All of the following are true about methanol poisoning except: (AIIMS November 2013, May 2013)
**Core Concept**
Methanol poisoning is a toxic condition resulting from the ingestion of methanol, a low-molecular-weight alcohol. It affects multiple organs, particularly the central nervous system, kidneys, and eyes. Methanol is metabolized by alcohol dehydrogenase to form formaldehyde, which is then converted to formic acid by aldehyde dehydrogenase.
**Why the Correct Answer is Right**
Methanol poisoning is characterized by a delay in its toxic effects due to the slow metabolism of methanol to its toxic metabolites. Formaldehyde is highly toxic but is quickly converted to formic acid, which is responsible for the severe metabolic acidosis, visual disturbances, and neurological symptoms observed in methanol poisoning. The primary treatment involves the use of fomepizole, an alcohol dehydrogenase inhibitor, to prevent the formation of toxic metabolites.
**Why Each Wrong Option is Incorrect**
**Option A:** Methanol is a central nervous system depressant.
* This statement is incorrect because methanol is a central nervous system stimulant, not a depressant. Its toxic metabolites, particularly formic acid, are responsible for the central nervous system depression observed in methanol poisoning.
**Option B:** Methanol is metabolized to formaldehyde by alcohol dehydrogenase.
* This statement is correct. Methanol is indeed metabolized to formaldehyde by alcohol dehydrogenase, which is the first step in its metabolism.
**Option C:** Methanol poisoning is characterized by a rapid onset of symptoms.
* This statement is incorrect. Methanol poisoning is characterized by a delay in its toxic effects due to the slow metabolism of methanol to its toxic metabolites.
**Option D:** Fomepizole is used to treat methanol poisoning by inhibiting the metabolism of methanol.
* This statement is correct. Fomepizole is an alcohol dehydrogenase inhibitor that is used to treat methanol poisoning by preventing the formation of toxic metabolites.
**Clinical Pearl / High-Yield Fact**
Methanol poisoning is often mistaken for ethanol intoxication due to the similar presentation of central nervous system depression. However, the key difference lies in the delayed onset of symptoms and the presence of visual disturbances, which are characteristic of methanol poisoning.
**Correct Answer: A. Methanol is a central nervous system depressant.**