It is variable. About 60–240 ml is fatal. But, even 30–60 ml have proved fatal and recovery has occurred after absorption of 500–600 ml of absolute methanol.
The smallest amount reported to cause death is 15 ml of 40% methanol and 4 ml is the lowest recorded toxic dose.
Usually 24–36 hours. But, may be delayed for 3–4 days.
Signs and Symptoms of Methanol Consumption
Signs and symptoms vary according to
- Amount Ingested,
- Presence of Folate Difienciency
- Whether or not there was simultaneous ethanol consumption.
Onset of symptoms is prolonged – as long as 24-36 hours – when sufficient toxic metabolites have accumulated
- Severe abdominal pain or cramps in epigastric region due to pancreatic necrosis
- Muscular weakness
- Effect on CNS is more intense and persistent than ethanol
- Visual disturbances – they vary from photophobia, blurred vision, concentric diminution of visual field for color to be followed by partial blindness. But, these visual changes are not uniformly noted. Cloudy, blurred, misty or indistinct vision (described as similar to ‘stepping out in to a show field’) is typical.
Impairment of vision due to methyl alcohol intoxication is abrupt in onset. And if visual functions return, it generally does so in the first six days.
- Large, symmetrical and central scotomas
- Decreased pupillary response to light.
This has prognostic significance. No patient with normally reactive pupils has suffered permanent visual loss. However, the decreased pupillary reaction may occur in patients who have had a complete recovery.
The mechanism of selective involvement of the optic nerve in methanol toxicity remains unknown.
Other drugs with proven but less devastating toxic effects on the optic nerve include
- Sulfonamides Digitalis
- Heavy metals
These above features are accompanied by
- Subnormal temperature
Despite severe acidosis, “Kussmaul Respiration” (i.e. intense hyperventilation or air hunger) is not common because of respiratory depression caused by intoxication. In moribund patients, the respiration is slow, shallow, gasping and “fish–mouth”.
Coma follows unconsciousness and death occurs from cardiorespiratory failure and is almost always preceded by blindness.
- Delirium and coma may last for 2–3 days.
- Coma induced by methanol is longer in its onset and also lasts longer than in thanol.
- Although recovery is common from drunkenness from ethanol, it is nearly always fatal in case of methanol poisoning.