Methanol

Question 1

Methanol is obtained from .

Answer 1

distillation of wood

Question 2

Methanol is Found at home, in the workplace used as:

Answer 2

Antifreeze (window washer fluid)
Laboratory chemical 
Ethanol denaturation
Solvent
Fuel source

Question 3

Mechanism of toxicity

Answer 3

• Methanol itself not toxic.
• Formaldehyde is very toxic, but very rapidly metabolized to formic acid.
• Formic acid responsible for the toxicity related to methanol ingestions
• Formic acid inhibits cytochrome oxidase resulting in cellular hypoxia and anaerobic metabolism resulting in lactic acidosis.

Question 4

SIGNS AND SYMPTOMS

Answer 4

Onset of manifestation: Delayed ( 12-36 hr) due to slow metabolism of methanol to the toxic metabolites.

CNS – Drowsiness progressing to coma, Convulsions
EYE - Blurred vision, photophobia, dilated non-reactive pupils,
Sudden loss of vision or complete blindness due to optic neuritis may occur.
GIT - Nausea, vomiting
CARDIAC - Tachycardia, hypertension progressing To hypotension and shock (what is type of shock???)
RESPIRATORY - Tachypnea

Question 5

INVESTIGATIONS

Answer 5

1. ABG and electrolytes to monitor acidosis, respiratory depression and hyperkalemia
2. Random blood sugar
3. Kidney function tests
4. Methanol blood level: Levels above 25mg/dl are indications for antidotes and hemodialysis.
5. ECG and cardiac monitoring to rule out ischemia and dysrhythmias
6. Fundus examination and visual evoked potential: Initial and serial examinations are essential to assess optic nerve affection

Question 6

TREATMENT

Answer 6

I. Emergency measures: ABCD
-Oxygen, Airway, Breathing, Circulation support
-Control acidosis (if pH is less than 7.15) and hyperkalemia by slow infusion of Na Bicarbonate. In addition it keeps formic acid in its anionic form to decrease its entry to CNS.
II. Gut decontamination and elimination
-Gastrointestinal decontamination is rarely indicated because of its rapid absorption and limited binding to AC.
-Hemodialysis is indicated
1-if methanol level exceeds 25-30mg/dl, in
2-acidosis refractory to treatment or
3-in renal failure.

Question 7

TREATMENT (Cont.)

Answer 7

III. Antidotes
a- Ethyl alcohol 1gm/kg followed by 0.5gm/kg/4 h to maintain blood ethanol at 100mg/dl.( see the attached note to the slide)
b- 4-methylpyrazole (4-MP, Fomepizole®)
Both ethyl alcohol and 4-MP compete with methanol for alcohol dehydrogenase enzyme.
c- Folinic acid: It helps oxidation of accumulated formates
IV. Symptomatic treatment
Diazepam or other anticonvulsant for convulsions
Steroids are early indicated for optic neuritis or later for cerebral edema.