Variation in Hematological Parameters Associated with Janus Kinases 1 and 2 Inhibition in a Patient with Atopic Dermatitis

Baricitinib, janus kinase (JAK) 1/2 inhibitor, can significantly improve the patients with moderate to severe atopic dermatitis (AD). However, the concerns about its hematological safety have raised. A 57-year-old man with severe AD started taking baricitinib due to ineffectiveness and side effects of conventional treatments. After 16 weeks, hemoglobin level decreased to 7.5 g/dL. He started taking folate and multivitamin supplements for anemia with baricitinib suspension, and hemoglobin level increased after 2 weeks. Baricitinib affects hemoglobin levels and other hematological parameters by inhibiting the action of erythrocyte production, which is promoted by JAK2 signaling. When treating AD patients with baricitinib, periodic blood test is required to confirm the occurrence of hematological abnormalities.