Ethyl Alcohol
Ethyl alcohol, commonly known as ethanol, is a widely used central nervous system (CNS) depressant. It is present in alcoholic beverages and also used in medical practice as an antiseptic and antidote in methanol poisoning.
Chemically, ethanol is a small organic compound with the formula:
C₂H₅OH
Mechanism of Action of Ethanol
Ethanol primarily acts on the central nervous system.
1. GABA Enhancement
Enhances GABA-A receptor activity
Increases chloride influx
Produces sedation and anxiolysis
2. NMDA Receptor Inhibition
Inhibits glutamate (excitatory neurotransmitter)
Causes memory impairment
3. Dopamine Release
Activates reward pathway
Responsible for addiction
Pharmacokinetics of Ethanol
Absorption
Rapidly absorbed from stomach and small intestine
Food delays absorption
Distribution
Distributed throughout total body water
Crosses blood-brain barrier
Metabolism (Liver)
Ethanol → (Alcohol dehydrogenase) → Acetaldehyde
Acetaldehyde → (Aldehyde dehydrogenase) → Acetic acid
Acetic acid → CO₂ + Water
Effects of Ethanol (Dose Dependent)
| Blood Alcohol Level | Clinical Effect |
|---|---|
| 0.02% | Mild euphoria |
| 0.05% | Impaired judgment |
| 0.1% | Ataxia |
| 0.2% | Slurred speech |
| >0.3% | Coma |
| >0.4% | Respiratory depression |
Medical Uses of Ethanol
Antiseptic (70% solution)
Antidote for methanol poisoning
Solvent in pharmaceutical preparations
Adverse Effects
Acute
CNS depression
Hypoglycemia
Gastritis
Respiratory depression
Chronic
Liver cirrhosis
Fatty liver
Peripheral neuropathy
Wernicke-Korsakoff syndrome
Methyl Alcohol (Methanol)
Paint removers
Antifreeze
Industrial solvents
Chemical formula: CH₃OH
Why Methanol is Dangerous
Methanol itself is not very toxic, but its metabolites are extremely harmful.
Metabolism of Methanol
Methanol → (Alcohol dehydrogenase) → Formaldehyde
Formaldehyde → (Aldehyde dehydrogenase) → Formic acid
Formic acid causes:
Severe metabolic acidosis
Optic nerve damage
Blindness
Death
Clinical Features of Methanol Poisoning
Early Symptoms (6–12 hours)
Headache
Dizziness
Nausea
Vomiting
Late Symptoms
Blurred vision (“snowfield vision”)
Photophobia
Severe metabolic acidosis
Coma
Why Vision is Affected?
Formic acid accumulates in optic nerve →
Mitochondrial dysfunction →
Optic nerve necrosis →
Permanent blindness
Diagnosis
High anion gap metabolic acidosis
Elevated osmolar gap
Blood methanol level
Arterial blood gas (ABG)
Treatment of Methanol Poisoning
1. Fomepizole (First Line)
Inhibits alcohol dehydrogenase
Prevents toxic metabolite formation
2. Ethanol (Alternative)
Competes for alcohol dehydrogenase
3. Sodium Bicarbonate
Corrects metabolic acidosis
4. Hemodialysis
Removes methanol and formic acid
Key Differences Between Ethanol and Methanol
| Feature | Ethanol | Methanol |
|---|---|---|
| Formula | C₂H₅OH | CH₃OH |
| Toxicity | CNS depressant | Highly toxic |
| Toxic Metabolite | Acetaldehyde | Formic acid |
| Causes Blindness | No | Yes |
| Antidote | Not required | Fomepizole/Ethanol |
Exam Important Points
Methanol poisoning causes high anion gap metabolic acidosis
Blindness is due to formic acid toxicity
Ethanol enhances GABA activity
Chronic alcohol use causes liver cirrhosis
Conclusion
Ethyl alcohol (ethanol) acts primarily as a central nervous system depressant and has both medical uses and abuse potential. In contrast, methyl alcohol (methanol) is a dangerous toxic compound whose metabolites can cause metabolic acidosis, blindness, and death. Understanding their metabolism and mechanisms is crucial for early diagnosis and life-saving treatment.