Early Monitoring of Ustekinumab Concentration after Induction is Related to Clinical Remission in Ulcerative Colitis & Crohn`s Disease - STOCUSTE Study

Background Ustekinumab (UST), an anti-interleukin-12/23 antibody, is used to treat moderate to severe inflammatory bowel disease (IBD). The STOCUSTE study includes IBD patients treated with UST at four teaching hospitals in Stockholm to provide long-term follow-up data. We investigated in a real-world setting the utility of therapeutic drug monitoring (TDM) to optimize treatment and correlated the serum concentrationof UST to clinical outcomes. Methods This retrospective study includes patients diagnosed with Crohn’s disease (CD) and ulcerative colitis (UC) treated with UST and followed until withdrawal of treatment for any reason, or until end of study,July 31, 2021. Concentration data and dosing interval were collected at each follow-up (3, 6, 9, 12, 24,36, 48, 60 months) in relation to presence of remission defined as Physician Global Assessment (PGA)= 0. Results In total, 418 patients were included, 322 (48% females) with CD and 96 (46% females) with UC. In 229 patients the UST concentration was analyzed at least once and never in the remaining 188 patients. In general, the UST serum concentrations were above 1 μg/ml. At 3 months follow-up, patients in remission had a significant higher concentration of UST compared to non-remitting patients. (Table 1) in the total cohort, as well as when analyzed separately in UC ad CD. There was no significant difference in UST concentrations at 6 months or later between patients in remission versus non-remission for either IBD diagnosis. Further, TDM was related to higher rates of remission at 3 months of follow-up. Conclusion In this study, early measurement of serum UST (≤3 months) correlated to the clinical response. Serum concentrations at later time points were similar in patients in remission and in patients with active disease. These results from a real-world setting might partly be explained by that serum concentrations were not taken in a systematic manner.