Nitrous oxide expansion of gas spaces — FRCA Primary MCQ
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Correct answer: A — Inactivation of vitamin B12-dependent methionine synthase
The best answer is “Inactivation of vitamin B12-dependent methionine synthase”. Nitrous oxide oxidises the cobalt centre of vitamin B12 and can inactivate the B12-dependent enzyme methionine synthase. Repeated or prolonged exposure can therefore cause neurological and haematological toxicity. It does not act through cholinesterase, sodium-channel, acetylcholinesterase or carbonic-anhydrase mechanisms.
Reference: MHRA, Nitrous oxide: neurological and haematological toxic effects: https://www.gov.uk/drug-safety-update/nitrous-oxide-neurological-and-haematological-toxic-effects