Abstract:Objective To analyze the associations of therapeutic drug monitoring(TDM) after induction therapy and during maintenance period with primary non-response(PNR), secondary lost response(SLR), endoscopic mucosal healing(MH), acute infusion reaction and drug withdrawal in the patients with Crohns disease(CD) treated with infliximab(IFX). Methods Forty-seven moderate-severe CD patients were enrolled for a respective analysis, who were admitted to Nanjing Drum Tower Hospital from June 2018 to September 2022 and were initially treated with biological agents. At the 14th week after induction therapy, the first TDM was performed to detect IFX trough concentration(TC) and anti-tumor necrosis factor drug antibody titers (anti-TNF antibody, ATI). IFX TC≥3μg/mL was defined as up-to-standard, and drug dosing optimization was allowed based on TDM results. In the maintenance treatment, the second TDM was conducted. The differences of PNR, SLR, MH, acute infusion reaction and drug withdrawal between 14-week IFX TC up-to-standard group (n=25) and substandard group (n=22) and among different subgroups of IFX TC during maintenance period were analyzed, and the relationship between different IFX TC and ATI positive rate was analyzed. Results At (32±4) weeks, there was a significant difference in MH rate between 14-week up-to-standard group and substandard group(80.0% vs 31.8%, χ²=11.113, P＜0.01). In the 14-week up-to-standard group, there were significant differences in the incidences of ATI, infusion reaction and drug withdrawal between second up-to-standard subgroup and second substandard subgroup(P<0.01). In 14-week substandard group, there was significant difference in the rate of ATI between the two subgroups (P<0.05). The ATI positive rate of extremely low IFX TC group（＜1.0μg/mL）was 53.9%, which was significantly higher than other groups（P<0.05）. Conclusion IFX TC at 14-week after induction therapy is closely related to the first endoscopic reexamination of MH in CD patients ,and IFX TC during the maintenance period is related to ATI , infusion reaction and drug withdrawal. More economical and convenient proactive TDM strategy is expected to maintain drug efficacy in CD patients.