Tremfya PEN 200 mg Injection Tremfya PEN contains Guselkumab, a human immunoglobulin G1 lambda (IgG1λ) monoclonal antibody that selectively binds to the p19 subunit of interleukin-23 (IL-23) and inhibits its interaction with the IL-23 receptor. IL-23 is a naturally occurring cytokine involved in normal inflammatory and immune responses, playing a central role in driving autoimmune conditions such as psoriasis and inflammatory bowel disease. By blocking IL-23, guselkumab inhibits the release of proinflammatory cytokines and chemokines. It is indicated for the treatment of adult patients with moderate-to-severe plaque psoriasis, active psoriatic arthritis, moderately to severely active Crohn's disease, and moderately to severely active ulcerative colitis.