Ustekinumab trough concentrations predict clinical remission in perianal fistulizing crohn's disease: a real-world retrospective cohort study.

Background: Limited evidence exists on the long-term efficacy of ustekinumab (UST) in perianal fistulizing Crohn's disease (PFCD), and the optimal UST trough level for predicting fistula remission remains uncertain. This study aimed to assess both short- and long-term effectiveness of UST in PFCD and to identify thresholds predicting fistula clinical remission.

Methods: This retrospective cohort included 89 PFCD patients treated with UST. Evaluations utilized the Harvey-Bradshaw Index (HBI), Perianal Crohn's Disease Activity Index (PDAI), and Fistula Drainage Assessment (FDA). Magnetic resonance imaging (MRI) with the Van Assche Index (VAI) was performed at 52 weeks. Receiver operating characteristic (ROC) curves identified UST trough levels predictive of clinical remission.

Results: The fistula clinical remission rates were 66.3% (59/89) at 16/20 weeks and 74.2% (66/89) at 52 weeks. Biochemical markers, including CRP, ESR, and PLT, significantly decreased, while RBC and HB levels increased after treatment (p < 0.05). MRI showed fistula improvement in 54.7% (35/64) of patients and complete healing in 21.8% (14/64). Comparative analysis revealed that anti-TNF-naïve patients had significantly higher rates of fistula remission, whereas seton insertion did not affect long-term fistula healing. ROC analysis identified UST trough concentrations ≥3.95 µg/mL at 16/20 weeks as predictive of clinical fistula remission (AUC: 0.791; sensitivity: 73.8%; specificity: 78.6%).

Conclusion: UST achieves 74.2% fistula clinical remission at 52 weeks in PFCD, with trough concentrations at 16/20 weeks predictive of clinical remission. These findings support the use of therapeutic drug monitoring(TDM) to optimize clinical outcomes.