Methanol (methyl alcohol) poisoning causes blindness and metabolic acidosis through which specific toxic metabolite?
- A Acetaldehyde — the same metabolite responsible for ethanol's flushing reaction
- B Lactic acid — from methanol-induced mitochondrial uncoupling
- C Formic acid — produced from formaldehyde via alcohol dehydrogenase and aldehyde dehydrogenase pathways ✓
- D Oxalic acid — which chelates calcium and causes hypocalcaemic tetany
Explanation
Methanol is metabolised by alcohol dehydrogenase (ADH) to formaldehyde, then by aldehyde dehydrogenase (ALDH) to formic acid. Formic acid inhibits mitochondrial cytochrome c oxidase (Complex IV), disrupting oxidative phosphorylation in retinal ganglion cells and the optic nerve, causing selective retinal toxicity and blindness. It also causes a high-anion-gap metabolic acidosis. Treatment with ethanol (competitive ADH inhibitor) or fomepizole (ADH inhibitor) blocks methanol metabolism. Haemodialysis removes methanol and formate directly. Oxalic acid is the toxic metabolite of ethylene glycol poisoning.
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.