IFX exposure below 3 μg/mL increases risk of ATIs. Identification of influential pharmacokinetics and ATI factors improves prediction of IFX levels, potentially allowing individualized dosing and cost reduction.

Objective: We investigated relapse rates after anti-tumor necrosis factor (anti-TNF) withdrawal in inflammatory bowel disease (IBD) patients, response to restart of anti-TNF treatment and predictors for relapse. Methods: IBD patients in remission receiving infliximab or adalimumab treatment for !1 year who discontinued treatment were included. Relapse rates and predictors for relapse were studied using survival and Cox regression analysis. Results: In total, 101 patients were included (77 CD, 24 UC). A total of 56 patients (55%) experienced a relapse (CD 38, UC 18) with a median time to relapse of 32 and 18 months in CD and UC, respectively. Of patients that were retreated with the same anti-TNF agent, 84% responded. A trough serum concentration !2 mg/ml within 1 year prior to anti-TNF discontinuation was associated with a higher relapse rate in CD patients (HR 2.89; p ¼ .018), which was more evident in patients requiring retreatment with biologicals, bowel-related surgery or experimental medication (HR: 4.18; p ¼ .009). A young age (<17 years) at diagnosis was associated with a higher relapse rate (HR: 2.29; p ¼ .040) and fecal calprotectin levels <25 mg/g with a lower relapse rate in CD patients (HR: 0.34; p ¼ .041). Relapse rates, requiring treatment with biologicals or experimental medication, was lower in UC patients who continued immunosuppressive treatment (HR: 0.26; p ¼ .042). Conclusions: Approximately 55% of patients relapsed after anti-TNF withdrawal with a median time to relapse of 32 and 18 months in CD and UC, respectively. Retreatment with the same anti-TNF was successful in 84% of patients.

Home-based infliximab infusions were associated with a cost saving of €55 per infusion. Most participants were satisfied and would recommend home-based infusions to others. Infliximab treatment at home might be recommended as routine care for CD patients.