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JAK Inhibitor Effects — SCE Rheumatology MCQ

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ModerateRheumatoid ArthritisJAK Inhibitor EffectsSCE Rheumatology

A 45-year-old woman with rheumatoid arthritis starts baricitinib 4 mg once daily. Her baseline lipid profile, creatine phosphokinase (CPK) and thyroid-stimulating hormone are normal. Twelve weeks later, her total and LDL cholesterol have increased and her CPK is 1.8 times the upper limit of normal. She has no muscle pain or weakness, takes no statin, and her hepatic transaminases remain normal. What is the most likely explanation for these laboratory findings?

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Correct answer: C — Dose-dependent baricitinib-associated increases in lipid parameters and CPK

Baricitinib causes dose-dependent increases in total cholesterol, LDL cholesterol, HDL cholesterol and CPK. Lipid elevations are typically apparent by about 12 weeks, while CPK may rise from week 4 and is usually asymptomatic and transient. The mild CPK elevation without muscle symptoms is not rhabdomyolysis. A statin interaction is excluded because she takes no statin; statin treatment can in fact reduce baricitinib-associated LDL elevation. Normal thyroid function argues against hypothyroidism, and normal baseline values with a characteristic post-treatment time course make unrelated dyslipidaemia less likely. Lipids should be assessed approximately 12 weeks after initiation and managed according to cardiovascular-risk guidance.

Reference: Electronic Medicines Compendium. Baricitinib Lilly 2 mg and 4 mg film-coated tablets, Summary of Product Characteristics, sections 4.4 and 4.8: Lipids, lipid elevations and creatine phosphokinase. Updated 3 June 2026. https://www.medicines.org.uk/emc/product/16006/smpc