## Cytarabine in AML Induction **Key Point:** Cytarabine (ara-C) is a cytidine analogue and the cornerstone antimetabolite in the standard 7+3 induction regimen for AML, combined with an anthracycline (daunorubicin or idarubicin). ### Mechanism of Action Cytarabine is converted to ara-CTP, which: - Inhibits DNA polymerase and ribonucleotide reductase - Causes chain termination during DNA synthesis - Is most effective in S-phase (rapidly dividing cells) ### Role in AML Treatment 1. **Induction phase:** 7 days of cytarabine (standard or high-dose) + 3 days of anthracycline 2. **Consolidation:** High-dose cytarabine (HiDAC) in younger, fit patients 3. **Maintenance:** Lower-dose regimens in selected cases **High-Yield:** The 7+3 regimen remains the gold standard induction therapy for fit patients with newly diagnosed AML, with complete remission rates of 60–80% in younger patients. **Clinical Pearl:** High-dose cytarabine (≥3 g/m² per dose) carries risk of neurotoxicity, particularly in patients >50 years or with renal impairment; dose reduction or alternative regimens (e.g., venetoclax + hypomethylating agents) are preferred in elderly/unfit patients. ### Comparison with Other Antimetabolites | Drug | Primary Use | Why Not for AML | | --- | --- | --- | | **Cytarabine** | AML, lymphoma | — | | **Gemcitabine** | Solid tumours (lung, pancreas, breast) | Not standard for AML; different spectrum | | **Methotrexate** | ALL, osteosarcoma, autoimmune | Different mechanism; not primary AML agent | | **5-FU** | Colorectal, gastric, breast cancer | Solid tumour agent; not used in AML | [cite:KD Tripathi 8e Ch 62]
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