Sevoflurane Degradation — FRCA Primary MCQ

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ModeratePharmacology - Inhalational AgentsSevoflurane DegradationFRCA Primary

Sevoflurane can undergo two alkaline degradation pathways after contact with carbon dioxide absorbents. Which degradation product is characteristic of the first pathway, rather than the pathway requiring a desiccated absorbent?

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Correct answer: C — Compound A (pentafluoroisopropenyl fluoromethyl ether)

Explanation lettering: E = shown as A · A = shown as E

Compound A is formed during the first alkaline degradation pathway of sevoflurane in carbon dioxide absorbents. Strong bases in the absorbent facilitate loss of hydrogen fluoride from sevoflurane, producing the vinyl ether Compound A. Its circuit concentration increases with higher absorbent temperature and sevoflurane concentration and with lower fresh-gas flow. Formaldehyde belongs to a second degradation pathway that requires desiccated absorbent and initially also produces hexafluoroisopropanol; therefore D is not correct for the specified pathway. Under extreme desiccated, high-temperature conditions, formaldehyde may undergo further reactions producing methanol, formate and carbon monoxide, making A inappropriate. B is false because degradation can occur, while E names the eliminated small molecule rather than the characteristic anaesthetic-circuit degradant.

Reference: Piramal Critical Care Limited. Sevoflurane 100% Inhalation Vapour, liquid, Summary of Product Characteristics, section 6.2 Incompatibilities, revised March 2026. https://www.medicines.org.uk/emc/product/9780/smpc