An oral JAK inhibitor for rheumatoid arthritis and ulcerative colitis.
XELJANZ (tablets and oral solution) and XELJANZ XR (extended-release tablets) are Janus kinase (JAK) inhibitors. XELJANZ tablets and XELJANZ XR are indicated for the treatment of adult patients with: • Moderately to severely active rheumatoid arthritis (RA), who have had an inadequate response or intolerance to one or more TNF blockers. • Active psoriatic arthritis (PsA), who have had an inadequate response or intolerance to one or more TNF blockers. • Active ankylosing spondylitis (AS), who have had an inadequate response or intolerance to one or more TNF blockers. • Moderately to severely active ulcerative colitis (UC), who have had an inadequate response or intolerance to one or more TNF blockers. XELJANZ (tablets and oral solution) are indicated for the treatment of pediatric patients 2 years of age and older with: • Active PsA, who have had an inadequate response or intolerance to …
12.1 Mechanism of Action Tofacitinib is a Janus kinase (JAK) inhibitor. JAKs are intracellular enzymes which transmit signals arising from cytokine or growth factor-receptor interactions on the cellular membrane to influence cellular processes of hematopoiesis and immune cell function. Within the signaling pathway, JAKs phosphorylate and activate Signal Transducers and Activators of Transcription (STATs) which modulate intracellular activity including gene expression. Tofacitinib modulates the signaling pathway at the point of JAKs, preventing the phosphorylation and activation of STATs. JAK enzymes transmit cytokine signaling through pairing of JAKs (e.g., JAK1/JAK3, JAK1/JAK2, JAK1/TyK2, …
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Plain-English summaries and drug-class explainers are written and reviewed by the Priya Life Science editorial team, led by Sreepriya Prasannan (MSc Digital Transformation of Life Sciences (Innopharma Education / Griffith College); MSc & BSc Botany). Data is retrieved automatically from the sources above and cross-checked with AI-assisted verification (Anthropic's Claude) — brand and generic names are matched against the exact FDA product record so that a combination product or a different formulation cannot be mistaken for the drug on this page. An editor reviews the result before publication. We describe this in full in our editorial standards and corrections policy. The FDA data on this page was last retrieved on 7 Aug 2026.