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Ethylene glycol is metabolized to glycolic and oxalic acids, producing a high-anion-gap metabolic acidosis and renal failure; the oxalic acid binds calcium, forming calcium oxalate crystals that appear in urine. Fomepizole (4-methylpyrazole) and adjunctive bicarbonate/calcium therapy are standard treatments for ethylene glycol poisoning, matching this patient’s management and laboratory findings [Scalley, 2002, PMID 12322772].