Background: Infliximab, an anti–tumor necrosis factor monoclonal antibody, has revolutionized the pharmacological management of immune-mediated inflammatory diseases (IMIDs). This position statement critically reviews and examines existing data on therapeutic drug monitoring (TDM) of infliximab in patients with IMIDs. It provides a practical guide on implementing TDM in current clinical practices and outlines priority areas for future research. Methods: The endorsing TDM of Biologics and Pharmacometrics Committees of the International Association of TDM and Clinical Toxicology collaborated to create this position statement. Results: Accumulating data support the evidence for TDM of infliximab in the treatment of inflammatory bowel diseases, with limited investigation in other IMIDs. A universal approach to TDM may not fully realize the benefits of improving therapeutic outcomes. Patients at risk for increased infliximab clearance, particularly with a proactive strategy, stand to gain the most from TDM. Personalized exposure targets based on therapeutic goals, patient phenotype, and infliximab administration route are recommended. Rapid assays and home sampling strategies offer flexibility for point-of-care TDM. Ongoing studies on model-informed precision dosing in inflammatory bowel disease will help assess the additional value of precision dosing software tools. Patient education and empowerment, and electronic health record–integrated TDM solutions will facilitate routine TDM implementation. Although optimization of therapeutic effectiveness is a primary focus, the cost-reducing potential of TDM also merits consideration. Conclusions: Successful implementation of TDM for infliximab necessitates interdisciplinary collaboration among clinicians, hospital pharmacists, and (quantitative) clinical pharmacologists to ensure an efficient research trajectory.

Background Cost‐effective use of biologicals is becoming increasingly important. Monitoring drug concentrations has emerged as a valuable tool to guide clinical decision‐making as drug concentrations have been linked to clinical outcomes. The presence of a concentration‐response relationship for ustekinumab at trough is uncertain due to the contradictory results reported. Objectives To investigate the relationship between 4‐week post injection ustekinumab concentrations and clinical response in psoriasis patients. Methods In this cross‐sectional study, 49 moderate‐to‐severe psoriasis patients treated with 45 or 90 mg ustekinumab every 12 weeks for ≥16 weeks were included. Ustekinumab serum concentrations and anti‐ustekinumab antibodies were measured at week 4 upon injection and disease severity was assessed by Psoriasis Area and Severity Index (PASI). Results At week 4 upon injection, a significant negative correlation was observed between ustekinumab concentrations and absolute PASI score up to 5.9 μg/ml (ρ = ‐0.357, p = 0.032). Ustekinumab concentrations were higher in optimal responders (PASI≤2) compared to suboptimal responders (PASI>2) (4.0 vs 2.8 μg/ml, p = 0.036). The ustekinumab concentration threshold associated with optimal response was determined to be 3.6 μg/ml (area under the curve = 0.71, sensitivity = 86%, specificity = 63%). Only one patient (2%) had anti‐ustekinumab antibodies. Psoriatic arthritis was identified as an independent predictor of higher PASI scores and higher ustekinumab concentrations (p = 0.003 and p = 0.048, respectively). Conclusion A concentration‐response relationship at week 4 upon injection was observed for ustekinumab‐treated psoriasis patients. Monitoring 4‐week post injection ustekinumab concentrations could timely identify underexposed patients who might benefit from treatment optimization.

Therapeutic drug monitoring (TDM) may lead to more rational use of biologics. Still, TDM is largely underexplored in psoriasis. Little is known about the dosing behavior of biologics by dermatologi...