Cytarabine, Methotrexate, and Thiotepa Intrathecal Chemotherapy

This triple-drug combination of cytosine arabinoside (cytarabine), methotrexate, and thiotepa is a chemotherapy regimen used primarily for treating meningeal involvement by various malignancies. It is administered intrathecally (directly into the cerebrospinal fluid) via an Ommaya reservoir or lumbar puncture. **Components and Mechanisms:** * **Methotrexate**: An antimetabolite that inhibits dihydrofolate reductase. * **Cytosine arabinoside (Cytarabine)**: A pyrimidine nucleoside analog that inhibits DNA synthesis. * **Thiotepa**: An alkylating agent that cross-links DNA. **Clinical Applications:** Primary indications include leptomeningeal carcinomatosis from solid tumors (particularly breast and lung cancer), meningeal involvement by malignancies, and primary CNS lymphoma (often as part of the MATRix regimen with rituximab). **Efficacy and Outcomes:** While some research suggests the triple-drug combination may offer better response rates than single-agent methotrexate in certain populations, other studies have reported unacceptable myelosuppression without improving response rates or survival compared to single-agent methotrexate plus radiotherapy. The MATRix regimen, incorporating this combination with rituximab, has shown improved outcomes in primary CNS lymphoma patients. **Side Effects and Toxicity:** Common adverse effects include myelosuppression (reported in up to 77% of patients), neurological toxicity, and chemical meningitis. The risk of chemical meningitis can be reduced by adding hydrocortisone. Cerebellar toxicity, particularly with high-dose cytarabine, is also noted. Careful monitoring is essential, especially for patients with renal dysfunction due to increased risk of cytarabine-induced neurotoxicity.