Methanol is widely used as a solvent and as antifreeze. It is a potent poison with as little as 10 cm3 causing blindness and 30 cm3 can cause death. Toxicity can come from ingestion, inhalation and skin exposure. Mass poisonings have occurred from drinking alcoholic beverages made with contaminated ethanol and from accidental exposure. The major cause of methanol toxicity is its initial oxidation to formaldehyde, which is then converted to formate. The first step in the pathway is catalyzed by alcohol dehydrogenase and the production of formate is the result of several enzyme activities.
While both formaldehyde and formate are toxic, formaldehyde has a short metabolic half-life, whereas formate accumulates since its metabolism to CO2 is slow in humans. This leads to metabolic acidosis. The symptoms of methanol poisoning are an initial mild inebriation and drowsiness. Visual disturbances, such as blurred vision, diminished visual acuity, dilated pupils occur after about 6 h. Within 8–36 h nausea, vomiting, abdominal pain, headaches and possibly coma occur. Treatment for methanol poisoning is, first, to administer ethanol. This blocks metabolism since alcohol dehydrogenase has a greater affinity for ethanol than methanol. Second, sodium hydrogen carbonate is given intravenously to correct the metabolic acidosis.