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I have a friend who last year suffered severe drug addiction and decided to consume windshield washer fluid that contains methanol/isopropanol. He drank it from Saturday to Wednseday before being caught in college and taken to A&E.

Luckily for him, he didn't die or suffer from retinal damage/organ damage/kidney damage. The doctors were baffled. He had 2900mg/L of methanol in his blood and was treated with fomepizole.

The nephrologist said that he was lucky that the mixture contained isopropanol (propan-2-ol) because that most likely inhibitied alcohol dehydrogenase in his liver from converting methanol to formaldehyde and then formic acid.

Methanol in it's unconverted form is not harmful to the body.

Is this true or not?

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  • Question and post content ask two different things.
    – Thomas
    Nov 18, 2020 at 21:07
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    Of some note: since 2018 methanol is banned in windshield washer fluid in the EU.
    – Fizz
    Nov 19, 2020 at 1:51

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The nephrologist is right, in toxicology we learn that the theory behind a methanol intoxication is due to the fact that methanol is metabolized by alcohol dehydrogenase to formaldehyde and then aldehyde dehydrogenase metabolizes formaldehyde into formic acid.

The trick however is that, since ethanol uses the same enzymes as methanol to be metabolized, and once those enzymes have more affinity to ethanol than for methanol, then methanol will not be metabolized and thus formic acid will never be formed (which is the main source of toxicity) in summary, ethanol as fomepizole act as a competitive inhibitor of alcohol dehydrogenase.

Your question regards isopropanol, which uses the same enzymes than ethanol and methanol and once isopropanol shows a higher affinity for AD (alcohol dehydrogenase) than methanol, and

Isopropanol does not get metabolized to a toxic acid metabolite like ethylene glycol and methanol

then same logic is applied, it can act as competitive inhibitor of alcohol dehydrogenase.

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    I find this explanation a bit dubious because isopropanol itself is poisonous, being converted to acetone by the same dehydrogenase... en.wikipedia.org/wiki/Isopropyl_alcohol#Toxicology However "the metabolites of isopropyl alcohol are considerably less toxic", so it would depend how much of the latter is ingested too... "fatal isopropyl alcohol ingestion usually have blood concentrations of hundreds of mg/dL"
    – Fizz
    Nov 19, 2020 at 1:44

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