Review Question - QID 105649

This patient is most likely suffering from methanol poisoning given his intoxication, blurry vision, and anion gap acidosis. The most appropriate initial step in management is to administer fomepizole (which inhibits alcohol dehydrogenase).

Methanol is metabolized by alcohol dehydrogenase (ADH) to formaldehyde, which is then converted to formic acid by aldehyde dehydrogenase. Formic acid is toxic to the optic nerve, leading to visual changes and blindness with as little as 30 mL ingested. Early formation of formic acid leads to metabolic acidosis; however, formic acid also binds to cytochrome oxidase and inhibits oxidative phosphorylation, leading to a later formation of a lactic acidosis. Any patient presenting with suspected methanol ingestion should promptly be started on fomepizole to stop the formation of toxic byproducts (formic acid) followed by dialysis.

Incorrect Answers:
Answer 1: Glutathione formation is the mechanism of N-acetylcysteine which is the antidote for acetaminophen overdose which is a hepatotoxic agent.

Answer 3: Inhibition of aldehyde dehydrogenase is not an enzyme that is inhibited in the treatment of methanol ingestion. It is one of the enzymes in the pathway which forms the toxic byproduct formic acid.

Answer 4: Muscarinic antagonism is the mechanism of atropine which may be indicated in the treatment of a cholinergic toxidrome (secondary to agents such as organophosphates or sarin). A cholinergic toxidrome presents with urinary incontinence, diarrhea, bronchorrhea, bronchospasm, and bradycardia.

Answer 5: Removal via dialysis is the ultimate management of methanol intoxication after fomepizole has been given to inhibit alcohol dehydrogenase.

Bullet Summary:
The most appropriate initial step in management in methanol intoxication is to administer fomepizole which inhibits alcohol dehydrogenase.