Remifentanil Context-Sensitive Half-Time — FRCA Primary MCQ

Correct answer: D — Remifentanil

Remifentanil has the shortest context-sensitive half-time, approximately 3–4 minutes, which changes little with increasing infusion duration. It contains an ester linkage and is rapidly hydrolysed by non-specific blood and tissue esterases to an essentially inactive metabolite. Its offset therefore remains rapid after a 4-hour infusion. Alfentanil is the most plausible distractor because it is relatively short acting, but its context-sensitive half-time lengthens substantially during prolonged infusion. Fentanyl and sufentanil redistribute into peripheral compartments and accumulate during infusion, producing longer context-sensitive half-times. Morphine also has a much slower offset and an active metabolite; it is not an ultra-short-acting infusion opioid. Context-sensitive half-time is the time required for plasma concentration to fall by 50% after stopping an infusion of a specified duration.

Reference: Kapila A et al. Measured context-sensitive half-times of remifentanil and alfentanil. Anesthesiology. 1995;83:968–975. https://pubmed.ncbi.nlm.nih.gov/7486182/