Janus kinase (JAK) inhibitors, also known as JAKi, are the latest class of synthetic (non-biologic) disease-modifying anti-rheumatic drugs (DMARDs) that have been proven effective in the treatment of multiple forms of arthritis, including psoriatic arthritis (PsA), ankylosing spondylitis (AS), and non-radiographic axial spondyloarthritis (nr-axSpA). These medications are taken orally as pills, as opposed to biologics, which are injectable.
JAK inhibitors specifically target the JAK family of enzymes, namely JAK1, JAK2, JAK3, and tyrosine kinase 2 (TYK2), each of which are involved in the initiation of the signal for a cell to make more than 60 different cytokines and growth factors.
Unlike biologics, which inhibit the effects of one single cytokine, JAKi can block the effects of multiple cytokines that are implicated in the pathogenesis (development) of many immune-mediated rheumatic diseases, including AS. They have a shorter half-life compared to biologics, meaning they are active in the body for less time, which means if they are discontinued, any side effects will disappear in a quicker fashion.
Two JAKi are FDA-approved for ankylosing spondylitis (AS) and for psoriatic arthritis (PsA): tofacitinib (Xeljanz or Xeljanz XR) and upadacitinib (Rinvoq). Upadacitinib is also approved for non-radiographic axial spondyloarthritis (nr-axSpA).