Infections in inflammatory bowel disease patients on immunomodulator and biologic therapy are not associated with high serum drug levels

Background: Inflammatory bowel disease (IBD) therapies now utilise higher doses of immunomodulatory and biologic therapies, predisposing patients to an increased risk of infections. Aims: We aimed to determine whether infections were associated with high anti-tumour necrosis factor (TNF) drug levels in IBD and to quantify the risk and consequences of infections. Methods: Two retrospective studies were performed, a descriptive cohort study and a matched case–control study. For the matched case–control study, cases of infection occurring on anti-TNF agents were matched in a 1:2 ratio to controls of anti-TNF treated patients without infections. Results: In the descriptive study, 76 infections occurred in 60 patients, including 49 bacterial, 24 viral, four fungal and four parasitic. Of these, 61 (80.3%) were on biologics, 49 (64.5%) on immunomodulators and 11 (14.5%) on corticosteroids. Thirty-four (44.7%) were on combination therapy, 27 (35.5%) on biologic monotherapy and 15 (19.7%) on immunomodulator monotherapy. Median anti-TNF drug levels in infection cases were 3.9 μg/mL for infliximab and 6.0 μg/mL for adalimumab. In the case–control study, 32 cases of infection in 27 anti-TNF treated patients were matched with 64 anti-TNF treated controls without infections. Among infection cases, 59.5% were on combination therapy versus 40.6% on biologic monotherapy (P = 0.59). Median drug levels for cases and controls respectively were 3.9 μg/mL versus 5.5 μg/mL for infliximab (P = 0.72) and 6.0 μg/mL versus 9.9 μg/mL for adalimumab (P = 0.34). Conclusion: Infections in patients with IBD were common, and the risk was highest with combination therapy. Infections were not associated with high serum anti-TNF levels.