Ustekinumab Drug Levels and Outcomes in Inflammatory Bowel Disease.

Background: Data regarding the utility of therapeutic drug monitoring with ustekinumab (UST) are sparse. Our aim was to determine the correlation of UST levels with outcomes in a cohort of patients with inflammatory bowel disease (IBD).

Methods: This was a multicenter, retrospective study of all patients with IBD who received UST from January 1, 2014 to March 1, 2022. The primary outcomes were the correlation of UST level with clinical remission (per physician global assessment), endoscopic healing [the absence of ulcers/erosions in Crohn's disease (CD) and Mayo endoscopic score ≤1 for ulcerative colitis (UC)], and normal serum C-reactive protein (CRP) (≤5 mg/L). Secondary outcomes included defining optimal UST trough levels associated with favorable outcomes.

Results: A total of 71 patients (74.6% with CD; 57.7% female) were included. The median age was 39.5 years [interquartile range (IQR): 26 to 52] and 12.6% were on combination therapy with immunomodulators. Median UST trough levels were significantly higher in patients who achieved endoscopic healing at 5.4 µg/mL versus 3.5 µg/mL ( P =0.035) and normal CRP at 5.5 µg/mL versus. 3.1 µg/mL ( P =0.002). A cutoff UST level of 4.8 µg/mL yielded the highest area under the curve (AUC) of 0.73 (95% CI: 0.61-0.80) to predict a normal CRP followed by a cutoff of 3.5 µg/mL which yielded an AUC of 0.66 (95% CI: 0.52-0.81) to predict endoscopic healing.

Conclusions: UST trough levels were significantly higher in patients who achieved a normal CRP and endoscopic healing. A cutoff UST level of 4.8 µg/mL reliably predicted CRP normalization.