Filgotinib, a novel JAK1-preferential inhibitor for the treatment of rheumatoid arthritis: An overview from clinical trials

Abstract In the treatment of rheumatoid arthritis (RA), Janus kinase inhibitors (jakinibs) represent an emerging class of targeted therapies in addition to biologics. The number of jakinibs has been growing and as of 2020, filgotinib was the latest jakinib to enter the international market for treating RA. Filgotinib has demonstrated preferential inhibition of JAK1-dependent cytokine signaling in in vitro assays. It has been evaluated in the DARWIN (phase 2) and FINCH (phase 3) series of clinical studies for treating patients with moderately-to-severely active RA. Filgotinib received regulatory approval in Japan and Europe in September 2020, while in August 2020 the United States Food and Drug Administration requested additional data from two ongoing clinical studies assessing the potential impact of filgotinib on sperm parameters. This article will review the pharmacological properties, efficacy, and safety of filgotinib as demonstrated in clinical studies. Expert opinion will be provided on jakinibs for RA treatment from the viewpoints of basic research and clinical practice.