AbstractBackgroundAtopic dermatitis (AD) is associated with an increased risk for viral infections including those caused by herpes simplex virus and varicella zoster virus.ObjectivesThis study examined treatment‐emergent (TE) herpes simplex infection including eczema herpeticum (EH), and herpes zoster (HZ), in adult patients with AD receiving ≥1 dose of baricitinib (BARI), an oral selective inhibitor of Janus kinase 1/2.MethodsWe evaluated data from six double‐blinded, randomized, placebo‐controlled (PC) trials and two long‐term extension studies, within three analysis sets: PC, 2–4‐mg BARI extended and All‐BARI‐AD. Frequency, incidence rate (IR)/100 person‐years (PYs) and clinical characteristics of TE‐herpes simplex, EH and HZ were reported.ResultsIn the All‐BARI‐AD dataset (n = 2531; 2247 PYs), herpes simplex was reported in 8.9% of patients (n = 224; IR = 10.3). Most herpes simplex events were rated as mild or moderate (93.3%), rarely led to permanent discontinuation (2.2%) and presented mostly as oral/perioral herpes simplex (51.3%). TE‐EH occurred at a low frequency (All‐BARI‐AD 1.7% n = 43; IR = 2.0) and were reported in 0.5%, 0.2% and 1.4% of patients receiving placebo, 2‐mg or 4‐mg BARI respectively. In the All‐BARI‐AD dataset, most events were investigator‐rated as mild/moderate (79.1%), affected ≤2% of the body surface area (74.2%) and occurred as single events (88.4%). Serious TE‐EH (n = 11) occurred exclusively in patients with poor disease control (vIGA‐AD™ score ≥3) at infection onset. TE‐HZ was reported in 2.1% of BARI patients (n = 53; IR = 2.3), without a dose relationship during the PC period (IR = 2.7 and IR = 0.0) or the extended dataset (IR = 3.7 and IR = 1.7) for 2‐ or 4‐mg BARI respectively.ConclusionsTE‐herpes simplex was common, while occurrence of EH was uncommon. Most events of EH were localized with involvement of a small BSA and were linked to poor disease control. Events of HZ were rare in the PC dataset and without a dose dependent increase in frequency.