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Drug Interaction — SCE Medical Oncology MCQ

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HardOncological EmergenciesDrug InteractionSCE Medical Oncology

A patient taking capecitabine is prescribed brivudine for herpes zoster and develops severe diarrhoea, mucositis, neutropenia and encephalopathy. Which interaction explains this potentially fatal toxicity?

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

Reveal the answer and explanation

Correct answer: B — Brivudine inhibits DPD, markedly reducing fluoropyrimidine catabolism and increasing systemic fluorouracil exposure

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

E is correct. Brivudine and related analogues inhibit dihydropyrimidine dehydrogenase, the rate-limiting enzyme for fluoropyrimidine catabolism, so coadministration can cause profound and fatal capecitabine or 5-FU toxicity. The UK SmPC contraindicates concurrent or recent brivudine and requires at least four weeks between stopping brivudine and starting capecitabine; brivudine can begin 24 hours after the last capecitabine dose. A invokes the wrong direction and enzyme. B wrongly proposes CYP induction. C invents a renal interaction. D is not the clinically important mechanism. Capecitabine must be stopped and severe toxicity managed urgently.

Reference: Capecitabine UK Summary of Product Characteristics: https://www.medicines.org.uk/emc/product/14545/smpc