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NBME 20 Answers

nbme20/Block 1/Question#4

A 50-year-old man is brought to the emergency ...

Formic acid

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submitted by hayayah(525),

Methanol is toxic by two mechanisms:

First, methanol can be fatal due to its CNS depressant properties in the same manner as ethanol poisoning.

Second, in a process of toxication, it is metabolized to formic acid via formaldehyde in a process initiated by the enzyme alcohol dehydrogenase in the liver. Methanol is converted to formaldehyde via alcohol dehydrogenase (ADH) and formaldehyde is converted to formic acid (formate) via aldehyde dehydrogenase (ALDH).

Formate is toxic because it inhibits mitochondrial cytochrome c oxidase, causing hypoxia at the cellular level, and metabolic acidosis, among a variety of other metabolic disturbances.

sugaplum  Good pictograph comparing methanol, alcohol, and ethylene glycol. https://wikem.org/wiki/File:Toxic_alcohol_ingestion.JPG +4  

This is metabolic acidosis with a HIGH anion gap, this scenario involves the "M" (methanol aka formic acid) in the mnemonic "Mudpiles"

Classic scenario for methanol (as per B&B) is suspected ingestion, suicide, alcoholic.....symptoms include confusion, VISUAL symptoms, HIGH AG metabolic acidosis

Treatment: Inhibit alcohol dehydrogenase or Ethanol