## Investigation of Choice for Cytarabine Neurotoxicity Risk ### Why Renal Function Assessment is Correct **Key Point:** Cytarabine-induced neurotoxicity (especially at high doses ≥3 g/m²) is strongly correlated with impaired renal clearance and elevated drug accumulation. Baseline assessment of creatinine clearance is the single most predictive investigation for neurotoxicity risk. **High-Yield:** Cytarabine is renally eliminated as unchanged drug and active metabolites. Patients with: - Creatinine clearance <60 mL/min - Age >50 years - Elevated baseline creatinine - Concurrent nephrotoxic drugs ...have significantly higher risk of CNS toxicity (confusion, ataxia, dysarthria, coma, seizures). **Clinical Pearl:** The dose of high-dose cytarabine should be reduced or avoided in patients with renal impairment. Standard dosing is safe; high-dose regimens (used in AML consolidation) carry 5–25% neurotoxicity risk if renal function is not optimized. ### Mechanism of Toxicity Cytarabine undergoes: 1. Rapid deamination by cytidine deaminase → uracil arabinoside (inactive) 2. Phosphorylation to ara-CTP (active form) 3. Renal excretion of unchanged drug and metabolites Renal impairment → ↑ ara-CTP accumulation → CNS penetration → neurotoxicity ### Investigation Hierarchy | Investigation | Utility | Timing | |---|---|---| | Serum creatinine & CrCl | **Predictive of toxicity risk** | **Before each cycle** | | CSF analysis | Diagnostic (if toxicity occurs) | Only if symptoms develop | | LC-MS metabolite levels | Research tool; not routine | Not standard practice | | Neuropsych testing | Baseline assessment only | Not predictive | [cite:KD Tripathi 8e Ch 65]
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