Impact of 5-aminosalicylic acid intolerance on progression to difficult-to-treat ulcerative colitis: a retrospective cohort study.

Confirm ulcerative colitis with endoscopy showing continuous colonic inflammation from the rectum plus histology, after excluding infection with two-step CDI testing. Treat mild-moderate disease with 5-ASA by route and extent (suppository for proctitis, enema for left-sided, oral plus rectal for extensive); if 5-ASA fails, treat as moderate-to-severe rather than stepping up gradually. Position advanced therapy by EFFICACY TIER, not by an anti-TNF-first rule. Advanced-therapy-naive, higher efficacy: infliximab, vedolizumab, ozanimod, etrasimod, upadacitinib, risankizumab, guselkumab; intermediate: golimumab, ustekinumab, tofacitinib, filgotinib, mirikizumab; lower: adalimumab. PREVIOUSLY TNF-EXPOSED, higher efficacy: tofacitinib, upadacitinib, ustekinumab; lower: adalimumab, vedolizumab, ozanimod, etrasimod - S1P modulators are weakest in exactly this group. Do not cycle within the anti-TNF class after primary non-response; switch mechanism. Apply treat-to-target (STRIDE-II) to endoscopic improvement (MES 0-1). Screen for acute severe UC by Truelove-Witts and admit for IV steroids. Begin CRC surveillance 8-10 years after DIAGNOSIS for extensive or left-sided disease; isolated proctitis follows average-risk screening.