A 35-year-old with chronic alcoholism presents with formic acidosis, methanol level of 80 mg/dL and visual symptoms. Fomepizole is unavailable. The pharmacological rationale for using ethanol as an antidote for methanol poisoning is BEST explained by:
- A Ethanol directly neutralises formic acid in plasma
- B Ethanol induces cytochrome P450 2E1 which metabolises methanol to a less toxic compound
- C Ethanol has 10–20 times greater affinity for alcohol dehydrogenase, competitively blocking methanol oxidation to formaldehyde and formate ✓
- D Ethanol increases renal clearance of methanol by increasing GFR
Explanation
Methanol is relatively non-toxic; its metabolites—formaldehyde and formic acid (formate)—produced by alcohol dehydrogenase (ADH) are responsible for metabolic acidosis and optic nerve toxicity. Ethanol has a ~10–20 times higher affinity for ADH compared to methanol, so it competitively saturates the enzyme, blocking methanol's metabolism to toxic products while methanol is eliminated unchanged via lungs and kidneys. Fomepizole acts by a similar competitive ADH-inhibition but is more specific. Ethanol does not neutralise formic acid nor significantly enhance renal methanol clearance.
Reference: The Essentials of Forensic Medicine and Toxicology (Narayan Reddy), 34th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.