A 28-year-old woman is admitted to a tertiary care hospital in Mumbai 4 hours after ingesting approximately 150 mL of ethylene glycol (antifreeze) in a suspected suicide attempt. She is alert, oriented, and reports mild nausea. Serum osmolality is 320 mOsm/kg (normal 280–300), and arterial pH is 7.32 with HCO₃⁻ 14 mEq/L. Urinalysis shows calcium oxalate crystals. What is the most appropriate immediate management?

Explanation

## Clinical Scenario Analysis This patient presents with early-stage ethylene glycol poisoning: - **Timeline:** 4 hours post-ingestion (within the window for ADH inhibition) - **Metabolic acidosis:** pH 7.32, low HCO₃⁻ (indicates formic acid accumulation) - **Elevated osmolality:** 320 mOsm/kg (osmolar gap present) - **Pathognomonic finding:** Calcium oxalate crystals in urine (ethylene glycol metabolite) ## Ethylene Glycol Metabolism & Toxicity ```mermaid flowchart TD A[Ethylene glycol ingestion]:::outcome --> B[Alcohol dehydrogenase metabolism]:::action B --> C[Glycolaldehyde]:::outcome C --> D[Glycolic acid]:::outcome D --> E[Glyoxylic acid]:::outcome E --> F[Oxalic acid]:::outcome F --> G[Calcium oxalate crystals]:::outcome G --> H[Acute kidney injury]:::urgent D --> I[Metabolic acidosis]:::urgent E --> J[Oxalate nephropathy]:::urgent ``` **Key Point:** Ethylene glycol itself is relatively non-toxic; the toxic metabolites (glycolic acid, glyoxylic acid, oxalic acid) cause: - Severe metabolic acidosis - Acute kidney injury (oxalate crystal deposition in renal tubules) - CNS depression - Pulmonary edema - Cardiac arrhythmias ## Why Fomepizole Is Superior to Ethanol | Feature | Fomepizole | Ethanol | |---|---|---| | **Specificity for ADH** | 1000× higher affinity than ethylene glycol | Competitive inhibitor; less specific | | **Dosing** | Fixed protocol (15 mg/kg load, then 10 mg/kg Q12H) | Requires frequent monitoring to maintain 100–150 mg/dL | | **Side effects** | Minimal; well-tolerated | CNS depression, hypoglycemia, lactic acidosis | | **Availability** | Widely available in India; preferred first-line | Older agent; now second-line | | **Monitoring** | Less frequent lab checks needed | Requires serial blood ethanol levels | **High-Yield:** Fomepizole is now the **preferred ADH inhibitor** for both methanol and ethylene glycol poisoning in most guidelines. It is more selective, safer, and easier to manage than ethanol. ## Management Protocol for Ethylene Glycol Poisoning 1. **Immediate:** Fomepizole 15 mg/kg IV loading dose 2. **Maintenance:** 10 mg/kg IV every 12 hours (or every 4 hours if on hemodialysis) 3. **Concurrent:** Correct metabolic acidosis with sodium bicarbonate 4. **Arrange:** Hemodialysis for symptomatic cases, severe acidosis, or renal dysfunction 5. **Supportive:** IV fluids, monitor urine output, check serum creatinine and osmolality **Clinical Pearl:** Calcium oxalate crystals in urine are a diagnostic clue for ethylene glycol poisoning. Early recognition and ADH inhibition within 12 hours of ingestion can prevent acute kidney injury. **Warning:** Do NOT delay fomepizole while awaiting serum ethylene glycol levels. The drug must be given within the first 12 hours to be effective. Once metabolites accumulate, hemodialysis becomes essential.