Annual Therapeutic Drug Monitoring in Patients with Inflammatory Bowel Disease During Infliximab Maintenance Therapy: Balancing Efficacy with Risk of Pharmacokinetic Failure

Background and Aims: Recent studies indicate that proactive therapeutic drug monitoring (TDM) can improve clinical outcomes in patients with inflammatory bowel disease (IBD) treated with infliximab. Repetitive infliximab trough level (IFX TL) measurements for proactive TDM may increase patient inconvenience and medical costs. Therefore, we aimed to determine the optimal interval for TDM during infliximab maintenance therapy in patients with IBD. Methods: A prospective cohort study was performed on the patients with IBD who were in clinical remission on infliximab maintenance therapy and had IFX TL ≥ 3 μg/mL after one-time dose optimization. Infliximab TL were measured before each infliximab infusion to identify the pharmacokinetic (PK) relapse (two consecutive IFX TL < 3 μg/mL). Kaplan–Meier method was used to calculate the time to PK relapse. Results: A total of 103 patients were enrolled and followed for a median of 18.5 months. PK relapse occurred in 19 patients (18.5%), with a higher rate of PK relapse in patients with IFX TL 3–5 μg/mL (16/60, 26.7%) compared to those with IFX TL ≥ 5 μg/mL (3/43, 7.0%). Kaplan–Meier survival time to maintain 95%, 90%, 85%, 80%, and 75% therapeutic IFX TL persistence rate without PK relapse was 4.1, 10.3, 13.3, 14.3, and 19.8 months, respectively. Log-rank test showed that therapeutic IFX TL persistence rates were significantly lower in patients with IFX TL 3-5 μg/mL group compared to those with IFX TL ≥ 5 μg/mL group (p = 0.010). Kaplan–Meier retention time to maintain 85% therapeutic IFX TL persistence rate without PK relapse was 10.3 months in IFX TL 3-5 μg/mL group and 20.2 months in IFX TL ≥ 5 μg/mL group, respectively. Conclusions: Proactive TDM measuring with IFX TL annually may be helpful in maintaining therapeutic IFX TL ≥ 3 μg/mL in 85% of patients with IBD and clinical remission on infliximab maintenance therapy.