Monograph: |
Methanol.
(Methyl Alcohol)
A clear, colourless, flammable liquid with a characteristic
odour. Wt per mL about 0.79 g. B.p. about 65Β°. Miscible with
water, alcohol, ether, and most other organic solvents. Store
in airtight containers.
CAUTION. Suitable precautions should be taken to avoid skin
contact with methyl alcohol as it can penetrate skin and pro-
duce systemic toxicity.
Adverse Effects
Immediate signs of acute poisoning following ingestion of
methyl alcohol resemble those of alcohol intoxication , but are
milder. Characteristic symptoms of methyl
alcohol poisoning are caused by toxic metabolites and devel-
op after a latent period of about 12 to 24 hours or longer will
concomitant alcohol consumption. The outstanding feature;
of poisoning are metabolic acidosis with rapid, shallow
breathing, visual disturbances which often proceed to irre
versible blindness, and severe abdominal pain. Other symp
toms include headache, gastro-intestinal disturbances, pain if
the back and extremities, and coma which in severe cases ma)
terminate in death due to respiratory failure or, rarely, to cir
culatory collapse. Mania and convulsions occasionally occur
Individual response to methyl alcohol varies widely. Inges
tion of 30 mL is considered to be potentially fatal.
Absorption of methyl alcohol through the skin or inhalation
of the vapour may also lead to toxic systemic effects.
References to the adverse effects of methyl alcohol.
Treatment of Adverse Effects
Recent ingestion of methyl alcohol should be treated by gas
trie lavage; activated charcoal may be administered. Metabol
ic acidosis should be corrected immediately with intravenou
sodium bicarbonate. Treatment with alcohol, which delay
the oxidation of methyl alcohol to its toxic metabolites
should also be initiated, the dosage being adjusted to achieve
and maintain a blood-alcohol concentration of I to 2 mg pe
mL. An oral dose of about 50 g (equivalent to 150 mL o
40% v/v alcohol) for an adult of around 70 kg body-weigh
has been suggested: the alcohol should be well diluted before
administration. If required, an alcohol infusion may then be
given for which the following doses have been used: 120 mL
of 10% alcohol or 250 mL of 5% alcohol per hour. For alco-
holic patients or those with induced liver enzymes, the dose
of alcohol should be increased accordingly. Suggested doses
arc 145 mL of 10% alcohol or 300 mL of 5% alcohol per
hour.
Haemodialysis may be indicated to increase the removal of
methyl alcohol and its toxic metabolites. Peritoneal dialysis
has been used but is less efficient. Some authorities recom-
mend initiation of haemodialysis if the amount of methyl al-
cohol ingested exceeds 30 g (equivalent to about 40 mL), if
the blood-methyl alcohol concentration is greater than 500 ng
per mL, or if severe metabolic acidosis or visual complica-
tions develop. If haemodialysis is used, a constant blood-al-
cohol concentration may be ensured cither by increasing the
alcohol infusion rate or by addition of alcohol to the dialysate
fluid. Treatment should not be discontinued prematurely
since oxidation and excretion of methyl alcohol may continue
for several days; patients should, therefore, be closely ob-
served and monitored. Suitable supportive treatment should
be carried out as required.
References indicating blood-formate concentrations to be a
better predictor of the severity of methyl alcohol poisoning
than concentrations of methyl alcohol.
Pharmacokinetics
Methyl alcohol is readily absorbed from the gastro-intestinal
tract and distributed throughout the body fluids. It may also
be absorbed by inhalation or through large areas of skin. Ox-
idation by alcohol dehydrogenase with formation of formal-
dehyde and formic acid takes place mainly in the liver and
also in the kidneys. These metabolites are thought to be large-
ly responsible for the characteristic symptoms of methyl alco-
hol poisoning. Metabolism is much slower than for ethyl
alcohol, which competitively inhibit the metabolism of me-
thyl alcohol. Oxidation and excretion may continue for sever-
al days after ingestion. Elimination of unchanged methyl
alcohol via the lungs and in the urine is a minor route of ex-
cretion.
Uses
Methyl alcohol is used as a pharmaceutical and industrial sol-
vent. It is also used as 'wood naphtha' to denature alcohol in
the preparation of industrial methylated spirits. Methyl alco-
hol is also used as an extraction solvent in food processing.
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