Metronidazole INR Monitoring — ORE Part 1 MCQ

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

ModeratePharmacology & TherapeuticsMetronidazole INR MonitoringORE Part 1

A patient taking stable warfarin therapy is prescribed oral metronidazole for a dental infection. Which monitoring action is most appropriate?

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

Reveal the answer and explanation

Correct answer: C — Arrange increased INR monitoring

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

A is correct. Oral metronidazole can potentiate warfarin, increasing anticoagulant effect and bleeding risk. UK SmPC guidance states that prothrombin time should be monitored and that the anticoagulant dose may need reduction; the warfarin SmPC also advises increased INR monitoring when medication changes occur. SDCEP similarly advises informing the GP or anticoagulation service when an antibiotic is prescribed to a patient taking a vitamin K antagonist because INR may rise. Routine glucose, liver-function or renal-function testing is not the relevant response to this interaction. Continuing the usual INR schedule risks failing to detect excessive anticoagulation promptly.

Reference: Electronic Medicines Compendium. Metronidazole 500 mg film-coated tablets: Summary of Product Characteristics, section 4.5, 2024. https://www.medicines.org.uk/emc/product/13016/smpc