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ACE-Lithium — MRCPsych Paper B MCQ

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ModerateMood DisordersACE-LithiumMRCPsych Paper B

A 54-year-old man with bipolar I disorder has been stable on lithium for several years. His GP plans to start ramipril for hypertension. Which is the most important expected effect of adding ramipril?

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

Reveal the answer and explanation

Correct answer: C — Reduced lithium excretion with increased serum concentration and toxicity risk

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

B is correct. ACE inhibitors such as ramipril may reduce renal lithium excretion, causing the serum lithium concentration to rise and increasing the risk of toxicity. This can occur during prescribed maintenance treatment and is not restricted to deliberate or accidental lithium overdose. The interaction is clinically documented rather than merely theoretical. Option C describes the opposite pharmacokinetic effect, while options A and E incorrectly deny a clinically significant interaction. If an ACE inhibitor is considered necessary, the prescribers should coordinate careful monitoring of lithium levels, renal function and clinical features of toxicity, with adjustment of lithium treatment as required.

Reference: Electronic Medicines Compendium, Ramipril 5 mg capsules, Summary of Product Characteristics, section 4.5 Interaction with other medicinal products, updated 9 July 2026. https://www.medicines.org.uk/emc/product/7104/smpc