Regarding the clinical and biochemical features of methanol and ethanol poisoning, all of the following statements are correct EXCEPT:

Explanation

## Analysis of Alcohol Poisoning: Methanol vs Ethanol ### Key Biochemical Differences **Key Point:** Ethanol poisoning does NOT typically cause metabolic acidosis with an elevated anion gap. While ethanol can cause lactic acidosis in severe cases (due to impaired NAD+ metabolism), the classic presentation is CNS depression, hypoglycemia, and respiratory depression—not anion gap metabolic acidosis. ### Comparison Table: Methanol vs Ethanol Toxicity | Feature | Methanol | Ethanol | |---------|----------|----------| | **Primary metabolite** | Formic acid (toxic) | Acetaldehyde → Acetic acid (non-toxic) | | **Acid-base disturbance** | Anion gap metabolic acidosis (HIGH-YIELD) | Respiratory acidosis or lactic acidosis (not primary) | | **Target organs** | Optic nerve, basal ganglia, CNS | CNS (depression), liver | | **Onset of toxicity** | Delayed (12–24 hrs) | Rapid (minutes to hours) | | **Antidote** | Ethanol or fomepizole | Supportive care, glucose | | **Blindness risk** | YES (formic acid) | NO | ### Why Each Statement Is Correct (Except One) 1. **Methanol → anion gap acidosis:** TRUE. Formic acid (HCOOH) accumulates and dissociates, raising H^+^ and anion gap. [cite:Park 26e Ch Toxicology] 2. **Ethanol poisoning features:** PARTIALLY MISLEADING. While CNS depression and hypoglycemia are correct, **metabolic acidosis is NOT the hallmark**. Ethanol causes respiratory acidosis (from CNS depression) or lactic acidosis only in severe toxicity—NOT the classic anion gap pattern seen with methanol. 3. **Methanol → optic/basal ganglia damage:** TRUE. Formic acid is lipophilic and crosses the blood–brain barrier, causing selective necrosis of these structures. Permanent blindness is a known sequela. [cite:Robbins 10e Ch 9] 4. **Ethanol as antidote:** TRUE. Ethanol competes for alcohol dehydrogenase (ADH), blocking methanol metabolism and allowing formic acid to be excreted unchanged. This is the basis of ethanol therapy in methanol poisoning. ### Clinical Pearl **Clinical Pearl:** A patient presenting with **anion gap metabolic acidosis + visual disturbances + CNS symptoms** should raise suspicion for methanol poisoning, NOT ethanol. Ethanol causes CNS depression without the characteristic anion gap acidosis. ### High-Yield Mnemonic **Mnemonic: METHANOL = Metabolic Acidosis, Edema (cerebral), Toxicity (delayed), Harms Eyes, Anion gap, Neurodegeneration, Optic blindness, Lethal** **Mnemonic: ETHANOL = Encephalopathy, Thiamine deficiency, Hypoglycemia, Acidosis (respiratory, not anion gap), Neuropathy, Osmolar gap, Lactic acidosis (severe only)** ### Why Ethanol Doesn't Cause Anion Gap Acidosis Ethanol metabolism via ADH produces acetaldehyde and then acetic acid—neither of which accumulate to cause anion gap acidosis. The NAD+ depletion can cause lactic acidosis, but this is a secondary effect in severe poisoning, not the primary acid-base disturbance.