Methanol poisoning

Methanol is metabolised by alcohol dehydrogenase to formic acid. A metabolic acidosis develops due to lactate production in addition to the accumulation of formate

• methanol is metabolized by the enzyme alcohol dehydrogenase (ADH) in the liver, via formaldehyde to formic acid, the latter being responsible for the adverse effects seen in methanol poisoning
• methanol toxicity evolves from a combination of the metabolic acidosis (H+ production) and an intrinsic toxicity from the formate anion itself

Methanol poisonings occur as isolated episodes caused by accidental or intentional ingestion, or epidemics (1).

Clinical manifestations of pure methanol toxicity initiate within 0.5–4 h after ingestion and include gastrointestinal disorders (nausea, vomiting, and abdominal pain) and central nervous system (CNS) suppression (confusion and drowsiness) (2)

• depending on the absorbed dose, after a latent period of 6–24 h, decompensated metabolic acidosis occurs with blurred vision, photophobia, diplopia, early or late blindness, and less commonly, nystagmus
• a suspicious sign of methanol poisoning is the occurrence of blurred vision with normal consciousness

Mortality and severity of clinical effects are well associated with the severity of CNS depression, hyperglycemia, and metabolic acidosis, but not with serum methanol concentration (1,2)

Treatment consists of buffer such as sodium bicarbonate to correct metabolic acidosis and antidote to inhibit metabolism of methanol to its toxic metabolite, formic acid (1,2)

• if necessary, haemodialysis is supplied to further correct the acidosis, and remove both methanol and formate

Reference:

1. Paasma R, Hovda KE, Jacobsen D. Methanol poisoning and long term sequelae - a six years follow-up after a large methanol outbreak. BMC Clin Pharmacol. 2009 Mar 27;9:5.
2. Nekoukar Z, Zakariaei Z, Taghizadeh F, Musavi F, Banimostafavi ES, Sharifpour A, Ebrahim Ghuchi N, Fakhar M, Tabaripour R, Safanavaei S. Methanol poisoning as a new world challenge: A review. Ann Med Surg (Lond). 2021 Jun 2;66:102445.