1) Methanol is toxic to humans when ingested and is sometimes used as an ethanol substitute by alcoholics. It is metabolized to formaldehyde and formic acid which cause metabolic acidosis, blindness, and can be fatal. 2) The toxic effects of methanol occur after a latent period of 30 hours as it is slowly metabolized. Symptoms include vision loss, seizures, coma and death. Treatment focuses on preventing further metabolism using fomepizole or ethanol and enhancing excretion through hemodialysis. 3) Diagnosis is based on history of ingestion and laboratory findings showing a large osmolar or anion gap metabolic acidosis. Levels of methanol, formate or a

1. Methanol toxicity
Dr. Hein Yarzar Aung
Consultant Physician
Medical Unit 1
Yangon General Hospital

2. Introduction
• Methanol (wood alcohol)
– a common ingredient in many solvents,
windshield-washing solutions, duplicating fluids,
and paint removers
– sometimes is used as an ethanol substitute by
alcoholics
– its metabolic products may cause
• metabolic acidosis, blindness, and death after a
characteristic latent period of 30 hours

3. Mechanism of toxicity
• slowly metabolized by alcohol dehydrogenase
to formaldehyde
• subsequently by aldehyde dehydrogenase to
formic acid (formate)
– systemic acidosis is caused by both formate and
lactate
– blindness is caused primarily by formate

4. Pharmacokinetics
• readily absorbed and quickly distributed to the
body water
• metabolized slowly by alcohol
• "half-life" ranges from 1 to 24 hours
• Only about 3% is excreted unchanged by the
kidneys, and less than 10-20% through the breath
• Formate: half-life ranges from 3-20 hours; during
dialysis the half-life decreases to 1-2.6 hours

5. Toxic dose
• The fatal oral dose of methanol is 30-240 mL
(20-150 g)
• The minimum toxic dose is approximately 100
mg/kg

6. Clinical presentation
• In the first few hours after ingestion
– inebriation and gastritis
– acidosis is not usually present (metabolism to
toxic products has not yet occurred)

7. • After a latent period of up to 30 hours
– severe anion gap metabolic acidosis
– visual disturbances ( may occur within 6 hours ),
blindness, seizures, coma, acute renal failure with
myoglobinuria, and death
– fundoscopic examination - optic disc hyperemia,
venous engorgement, peripapilledema, and retinal
or optic disc edema
– The latent period is longer when ethanol has been
ingested concurrently with methanol

8. Diagnosis
• usually is based on the history, symptoms
• stat methanol levels are rarely available
• Calculation of the osmolar and anion gaps
(see Serum osmolality and osmolar gap)
– A large anion gap not accounted for by elevated
lactate suggests possible methanol (or ethylene
glycol) poisoning, because the anion gap in these
cases is mostly nonlactate

9. • Specific levels
– 1. Serum methanol level
• higher than 20 mg/dL – toxic
• higher than 40 mg/dL - very serious
• After the latent period, a low or nondetectable
methanol level does not rule out serious intoxication in
a symptomatic patient because all the methanol may
already have been metabolized to formate

10. – 2. Elevated serum formate concentrations
• may confirm the diagnosis and are a better measure of
toxicity
• but formate levels are not widely available

11. – 3. Other useful laboratory studies
• include electrolytes (and anion gap), glucose, BUN,
creatinine, serum osmolality and osmolar gap, arterial
blood gases, ethanol level, and lactate level

12. Treatment
• Emergency and supportive measures
– 1. Maintain an open airway and assist ventilation
if necessary
– 2. Treat coma if they occur
– 3. Treat metabolic acidosis with intravenous
sodium bicarbonate
• Correction of acidosis should be guided by arterial
blood gases

13. Specific drugs and antidotes
• 1. Administer fomepizole or ethanol ( to saturate
the enzyme alcohol dehydrogenase and prevent
the formation of methanol's toxic metabolites )
• Indications
– a. A history of significant methanol ingestion when
methanol serum levels are not immediately available
– b. Metabolic acidosis (arterial pH < 7.3, serum
bicarbonate < 20 mEq/L) and an osmolar gap greater
than 10 mOsm/L not accounted for by ethanol
– c. methanol blood concentration greater than 20
mg/dL.

14. Ethanol for Methanol

15. • Ethanol
– 40%
– 120 ml stat
– 12 ml hrly for non – drinker
– 24 ml hrly for chronic drinker
– Until serum methanol level < 20 mg/dl

16. • 2. Folic or folinic acid
– may enhance the conversion of formate to carbon
dioxide and water
– 1 mg/kg (up to 50 mg) IV or PO every 4 hours

17. Management

18. • C. Decontamination
– Aspirate gastric contents if this can be performed
within 30-60 minutes of ingestion
– Activated charcoal is not likely to be useful
because the effective dose is very large and
methanol is absorbed rapidly from the GI tract

19. • D. Enhanced elimination
– Hemodialysis rapidly removes both methanol
(half-life reduced to 3-6 hours) and formate
– Indications
• a. Suspected methanol poisoning with significant
metabolic acidosis
• b. Visual abnormalities
• c. Renal failure
• d. An osmolar gap greater than 10 mOsm/L or a
measured serum methanol concentration greater than
50 mg/dL

20. • E. Endpoint of treatment
– Dialysis, fomepizole, or ethanol should be
continued until the methanol concentration is less
than 20 mg/dL
– and the osmolar and anion gaps are normalized

21. • Thank you!!