Methyl alcohol Poisoning

Nature

  • Methyl alcohol also known as methanol.
  • It is colourless liquid.
  • Its boiling point is 64.7 degree Celsius.
  • It is miscible with water and alcohol in all proportion.

Use

  • Methyl alcohol is used as a solvent.
  • It is used in the manufacture of dyes and varnishes.
  • It is also used for the preparation of denatured spirit commonly known as methylated spirit.

Administration

It is consumed in the form of diluted methylated spirit which is sold to the public by clandestine vendors as alcoholic beverages.

Fatal dose

  • Fatal dose for methyl alcohol is usually 60-200ml.
  • Yet 15ml has caused blindness.

Fatal period

  • Usually 24 to 36 hours.

Absorption and metabolism

Methanol is rapidly absorbed from the gastrointestinal tract, through lungs and skin.

It is metabolized in liver. It is first metabolized to formaldehyde by the enzyme alcohol dehydrogenase and then the formaldehyde is further metabolized into formic acid by the enzyme aldehyde dehydrogenase. Methanol follows zero order kinetics and the half-life is about 20 to 60 hours.

Mode of action

Methanol itself is not toxic but two metabolites formed formaldehyde and formic acid is highly toxic. These compounds are responsible for causing profound metabolic acidosis and visual defect and blindness.

Sign and symptoms

  • Nausea
  • Vomiting
  • Abdominal pain
  • Headache
  • Breathlessness
  • Dizziness
  • Vertigo
  • Tachycardia
  • Hypotension
  • Profound metabolic acidosis
  • Convulsions
  • Delirium
  • Coma
  • Visual disturbances
  • Blurring of vision, or frank blindness.
  • Retrobulbar degeneration in the form of necrosis.
  • Photophobia
  • Constriction of visual fields
  • Hyperemia of optic disk
  • Papilledema
  • Decrease pupillary light reflex
  • Retinal edema

Treatment

  • Protect eyes from light.
  • Maintain respiration, circulation and blood pressure.
  • Gastric lavage with sodium bicarbonate
  • Antidote ‚ÄĒ ethanol is the specific antidote.

Postmortem findings

  • Cyanosis
  • Stomach and intestine may be hyperemic and inflamed.
  • Patchy submucosal hemorrhages may be seen.
  • Pulmonary edema
  • Cerebral edema
  • Retinal edema
  • Necrosis of myelinated portion of optic nerve.

Forensic examination and test for detection

  • Chromotropic acid test- On performing this test, a violet colour appears which indicates the presence of methyl alcohol.
  • Schiffs reagent test- On performing this test, a pink to purple colour is developed which indicates the presence of methyl alcohol.
  • Gas chromatography
  • Spectrophotometer
  • Colorimeter

Medico legal aspects

Most of deaths are due accidental consumption of methanol due to non-available of regular alcohol or due to adulteration of regular alcohol with methanol.

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