Infliximab serum concentrations and disease activity in perianal fistulizing Crohn's disease: a cross-sectional study.

Introduction: Several studies associate the presence of higher serum concentrations of infliximab (IFX) with fistula healing in perianal Crohn's disease (CD). This study aimed to evaluate serum IFX concentrations in patients with perianal fistulizing CD (PFCD) in the presence or absence of general, clinical, and radiological activities.

Methods: This was a cross-sectional study in patients with PFCD during maintenance treatment with IFX from two centers. Serum IFX concentrations were measured before their next infusion and anal fistulas were evaluated by clinical examination and magnetic resonance imaging (MRI), whenever possible, performed 90 days before or after serum collection. According to clinical scores, radiological activity, and disease markers, patients were classified as in remission or active disease. Mean serum IFX concentrations were compared between the groups.

Results: Thirty-eight patients with PFCD were included. Demographic characteristics were similar in patients with remission or active disease. The overall mean serum IFX concentration of the entire sample (n = 38) was 5.21 ± 4.75 μg/mL (median 3.63; IQR 1.44-8.82). Serum IFX levels were 6.25 ± 5.34 μg/mL (median 3.62; IQR 1.95-11.03) in the 23 (60.5%) patients in remission and 3.63 ± 3.24 μg/mL (median 3.63; IQR 1.32-6.43; p = 0.226) in the 15 (39 .5%) who presented active disease. When evaluating general, clinical, and radiological activity of PFCD, and deep remission in isolation, no statistical difference between the groups was observed (p = 0.226, p = 0.418, p = 0.126, and p = 0.232, respectively). The 13 (34.2%) patients with an optimized dose of IFX had significantly higher serum concentrations than the remaining 25 (65.8%) with a standard dose: 8.33 ± 4.41 μg/mL (median 8.36; IQR 3.82-11.20) vs. 3.59 ± 4.13 μg/mL (median 1.97; IQR 1.18-3.85) -p = 0.002. Patients in remission and with an optimized IFX dose had significantly higher serum IFX concentrations than those with a standard dose (p = 0.006), whereas no significant difference was observed among those with active disease (p = 0.083).

Conclusion: There were no differences in IFX serum concentrations in patients with clinical or radiological active PFCD as compared with those in remission. Patients with an optimized IFX dose had significantly higher serum concentrations than those with a standard dose. Patients in remission and with an optimized IFX dose had significantly higher serum concentrations than those with a standard dose.