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Filgotinib Selectivity — SCE Rheumatology MCQ

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ModerateRheumatology PharmacologyFilgotinib SelectivitySCE Rheumatology

A 55-year-old woman with rheumatoid arthritis asks how filgotinib differs mechanistically from other oral Janus kinase inhibitors. Which statement most accurately describes filgotinib's kinase selectivity?

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

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Correct answer: A — It preferentially inhibits JAK1, with over fivefold biochemical selectivity versus JAK2, JAK3 and TYK2.

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

Filgotinib is an ATP-competitive, reversible JAK inhibitor that preferentially inhibits JAK1. In biochemical assays, it has more than fivefold greater potency for JAK1 than for JAK2, JAK3 or TYK2. By contrast, option C more closely describes baricitinib, which inhibits JAK1 and JAK2 with similar isolated-enzyme potency. Filgotinib is not a JAK2-, JAK3- or TYK2-specific inhibitor, excluding A, D and E. This biochemical selectivity should not be interpreted as demonstrating a superior clinical safety profile: MHRA risk-minimisation measures for major cardiovascular events, malignancy, venous thromboembolism, serious infection and mortality apply across the inflammatory-disease JAK-inhibitor class.

Reference: Electronic Medicines Compendium. Jyseleca 100 mg film-coated tablets, Summary of Product Characteristics, section 5.1 Pharmacodynamic properties. Updated 18 July 2025. https://www.medicines.org.uk/emc/product/11809/smpc