A Review of Safety Outcomes from Clinical Trials of Baricitinib in Rheumatology, Dermatology and COVID-19

Baricitinib is an oral, selective inhibitor of Janus kinase (JAK)1/JAK2 that transiently and reversibly inhibits many proinflammatory cytokines. This mechanism is a key mediator in a number of chronic inflammatory diseases; accordingly, baricitinib has been studied and approved for the treatment of several rheumatological and dermatological disorders, as well as COVID-19. This narrative review summarises and discusses the safety profile of baricitinib across these diseases, with special focus on adverse events of special interest (AESI) for JAK inhibitors, using integrated safety data sets of clinical trial data, and puts findings into context with the underlying risk in the respective disease populations, using supporting literature. We show that rates of infection with baricitinib generally reflected the inherent risk of the disease populations being treated, with serious infections and herpes zoster being more frequent in rheumatic diseases than in dermatological disorders, and herpes simplex being reported particularly in atopic dermatitis. Similarly, rates of major adverse cardiovascular events (MACE), venous thromboembolism (VTE) and malignancies were generally within or below the ranges reported for the respective disease populations, thereby reflecting the underlying risk; these events were therefore more frequent in patients with rheumatic diseases than in those with dermatological disorders, the latter of whom generally had low absolute risk. AESI were usually more common in patients with risk factors specific for each event. When a population similar to that of ORAL Surveillance was considered, the incidence rate of MACE with baricitinib was numerically lower than that reported with tofacitinib and similar to that of tumour necrosis factor inhibitors. No safety concerns were observed in hospitalised patients with COVID-19 who received baricitinib for up to 14 days. Identifying the patterns and likelihoods of AEs that occur during treatment in large groups of patients with different diseases can help the physician and patient better contextualise the benefit-to-risk ratio for the individual patient.