevents the DNA chain from extending further. This disruption primarily affects cells during the S-phase of the cell cycle, when DNA synthesis occurs. The damaged DNA ultimately triggers programmed cell death (apoptosis), reducing the cancer cell population.
Administration and Dosing
Cytosine arabinoside can be administered through several routes depending on the specific cancer and treatment protocol. The most common method is intravenous (IV) infusion, where the drug is delivered directly into a vein. This can be given continuously over several days or as a shorter infusion.
Another method involves subcutaneous injection, where the drug is injected under the skin. For cancers affecting or threatening the central nervous system, such as meningeal leukemia, cytosine arabinoside can be given as an intrathecal injection directly into the cerebrospinal fluid. Dosing regimens vary considerably, often involving treatment cycles over specific durations. The dosage and schedule are determined by the treating physician, taking into account the type of cancer, the patient’s overall health, and whether a standard-dose or high-dose cytarabine (HDAC) regimen is required.
Common Side Effects
Treatment with cytosine arabinoside can lead to several side effects. Bone marrow suppression, also known as myelosuppression, is one of the most significant and common. This condition results in a decrease in the production of blood cells in the bone marrow. Low white blood cell counts increase the risk of infections, while reduced red blood cells can cause fatigue and weakness. A drop in platelet counts may lead to easy bruising or bleeding.
Gastrointestinal effects are also frequently observed during treatment. These can include nausea, vomiting, and diarrhea. Many patients also experience mucositis, which manifests as painful sores or inflammation in the mouth and along the digestive tract. These symptoms can impact a patient’s ability to eat and maintain nutrition.
“Cytarabine syndrome” may develop in some individuals, typically within 6 to 12 hours after drug administration. This syndrome is characterized by fever, muscle aches, bone pain, a skin rash, and sometimes conjunctivitis.
High doses of cytosine arabinoside carry a risk of neurological side effects. Patients may experience issues such as cerebral and cerebellar dysfunction, which can affect coordination and balance. Other potential neurological effects include peripheral neuropathy, presenting as numbness or tingling in the extremities, and more severe issues like personality changes, seizures, or coma. Medical teams closely monitor patients for these and other side effects, implementing strategies to manage symptoms and provide supportive care throughout the treatment course.