## Drug of Choice for AML Induction **Key Point:** Cytarabine (cytosine arabinoside) is the backbone of standard induction chemotherapy for acute myeloid leukaemia, typically combined with an anthracycline (e.g., daunorubicin) in the "7+3" regimen. ### Mechanism of Action Cytarabine is a deoxycytidine analogue that: 1. Inhibits ribonucleotide reductase, reducing deoxyribonucleotide pools 2. Is phosphorylated to cytarabine triphosphate (ara-CTP) 3. Incorporates into DNA and causes chain termination 4. Leads to apoptosis in rapidly dividing cells ### Why Cytarabine for AML? | Feature | Cytarabine | Methotrexate | Gemcitabine | Fluorouracil | |---------|-----------|--------------|------------|---------------| | **Mechanism** | DNA chain terminator | DHFR inhibitor | Ribonucleotide reductase inhibitor | Thymidylate synthase inhibitor | | **Cell cycle phase** | S-phase specific | S-phase specific | S-phase specific | S-phase specific | | **Standard use in AML** | **Yes (backbone)** | No | No | No | | **Dose intensity** | High-dose for AML | Moderate | Moderate | Moderate | | **Synergy with anthracyclines** | **Excellent** | Poor | Poor | Poor | **High-Yield:** The "7+3" regimen (cytarabine 100–200 mg/m² daily × 7 days + daunorubicin 60–90 mg/m² daily × 3 days) is the gold-standard induction therapy for newly diagnosed AML in fit patients [cite:Harrison 21e Ch 104]. **Clinical Pearl:** High-dose cytarabine (3 g/m² IV) is used in consolidation therapy and for CNS prophylaxis in AML. Cerebellar toxicity is a dose-limiting side effect at high doses. ### Cytarabine Toxicity Profile - **Myelosuppression:** severe, dose-limiting - **Mucositis:** common - **Cerebellar syndrome:** at high doses (>3 g/m²) - **Conjunctivitis:** can be prevented with prophylactic eye drops - **Hepatotoxicity:** rare but possible
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