Real‑world patterns of early 5‑ASA use and time to treatment escalation in Crohn’s disease: a nationwide cohort study using Korean NHIS data

Background Aminosalicylates (mesalazine, sulfasalazine) are used for mild Crohn’s disease, but real‑world comparative data are limited. Aim To compare the time to initiation of corticosteroids or immunosuppressants in Korean patients with Crohn’s disease treated with mesalazine versus sulfasalazine. Methods We conducted a nationwide retrospective cohort study using the Korean National Health Insurance Service database from 2002 to 2022. Adults with Crohn’s disease who received mesalazine or sulfasalazine for more than 30 days were included. The primary outcome was the interval from aminosalicylate initiation to first corticosteroid or immunosuppressant prescription. Demographic and clinical variables were analysed, and multivariable Cox regression identified predictors of treatment escalation. Results Of 18,288 eligible patients, 17,217 (94.1%) received mesalazine and 1,071 (5.9%) received sulfasalazine. Mesalazine prescribing increased from 79.3% in 2002 to 98.9% in 2022, whereas sulfasalazine decreased from 20.7% to 1.1%. Median time to corticosteroid or immunosuppressant initiation was shorter with mesalazine (72.3 days) than with sulfasalazine (100.7 days; P  = 0.0089). Earlier escalation was associated with male sex, younger age, metropolitan residence, and absence of hypertension or cerebrovascular disease. Conclusions In this nationwide cohort, mesalazine was the predominant aminosalicylate and was associated with earlier treatment escalation than sulfasalazine, alongside marked shifts in prescribing patterns over two decades. These findings describe real‑world associations from administrative data and may inform, but cannot determine, comparative effectiveness between aminosalicylate formulations.