Methanol is rapidly absorbed by the stomach and intestines into the blood. It is also absorbed through the lungs and skin.
Mode of Action
Methanol causes less inebriation than ethanol, indeed, inebriation is not a prominent symptom of methanol toxicity unless a very large amount is consumed or ethanol is also ingested.
An asymptomatic latent period of 8–35 hours may precede the onset of symptoms of toxicity. If ethanol is consumed simultaneously in a sufficient amount, signs and symptoms of methanol poisoning may be considerably delayed or on occasions even averted. In such cases, ethanol intoxication is prominent and ingestion of methanol may not be suspected.
The rate of oxidation of methanol is only 1/7th to 1/10th of that of ethanol and thus its excretion requires several days and it tends to accumulate in the body.
The metabolism of Methanol in the body takes place as follows
Methanol
ß (Alcohol Dehydrogenase) – rate limiting step Formaldehyde
ß (Aldehyde Dehydrogenase)
Formic Acid
Lactic Acid
ß (Folate Dependent Mechanism)
CO2
H2O
Formaldehyde
Highly reactive. It is 33 times more toxic than methanol. But half life of formaldehyde elimination is only 1–2 minutes, thus no accumulation is detectable.
Formic Acid
It is six times more toxic than methanol. It is the major toxin and the cause of methanol toxicity. Methanol metabolism, in addition to Formic Acid, produces a large amount of Lactic Acid and other organic acids. Thus, it produces a severe degree of metabolic acidosis and widespread degenerative changes in the internal organs and the retina. Clinically, mortality rates and severity of visual disturbances correlate with the degree of acidosis.
