The infection risks of JAK inhibition.

INTRODUCTION Janus Kinase inhibitors (JAKi) have shown to be highly effective in the treatment of immune-mediated inflammatory diseases, and several drugs in this class have been approved in recent years. As with all immunomodulatory therapies, careful assessment of any treatment-associated infection risk is essential to inform clinical decision-making. AREAS COVERED We summarise the current literature on infection rates among the licensed JAKi using published phase II/III trial results as well as post-licensing and registry data. EXPERT OPINION Data currently available for the licensed JAKi show an increased risk of infection across the class compared to placebo, most commonly affecting the respiratory and urinary tracts, nasopharynx and skin. This risk is dose-dependent, but similar at the licensed JAKi doses to that seen with biologic therapies. The risk is compounded by other risk factors for infection such as age and steroid co-prescription. Herpes zoster reactivation is more common with JAKi compared to other targeted immune modulation, making screening for varicella exposure and judicious vaccination in appropriate cohorts an advisable strategy. Crucially, these small risk increases must be balanced against the known harms (including infection) of uncontrolled autoimmune disease. JAKi are a safe and potentially transformative treatment when used for appropriately selected patients.