Paper I — 2015 September (Supplementary) (2010 Scheme) — Q9
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Paper I
2015 September (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Rationale for use of ethanol in methanol poisoning
Q91 marksShort Answers
Answer
Methanol itself is relatively non-toxic, but it is metabolized by alcohol dehydrogenase to formaldehyde and then to formic acid, which are responsible for the severe toxicity (metabolic acidosis, ocular toxicity/blindness). Ethanol has a much higher affinity for alcohol dehydrogenase than methanol, so administering ethanol competitively saturates the enzyme, preventing/slowing the conversion of methanol into its toxic metabolites, allowing unmetabolized methanol to be excreted renally while toxicity is limited. (Fomepizole, a direct alcohol dehydrogenase inhibitor, is now the preferred antidote where available.)
