🧪 Toxic Alcohols and Their Poisoning
🔷 1. Types of Toxic Alcohols
|
Alcohol |
Source |
Key Toxin (after metabolism) |
|
Ethanol |
Alcoholic beverages |
Acetaldehyde (mildly toxic) |
|
Methanol |
Windshield washer fluid, paint thinner |
Formic acid |
|
Ethylene glycol |
Antifreeze, coolant, de-icing agents |
Glycolic & oxalic acid |
|
Isopropanol |
Rubbing alcohol, hand sanitizer |
Acetone (non-acidic) |
🔷 2. Key Pathophysiology
|
Alcohol |
Metabolized By |
Key Toxic Effects |
|
Methanol |
ADH → Formaldehyde → Formic acid |
Retinal toxicity, severe acidosis |
|
Ethylene glycol |
ADH → Glycolic acid → Oxalic acid |
Renal failure, crystals, CNS depression |
|
Isopropanol |
ADH → Acetone |
CNS depression, no acidosis |
|
Ethanol |
ADH → Acetaldehyde |
Hypoglycemia, sedation (rarely severe toxicity unless chronic use or binge) |
🔷 3. Clinical Features by Alcohol Type
|
Feature |
Methanol |
Ethylene Glycol |
Isopropanol |
Ethanol |
|
Onset |
6–24 h post ingestion |
1–12 h |
Rapid |
Rapid |
|
Neuro |
Visual loss, coma |
Seizures, coma |
Coma, sedation |
Ataxia, drowsiness |
|
Eye signs |
Snowfield vision, blurry |
Normal |
Normal |
Normal |
|
Kidney |
Often normal early |
Acute renal failure, hematuria |
Normal |
Possible ATN in chronic alcoholics |
|
Smell |
Odorless |
Odorless |
Fruity/acetone |
Alcohol smell |
|
Metabolic acidosis |
Severe, with ↑ anion gap |
Severe, ↑ anion gap |
No acidosis |
Mild or none |
|
Osmolar gap |
↑↑ |
↑↑ |
↑↑ |
↑ |
|
Crystals in urine |
No |
Calcium oxalate |
No |
No |
🔷 4. Key Labs & Diagnosis
- ABG: Severe metabolic acidosis (except isopropanol)
- Anion gap (AG) = Na – (Cl + HCO₃)
- Osmolar gap (OG) = Measured Osm – Calculated Osm
- Osm Gap >10 = Suggestive of toxic alcohol
- Calculated Osm = 2[Na] + Glucose/18 + BUN/2.8 + Ethanol/4.6
- Urine:
- Oxalate crystals (EG)
- Formic acid (Methanol – not routinely measurable)
- CT brain: Bilateral putaminal necrosis (Methanol)
🔷 5. Management Principles (ABCDE + ADH blockade)
🅰️ Airway, Breathing, Circulation
- Secure airway for GCS <8
- Treat seizures, shock, electrolyte imbalance
🧪 Antidotes
🔹 1. Fomepizole (1st line)
- Blocks alcohol dehydrogenase
- Dose: 15 mg/kg IV loading, then 10 mg/kg q12h
- Use in methanol & ethylene glycol
🔹 2. Ethanol (IV/oral)
- Competes with methanol/EG for ADH
- IV: 10% ethanol infusion to maintain serum 100–150 mg/dL
- Monitor blood ethanol level
🔸 Note: Not useful for isopropanol
💉 Hemodialysis Indications (Methanol / EG)
- Severe metabolic acidosis (pH <7.25)
- End-organ damage (AKI, visual loss)
- High methanol/EG level (>50 mg/dL)
- Clinical deterioration
💊 Supportive Measures
- IV bicarbonate for acidosis
- Thiamine + pyridoxine (in EG poisoning – aid alternative metabolism)
- Folinic acid or folic acid (enhances formic acid metabolism in methanol)
🔷 6. Mnemonic – M-E-I for Toxic Alcohols
- M – Methanol → “M for Muddy vision”
- E – Ethylene glycol → “E for Edematous kidneys”
- I – Isopropanol → “I for Intoxicated look with no acidosis”
🔷 8. Key MCQ Points for Exams
- Pulse oximetry can be falsely normal
- Osmolar gap ↑ in all 3 but not always reliable
- Methanol – vision, EG – kidneys, Isopropanol – sedation without acidosis
- Fomepizole is preferred antidote; ethanol is an alternative
- Methanol poisoning can mimic stroke (basal ganglia necrosis)