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Heart failure hyperkalaemia — GPhC CRA MCQ

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HardCardiovascular TherapeuticsHeart failure hyperkalaemiaGPhC CRA

A patient takes lithium once nightly at 20:00 and starts a higher dose on Friday evening. The clinic cannot sample immediately before the next 20:00 dose. Which first sampling plan still provides the standard 12-hour post-dose concentration after the advised one-week interval?

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

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Correct answer: C — Sample the following Saturday at 08:00, twelve hours after Friday’s dose

After lithium is started or its dose changes, SPS advises a first level at one week and then weekly until stable. SPS describes the standard concentration as a trough taken immediately before the next dose, 12 hours after the previous dose. With once-nightly dosing, those two phrases cannot both be literal: 08:00 is 12 hours after the 20:00 dose but is not immediately before the next 20:00 dose. The item therefore asks specifically for the standard 12-hour post-dose concentration: 08:00 on the Saturday after one full week.

Reference: NHS SPS lithium monitoring: https://www.sps.nhs.uk/monitorings/lithium-monitoring/