A 52-year-old man with newly diagnosed acute myeloid leukemia (AML) presents to the oncology clinic. He has been started on cytarabine (Ara-C) as part of induction chemotherapy. On day 5 of treatment, he develops severe mucositis, diarrhea, and a white blood cell count of 0.8 × 10⁹/L. He is afebrile with stable vital signs. What is the most appropriate immediate next step in management?

Explanation

## Management of Antimetabolite-Induced Myelosuppression ### Clinical Context Cytarabine (Ara-C) is a pyrimidine antimetabolite that causes dose-dependent myelosuppression. The patient's WBC of 0.8 × 10⁹/L with severe mucositis indicates significant bone marrow toxicity requiring immediate intervention. ### Correct Management Approach **Key Point:** When severe myelosuppression develops during antimetabolite therapy, the standard approach is to: 1. **Hold the offending agent** to allow bone marrow recovery 2. **Initiate G-CSF (granulocyte colony-stimulating factor)** to accelerate neutrophil recovery 3. **Provide supportive care** including antimicrobial prophylaxis, transfusions as needed, and mucosal care **High-Yield:** Continuing cytarabine at the same dose in the face of WBC <1.0 × 10⁹/L risks life-threatening infections and fatal bone marrow aplasia. G-CSF reduces the duration of neutropenia by 3–5 days and decreases infection risk. ### Why This Approach **Clinical Pearl:** Antimetabolites like cytarabine, 5-fluorouracil, and methotrexate are S-phase specific and cause cumulative, reversible myelosuppression. Once severe toxicity is recognized, holding the drug and supporting the marrow with growth factors is the standard of care [cite:Harrison 21e Ch 101]. **Mnemonic: HOLD-GF-SUPPORT** — **H**old the drug, **O**pen supportive measures, **L**et marrow recover, **D**ose adjustment later; **G**-CSF, **F**luids/transfusions; **S**upport with antibiotics, **U**rinalysis/monitoring, **P**rophylaxis, **P**ain control, **O**ral care, **R**ound-the-clock labs, **T**herapy reassessment. ### Table: Management of Antimetabolite Toxicity by Grade | Grade | WBC (×10⁹/L) | Action | | --- | --- | --- | | 1 | 3.0–3.9 | Continue, monitor | | 2 | 2.0–2.9 | Consider dose reduction or G-CSF | | 3 | 1.0–1.9 | Hold, initiate G-CSF | | 4 | <1.0 | Hold, G-CSF, intensive support | ### Why Not the Other Options Continuing at the same dose (Option 0) risks sepsis and aplasia. Switching agents (Option 2) abandons proven AML induction therapy without addressing the underlying toxicity. Dose reduction without growth factor support (Option 3) is suboptimal because it delays marrow recovery and may compromise treatment efficacy.