Treatment for inflammatory bowel disease (IBD) is rapidly moving beyond simple symptom management toward the structural restoration of the intestinal mucosa and tissue. Instead of stopping at the alleviation of chronic diarrhea, abdominal pain, and bloody stool, gastroenterologists are increasingly targeting the complete resolution of underlying inflammation visible via endoscopy. Achieving this visual and cellular healing significantly reduces the long-term risk of disease relapse and complications. Against this clinical backdrop, the recent expansion of South Korea’s national health insurance coverage to include a selective interleukin (IL)-23 inhibitor has emerged as a major milestone for patients navigating moderate-to-severe Crohn’s disease and ulcerative colitis.
To mark this regulatory shift, Janssen Korea held a press briefing detailing the national health insurance reimbursement of Tremfya (generic name guselkumab) and exploring its projected impact on the domestic treatment landscape. Effective June 1, 2026, the reimbursement applies to patients presenting with moderately to severely active forms of both primary types of IBD who have demonstrated an inadequate response to traditional therapeutic pathways.
Inflammatory bowel disease is characterized by chronic, relapsing inflammation that compromises the gastrointestinal tract. Its two main manifestations, ulcerative colitis and Crohn’s disease, present distinct clinical challenges. Ulcerative colitis primarily targets the mucosa of the large intestine, yielding debilitating symptoms such as bloody stools, persistent diarrhea, and severe abdominal cramping. Crohn’s disease exhibits a more expansive pathology, capable of generating patchy inflammation anywhere from the mouth to the anus, frequently culminating in structural complications like intestinal strictures, obstructions, or fistulas. Because both conditions cycle unpredictably between flare-ups and temporary improvements, they necessitate rigorous, lifelong management that weighs heavily on a patient's quality of life.
Tremfya addresses this underlying pathology by selectively inhibiting interleukin-23, a key cytokine that propagates inflammatory signaling cascades between immune cells. When IL-23 signaling becomes hyperactivated, it drives the chronic, unyielding inflammation characteristic of the intestinal mucosa in IBD patients. As a fully human monoclonal antibody, Tremfya binds specifically to the p19 subunit of the IL-23 cytokine, effectively blocking these destructive inflammatory pathways at their source.
Under the new insurance guidelines, Tremfya is positioned as a viable biologic alternative for moderate-to-severe patients who cannot tolerate or fail to respond adequately to conventional therapies. For ulcerative colitis, eligibility is extended to patients with inadequate responses to standard first-line options, including corticosteroids, 6-mercaptopurine, and azathioprine. For Crohn's disease, coverage applies to moderately to severely active patients who fail to respond to or tolerate two or more conventional treatments, such as corticosteroids or immunosuppressants, provided they meet a baseline Crohn’s Disease Activity Index (CDAI) threshold of 220 or higher.
Shifting the Therapeutic Paradigm Toward Mucosal and Histologic Healing
The evolving philosophy of IBD care centers on the concept of "deep remission." While historical treatment models focused almost exclusively on clinical remission—the stabilization of visible symptoms like diarrhea and pain—modern gastroenterology recognizes that internal inflammation can quietly persist even when a patient feels perfectly well. This lingering, subclinical inflammation leaves individuals highly vulnerable to sudden relapses and structural bowel damage over time. Consequently, contemporary treatment goals have expanded to mandate deep remission, a state defined by simultaneous clinical improvement, endoscopic mucosal healing, and microscopic (histologic) tissue clearance.
During the press briefing, key insights were shared by Jung Seong-ae, a gastroenterology professor at Ewha Womans University Seoul Hospital and president of the Korean Association for the Study of Intestinal Diseases, alongside Hong Seong-no, a gastroenterology professor at Samsung Medical Center and chair of the association’s IBD Research Group.
Professor Jung Seong-ae emphasized that the expanding treatment goals are essential for true long-term disease modification. She noted that while an array of advanced therapies has entered the market over the last decade, a substantial subset of patients still struggles to achieve stable disease control, underscoring the urgent clinical need for targeted options boasting novel mechanisms of action. Supporting this view, Professor Hong Seong-no explained that Tremfya has demonstrated robust, multi-dimensional efficacy across Crohn’s disease and ulcerative colitis trials, successfully driving clinical, endoscopic, and histologic remission. He noted that real-world treatment selections must carefully weigh distinct patient variables, including disease localization, structural severity, prior biologic exposure, comorbidities, patient preference regarding routes of administration, and overarching safety profiles.
The foundational evidence validating Tremfya's efficacy in Crohn's disease stems from the global Phase 3 GALAXI 2 and 3 clinical trials. In a pooled analysis of these studies, Tremfya demonstrated superior performance when measured against Stelara (generic name ustekinumab) across rigorous endoscopy-based endpoints, including overall endoscopic response, endoscopic remission, and deep remission.
By week 48 of the trials, the endoscopic response rate reached 53 percent in the cohort receiving Tremfya 200 mg every four weeks and 48 percent in the group receiving 100 mg every eight weeks, notably outperforming the 37 percent response rate observed in the Stelara reference group. Furthermore, the rate of deep remission—requiring patients to concurrently hit both clinical and endoscopic remission benchmarks—was logged at 34 percent for the four-week Tremfya regimen and 30 percent for the eight-week regimen, compared to 22 percent in the Stelara arm.
For ulcerative colitis, the therapy’s approval and subsequent reimbursement rest on data from the Phase 3 QUASAR study. At the week 12 induction benchmark, the clinical remission rate for the Tremfya cohort stood at 23 percent, compared to just 8 percent for the placebo group. Moving into the maintenance phase at week 44, approximately 50 percent of patients in the 200 mg every-four-weeks group and 45 percent in the 100 mg every-eight-weeks group maintained stable clinical remission.
Crucially, parallel improvements were observed at the structural and microscopic levels. At week 44, endoscopic remission rates reached 34 percent and 35 percent across the respective Tremfya dosing arms, while histologic remission rates reached 61 percent and 59 percent. Histologic remission denotes a profound state of cellular healing where active inflammation is virtually absent when mucosal tissue biopsies are evaluated under a microscope.
Long-term sustainability data further reinforced these clinical outcomes. Within the QUASAR long-term extension study tracking ulcerative colitis patients, the vast majority of initial responders successfully maintained their therapeutic regimens through week 92. At this extended benchmark, clinical remission rates remained exceptionally high at 74 percent for the four-week dosing schedule and 71 percent for the eight-week schedule. Endoscopic remission rates were sustained at 44 percent and 42 percent, respectively, while histologic remission persisted in 66 percent and 67 percent of patients. Regarding long-term safety, data from the five-year GALAXI-1 extension study for Crohn's disease confirmed a safety profile entirely consistent with Tremfya's previously established indications in other chronic inflammatory conditions, with no new safety signals detected.
Ultimately, the expansion of national health insurance coverage represents a paradigm shift that extends far beyond the introduction of a single drug option. Because IBD is a lifelong condition where initial treatments can lose efficacy over time due to secondary drug resistance, earlier access to diverse biologics with unique mechanics is vital. While these targeted therapies require careful medical oversight, including pre-treatment screening for infection risks, this expanded reimbursement framework equips specialists with the tools needed to intervene aggressively, aiming for total tissue healing from the very beginning.
