High serum levels of ustekinumab are associated with better clinical outcomes during maintenance treatment for inflammatory bowel disease.

Background: Ustekinumab (UST) is an effective treatment option in Crohn's disease (CD) and ulcerative colitis (UC). However, it still remains unclear if therapeutic drug monitoring could be helpful to guide clinicians.

Objectives: The aim of our study was to analyze the relationship between UST through levels (UST) and clinical outcomes in real-world inflammatory bowel disease (IBD) patients.

Design: We performed a unicentric retrospective study including patients with IBD under UST treatment with at least one level determination.

Methods: The following variables were analyzed at the initiation of UST and at each UST measurement: clinical response and remission using the Harvey-Bradshaw Index (HBI) for CD and the Partial Mayo Score (pMayo) for UC; biochemical response and remission using fecal calprotectin and C-reactive protein, among others. Two periods were considered: P1 (time between induction and the first determination of UST) and P2 (time between UST and the second determination of UST).

Results: We included 125 patients, 117 with CD. In P1, 62.4% of patients were on subcutaneous maintenance, and the median UST was 3.1 μg/mL (1.6-5.3). In 44.8% of CD patients (48/117), clinical remission was achieved, with UST significantly higher than those who did not achieve remission (3.7 μg/mL (2.3-5.4) vs 2.3 μg/mL (1.1-5.2);  = 0.04). In the 46 patients with two determinations, statistically significant differences were found between variables in P2 versus P1: clinical remission (73.9% vs 21.7%;  = 0.001); UST (7.2 μg/mL (4.7-11.7) vs 3.4 μg/mL (1.9-6.4);  < 0.001), HBI (4 (4-4.3) vs 8 (4-9);  < 0.001), pMayo (1 (1-3.3) vs 4.5 (3-5);  = 0.042), and corticosteroid use (26.1% vs 41.3%;  = 0.024). Receiver-Operating-Characteristic (ROC) curves were calculated for clinical remission in P2, with UST cutoff value of 6.34 μg/mL for clinical remission and a high rate of intensified patients (98%).

Conclusion: High serum levels of UST were associated with clinical remission during treatment for IBD under intensification treatment, with a cutoff point of 6.3 μg/mL.