Methanol Poisoning with Severe Acidosis and Visual Symptoms
A 41-year-old man is brought to the ED 10 hours after drinking an unknown homemade spirit at a party. He complains of blurred vision and nausea. Vital signs: heart rate 108/min, blood pressure 102/64 mmHg, respiratory rate 26/min, temperature 36.8°C. He is alert but tachypneic. Laboratory: arterial pH 7.22, PaCO2 24 mmHg, bicarbonate 10 mmol/L, sodium 140, chloride 104, potassium 4.1, creatinine 1.0, glucose 96 mg/dL; measured serum methanol 42 mg/dL; ethanol less than 10 mg/dL; osmol gap 28 mOsm/kg. Fundoscopy shows hyperemic optic discs but no papilledema. Fomepizole 15 mg/kg IV was given 1 hour ago. The nephrologist is unsure whether to start hemodialysis because the methanol level is below 50 mg/dL, and the ICU asks how to dose fomepizole if dialysis is started.
1. Decide whether hemodialysis is indicated and justify with criteria beyond the methanol concentration.
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Hemodialysis is indicated despite a methanol level of 42 mg/dL because the decision is not based on the number alone. This patient has severe metabolic acidosis (pH 7.22, bicarbonate 10), an elevated osmol gap, and visual symptoms with hyperemic optic discs. Those features indicate that methanol has been metabolized to formate, which inhibits cytochrome oxidase and causes retinal and optic nerve toxicity. The traditional dialysis threshold of 50 mg/dL is a guide, not a rule; dialysis is also indicated for visual impairment, severe or refractory acidosis, renal failure, or deterioration despite supportive care. The measured level may also be falsely reassuring if the assay cross-reacts or if the ingestion is ongoing; the osmol gap of 28 supports a significant load. Fomepizole was given, which is correct, but it blocks further metabolism without removing existing methanol or formate. Dialysis removes methanol and, to a lesser extent, formate, and it corrects the acidosis. Waiting for the level to rise above 50 mg/dL risks irreversible visual loss. Start intermittent hemodialysis now and continue adjunctive therapy.
2. Explain fomepizole dosing during and after intermittent hemodialysis, and alternatives.
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Fomepizole is a competitive inhibitor of alcohol dehydrogenase. It is dialyzable, so the standard q12h dosing is inadequate during hemodialysis. Give the next dose every 4 hours while dialysis is running. If a dialysis session lasts longer than 6 hours, give the scheduled dose after dialysis ends; if it is shorter, resume the usual q12h schedule after dialysis, but do not let more than 4 hours pass during dialysis without a dose. Because the loading dose was already given, document the time and adjust. If fomepizole is unavailable, ethanol is the alternative: give an IV loading dose to achieve a serum ethanol concentration of about 100-150 mg/dL and maintain it, recognizing that ethanol is also dialyzable and requires redosing during dialysis. Ethanol infusion is harder to titrate, causes hypoglycemia and intoxication, and requires frequent levels. Do not use fomepizole as a reason to delay dialysis. In a patient with severe acidosis and visual signs, both antidote and extracorporeal removal are needed.
3. Discuss adjunctive treatments and endpoints for stopping dialysis.
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Give sodium bicarbonate to correct severe acidosis, targeting a pH above 7.3 rather than full normalization, while monitoring potassium and calcium. Folinic acid (leucovorin) 1 mg/kg IV every 4-6 hours is preferred over folic acid because it enters the folate pathway more readily and may enhance formate metabolism; continue for the duration of toxicity. Supportive care includes thiamine before glucose if hypoglycemia is a concern, airway protection if mental status deteriorates, and serial visual and neurologic examinations. Endpoints for stopping dialysis are a methanol concentration below about 20-25 mg/dL, resolution of metabolic acidosis, and stable or improving visual symptoms. Because methanol can redistribute, recheck the level 2-4 hours after dialysis and continue fomepizole until the methanol is below the treatment threshold and acidosis has resolved. If the level rebounds or acidosis persists, repeat dialysis. Involve ophthalmology early, but do not wait for their consultation to start treatment.