skip to main content

Warfarin vitamin K antagonism — MRCPCH TAS MCQ

Instant feedback + full explanation. One question, done properly.

ModeratePharmacologyWarfarin vitamin K antagonismMRCPCH TAS

A 14-year-old on warfarin after Fontan surgery develops a raised INR after a week of broad-spectrum antibiotics and poor intake. What is the most likely mechanism of warfarin action?

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

Reveal the answer and explanation

Correct answer: C — Inhibition of vitamin K epoxide reductase

Warfarin inhibits vitamin K epoxide reductase, reducing activation of vitamin K-dependent clotting factors. Direct thrombin inhibition describes medicines such as dabigatran, not warfarin. Antibiotics and poor intake can reduce vitamin K availability, increasing anticoagulant effect.

Reference: BNFc; Nelson Textbook of Pediatrics; RCPCH Theory examination syllabi