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Context-Sensitive Half-Time — FRCA Primary MCQ

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ModeratePharmacology - General PrinciplesContext-Sensitive Half-TimeFRCA Primary

In intravenous pharmacokinetics, which statement best defines the context-sensitive half-time?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: D — The time for plasma concentration to decrease by 50% after stopping an infusion of a given duration

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

D is correct. Context-sensitive half-time is the time required for the blood or plasma concentration of a drug to decrease by 50% after an infusion is stopped. The “context” is the preceding infusion duration. It incorporates redistribution between pharmacokinetic compartments as well as elimination, so it may change substantially as an infusion is prolonged and cannot reliably be inferred from terminal elimination half-life. Option A describes an effect-site decrement, which additionally depends on plasma–effect-site equilibration. Option B describes terminal elimination half-life. Option C omits the defining infusion context and instead concerns a bolus. Option E concerns drug accumulation towards steady state rather than offset after stopping administration.

Reference: Bailey JM. Context-sensitive half-times: what are they and how valuable are they in anaesthesiology? Clinical Pharmacokinetics. 2002;41(11):793–799. https://pubmed.ncbi.nlm.nih.gov/12190329/