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Methanol poisoning 

– mechanisms of toxicity

Methanol is not toxic itself, but it is metabolized to become highly toxic formic acid and its anion formate. Formic acid can create a metabolic acidosis, and both formic acid and formate inhibit the respiration chain in the mitochondria of the cells in the human body.

This results in a more severe acidosis and multiple organ failure, usually affecting the brain and the vision first.  Treatment is focused on blocking the enzyme alcohol dehydrogenase (ADH) with either ethanol or fomepizole, buffering the metabolic acidosis with bicarbonate, and using dialysis to remove methanol and formate, as well as to correct the metabolic acidosis. Folinic (or folic) acid may also be given to enhance the endogenous metabolism of formate. 

There are ways of treating methanol poisoning, including simplified treatment when blood gas is available, or other methods when blood gas in not available. 

If initiated early, treatment of methanol is highly effective, but it is often hampered by late diagnosis and lack of diagnostics and therapeutics. However, in lack of other options, the diagnostic process can be simplified – with or without the use of an arterial blood gas – and the treatment should follow a “use what you have”-principle.

Methanol is a widely available chemical used for many purposes: as a solvent in inks and dyes, in chemical synthesis and as a transportation fuel. Outbreaks of methanol poisoning often occur when methanol is added to alcoholic drinks. People do this to make money.

You can buy methanol in thousands of litres for industrial purposes. The methanol is then added to normal drinking alcohol (ethanol), diluting it and allowing it be sold on a larger profit. Methanol is not toxic itself, but it is metabolised to a very toxic substance: formic acid and/or formate. In the absence of ethanol, it takes about 12-24 hours to produce enough formate for symptoms of poisoning to appear. 

The main spike of victims typically appear over a few days with a “tail” of patients who can keep being poisoned for weeks or even months. Many are in a severe condition, in need of intensive care and dialysis.

As patients with methanol poisoning often need intensive medical care, outbreaks can rapidly overwhelm medical facilities, and ministry of health (MoH) staff generally do not have the capacity and knowledge to diagnose and treat them properly.

Outbreaks frequently occur all over the world with hundreds, possibly thousands, dying every year from methanol poisoning.

In 2016, more than 50 incidents globally were registered by the team. This was done through media monitoring alone - the only tool currently available for tracking outbreaks.

Clinical handling of methanol poisoning

A buffer (usually bicarbonate) is used to treat the acidic blood and other body tissues. This reduces the acid levels in the body and also reduces toxicity of formic acid/formate (the product of metabolised methanol), thus hopefully temporarily reversing the symptoms.

However, this will usually only postpone symptoms and the problem will most often not be solved until the metabolism of methanol is blocked.

Ethanol (regular alcohol) is the most commonly used antidote to block the metabolising of methanol. If the proper equipment is available, dialysis can also be used to eliminate the methanol and formate, as well as correct the often very severe metabolic acidosis.

Prevention posters for download

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Operations Support Unit, MSF-Hong Kong

Fiona Chuah, Medical Research & Analysis Officer

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