Methanol Toxicity With a Deceptively Reassuring Ethanol Level
A 46-year-old man presents 18 hours after drinking homemade spirits at a party. He has nausea, blurred vision, and confusion. pH 7.18, bicarbonate 8 mmol/L, anion gap 30, measured osmolality 342 mOsm/kg, calculated osmolality 300 mOsm/kg, ethanol 80 mg/dL, creatinine 1.6 mg/dL. Funduscopy shows hyperemic optic discs. He smells of alcohol and has deep, sighing respirations. He is awake but cannot answer questions reliably. Serum methanol testing is send-out and will not return for 12 hours. The nearest dialysis center is 90 minutes away.
1. Calculate and interpret the osmolal and anion gaps, and decide whether to give fomepizole now. Justify your answer.
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Osmolal gap = 342 - 300 = 42 mOsm/kg; anion gap = 30. The combination of a high anion-gap metabolic acidosis, an elevated osmolal gap, visual symptoms, and optic-disc hyperemia is methanol until proven otherwise. The osmolal gap may fall as methanol is metabolized, so a normal gap later does not exclude toxicity. Give fomepizole now - 15 mg/kg loading dose - without waiting for the send-out methanol level. The ethanol level does not rule out significant methanol exposure; it may be a co-ingestant and is not reliably protective. Also give folinic acid and prepare for dialysis.
2. Which findings would prompt hemodialysis, and how would you adjust antidote dosing around dialysis?
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Dialysis for pH below 7.3, visual changes, methanol above 50 mg/dL, refractory acidosis, renal failure, or deteriorating mental status. Fomepizole around dialysis: give the next dose after dialysis and dose every 4 hours during intermittent hemodialysis because it is removed; if continuous renal replacement is used, dosing differs. Monitor methanol and formate if available, pH, bicarbonate, anion gap, and osmolality. Continue fomepizole until methanol is undetectable and acidosis has resolved.
3. How does the detectable ethanol level change your interpretation and monitoring plan?
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Ethanol 80 mg/dL may reflect recent drinking rather than protection; ethanol is also a substrate for alcohol dehydrogenase and can slow methanol metabolism, but a single level does not guarantee a sustained competitive block. If fomepizole is available, use it rather than ethanol. Monitor ethanol if it was given therapeutically and avoid hypoglycemia and over-sedation. The key monitoring is clinical: vision, mental status, pH, anion gap, and renal function. Do not discharge on the basis of a detectable ethanol level or a single gap.