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

Abstract Introduction: there are several studies in the literature that 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 and deep remission. Methods: a cross-sectional study in patients with PFCD during maintenance treatment with IFX from two centers. Serum IFX concentrations were measured before its next infusion and anal fistulas were evaluated by clinical examination and magnetic resonance imaging (MRI) performed 90 days before or after serum collection. According to clinical scores and endoscopic, radiological, laboratory, and MRI markers, patients were classified as in remission or active disease. Results: 38 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 ug/mL (Median 3.63; IQR 1.44 - 8.82). In the 23 (60.5%) patients in remission, serum IFX levels were 6.25 ± 5.34 ug/mL (Median 3.62; IQR 1.95 - 11.03), and in the 15 (39 .5%) who presented active disease of 3.63 ± 3.24 ug/mL (Median 3.63; IQR 1.32 - 6.43; p=0.026). 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 ug/mL (Median 8.36; IQR 3.82 – 11.20) vs. 3.59 ± 4.13 ug/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 concentrations of IFX than those with a standard dose (p=0.006), whereas, among those with active disease, no significant difference was observed (p=0.083). Conclusion: there were no differences in IFX serum concentrations in patients with general, clinical, or radiological active disease 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.