Background: Several studies have reported a strong correlation between infliximab (IFX) trough levels (trough levels of infliximab [TLI]) and clinical remission (CR). We aimed to determine threshold values of TLI associated with the occurrence of CR, with or without normal inflammatory biomarkers, including serum C-reactive protein (CRP) and fecal calprotectin (fCal).
Methods: We included prospectively all consecutive patients with inflammatory bowel disease under IFX therapy (5 mg/kg every 8 wk) for at least 6 months. Disease activity (using the Crohn's Disease Activity Index or Mayo score) was recorded, and TLI, CRP, and fCal were measured before IFX infusion.
Results: Two hundred thirteen patients (131 Crohn's disease) were included. The median TLIs were higher in patients who achieved CR compared with those in patients who did not (2.6 versus 1.2 μg/mL, P < 0.01). The median TLI were higher in patients achieving CR with CRP normalization or CR with fCal <250 μg/g in comparison with patients with persistent elevated CRP or fCal (3.5 versus 1.6 μg/mL, P < 0.01 and 4.9 versus 1.8 μg/mL, P < 0.001, respectively). Finally, the median TLIs were higher in patients achieving CR with normal CRP and fCal <50 μg/g in comparison with patients without strictly normal biomarkers (5.9 versus 2.1 μg/mL, P < 0.001). The more the expected level of response to IFX was stringent, the more the median TLI and optimal thresholds were high.
Conclusions: Threshold values of TLI differ according to therapeutic outcomes expected in patients with inflammatory bowel disease under maintenance therapy with IFX.