Abstract Background Ustekinumab (UST) targets the IL12/23 p40 subunit, and it is a valuable second-line therapeutic alternative in Crohn’s disease (CD) and ulcerative colitis (UC). The variability in treatment response underscores the need for early identification of predictors of remission, such as UST exposure. To describe UST trough concentrations in a realworld IBD cohort including those with fistulizing CD phenotype, and examine associations of post-induction trough levels with clinical remission at week 26. Methods Retrospective study from a tertiary IBD center. Serum UST troughs were measured after IV induction (260, 390 or 520 mg) and during SC maintenance (90 mg every 8 or 12 weeks). Demographic, clinical and treatment data were collected. Descriptive, t-test/Mann–Whitney U test and logistic regression analysis were utilized. Results Fiftyfive patients received UST, while TDM data were available for 40 out of which 95% diagnosed with CD. Twelve CD patients (32%) had fistulizing disease. All, except one patient, were previously treated with another biologic, mainly anti-TNF (86.84%). In total, 22 post-induction and 30 UST levels during maintenance were available. Postinduction UST levels were significantly higher than those observed during maintenance (7.62 vs. 1.86 μg/mL, p 0.001). Patients with fistulas showed a tendency toward lower levels. Clinical remission at week 26 was associated with higher postinduction UST levels (median 8.12 vs 4.62 μg/mL, p = 0.047). A higher UST trough concentration tended to be associated with greater likelihood of remission (OR = 2.41, 95% CI 0.13–2.22, p = 0.076). Conclusion In this first Serbian realworld series, higher UST levels early after induction showed a positive trend with clinical remission at week 26. Fistulizing CD showed a tendency toward lower concentrations. Although these results are based on small cohort of patients, they support early UST TDM in dose optimization. Conflict of interest: Dr. Kralj, Djordje: No conflict of interest Paravina, Nikola: No conflict of interest Markovic, Srdjan: No conflict of interest Knezevic, Tamara: No conflict of interest Jovanovic, Marija: No conflict of interest Sreckovic, Slobodan: No conflict of interest Kalaba, Ana: No conflict of interest Vucicevic, Katarina: No conflict of interest
Kralj et al. (Thu,) studied this question.