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Ustekinumab concentrations shortly after escalation to monthly dosing may identify endoscopic remission in refractory Crohn's disease.

OBJECTIVES
Some patients with Crohn's disease do not achieve remission with the approved maintenance dosing of ustekinumab every 8 weeks, possibly due to insufficient drug exposure. We aimed to study the exposure-response relationship for endoscopic remission and biomarker normalization with ustekinumab dose escalation to every 4 weeks.


METHODS
Out of 135 consecutive patients, 44 with active Crohn's disease despite standard maintenance dosing [at least one of C-reactive protein (CRP) >5 mg/L, fecal calprotectin >100 mg/kg, simple endoscopic score (SES) for Crohn's disease >3] underwent dose escalation to every 4 weeks. Subsequent endoscopic remission (SES-CD ≤3 without ulceration) and biomarker normalization were compared against ustekinumab concentrations.


RESULTS
Dose escalation led to endoscopic remission in 28.6% (8/28), CRP normalization 29.2% (7/24) and fecal calprotectin normalization 51.7% (15/29) of patients. Ustekinumab concentrations after escalation were higher in patients with endoscopic remission (6.90 vs. 4.29 mg/L; P = 0.025) and fecal calprotectin normalization (6.65 vs. 3.74 mg/L; P = 0.001). A threshold of 6.00 mg/L identified endoscopic remission [area under the receiver operating curve (AUROC): 0.775; 95% confidence interval (CI), 0.551-0.999), a threshold of 4.40 mg/L (AUROC 0.755; 95% CI, 0.545-0.964) two months after escalation identified patients with fecal calprotectin normalization at the end of follow-up. Concentrations <3.5 mg/L after escalation precluded endoscopic remission or biomarker normalization.


CONCLUSION
Endoscopic remission was associated with higher ustekinumab concentrations after dose escalation. Patients with concentrations <3.5 mg/L after dose escalation are unlikely to achieve endoscopic remission or biomarker normalization.