The toxicity of Methyl alcohol

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Methyl alcohol has a high toxicity in humans. If ingested, for example, as little as 10 mL of pure Methyl alcohol can cause permanent blindness by destruction of the optic nerve, and 30 ml is potentially fatal, although a fatal dose is typically 100–125 mL (4 fl oz) (i.e. 1–2 ml/kg of pure Methyl alcohol). Toxic effects take hours to start, and effective antidotes can often prevent permanent damage. Because of its similarities to ethanol (the alcohol in beverages), it is difficult to differentiate between the two (such is the case with denatured alcohol).
Methyl alcohol is toxic by two mechanisms. First, Methyl alcohol (whether it enters the body by ingestion, inhalation, or absorption through the skin) can be fatal due to its CNS depressant properties in the same manner as ethanol poisoning. Second, in a process of toxication, it is metabolized to formic acid (which is present as the formate ion) via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver. Methyl alcohol is converted to formaldehyde via alcohol dehydrogenase (ADH) and formaldehyde is converted to formic acid (formate) via aldehyde dehydrogenase (ALDH). The conversion to formate via ALDH proceeds completely, with no detectable formaldehyde remaining. Formate is toxic because it inhibits mitochondrial cytochrome c oxidase, causing the symptoms of hypoxia at the cellular level, and also causing metabolic acidosis, among a variety of other metabolic disturbances. Fetal tissue will not tolerate Methyl alcohol.
Ethanol is sometimes denatured (adulterated), and thus made undrinkable, by the addition of Methyl alcohol. The result is known as methylated spirit, "meths" (UK use) or "metho" (Australian slang). The latter should not be confused with "meth", a common U.S. abbreviation for methamphetamine.
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