Adverse effects of Janus kinase inhibitors with relevance for daily practice in dermatology.

Used since 2011 in the USA and 2012 in the EU, Janus kinase inhibitors (JAKi) are gaining increasing acceptance as a treatment for dermatological diseases such as atopic dermatitis, psoriasis, psoriatic arthritis, alopecia areata, chronic hand eczema and vitiligo. Knowledge of their mechanism of action and potential side effects is necessary for a safe and effective use. Their short half-life requires daily administration, enables good controllability and is appreciated by many patients due to the rapid onset of action and the absence of subcutaneous or intravenous injections. Common side effects are upper respiratory tract infections as well as varicella zoster virus reactivations. Serious infections can occur in rare cases, which may take a problematic course. An increased risk of cardiovascular events has been described in certain JAKi, so alternative treatment should be preferred in patients at cardiovascular risk. In studies on rheumatoid arthritis, an increased incidence of malignancies (bronchial carcinoma, lymphoma) was observed with tofacitinib. JAKi have also been associated with more aggressive progression of epithelial skin tumors. Animal studies indicate teratogenic effects during pregnancy. Older patients and those at increased risk should only receive JAKi after careful risk-benefit assessment. Appropriate preliminary examinations and regular laboratory monitoring are necessary to ensure safe therapy.