## **Core Concept**
The question pertains to the management of central nervous system (CNS) relapse in acute myeloid leukemia (AML), focusing on the chemotherapeutic agents used for intrathecal administration. CNS relapse in AML necessitates direct administration of chemotherapy into the cerebrospinal fluid (CSF) to effectively treat the leukemic cells within the CNS.

## **Why the Correct Answer is Right**
Intrathecal chemotherapy is crucial for treating CNS involvement in AML. Among the provided options, **Methotrexate** is a well-established agent for intrathecal administration in the context of CNS leukemia. It acts by inhibiting dihydrofolate reductase, an enzyme critical for DNA synthesis and cell replication, thereby selectively targeting rapidly dividing leukemic cells within the CNS.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is blank and cannot be evaluated.
- **Option B:** This option is also blank and cannot be assessed.
- **Option C:** Similarly, this option is blank and lacks information for critique.
- **Option D:** This option as well is blank, making it impossible to provide a reason for its incorrectness.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that **Methotrexate** is commonly used for intrathecal chemotherapy in cases of CNS leukemia, including AML. Another important aspect is the use of **Cytarabine** (Ara-C) and **Hydrocortisone** in combination with Methotrexate for intrathecal administration, enhancing the therapeutic efficacy and reducing side effects. However, the question specifically mentions Methotrexate.

## **Correct Answer:** . Methotrexate