Crohn's disease (CD) is a chronic inflammatory gastrointestinal disease with repeated cycles of exacerbation and remission. Infliximab (IFX), a chimeric anti-TNF-α monoclonal antibody, has been widely used for the treatment of CD. However, no study in Japanese CD patients receiving continuous IFX for more than 1 year has been reported. To avoid therapeutic failure during long-term administration in Japanese CD patients, we evaluated the variable factors of IFX pharmacokinetics and the optimal trough IFX concentration at 8 weeks after administration.
Population pharmacokinetic (PPK) analysis was performed using the nonlinear mixed-effect model based on the IFX serum concentration in 832 samples from 121 patients. A one-compartment model was used to examine interindividual variability in the systemic clearance (CL) of intravenously administered IFX.
PPK estimates (estimated value, RSE%) were total clearance (CL: 0.018 L/h, 9.1) and volumes of distribution (Vd: 7.35 L, 12.0). Interindividual variability for CL and Vd of 0.11 and 0.16, respectively, was found. Body weight, antibody to IFX (ATI), and albumin level were factors affecting the IFX CL. IFX CL was greater in the ATI-positive than in the ATI-negative group. CL was also greater in nonremission patients. There was a significant association between the predicted serum IFX trough concentration at 8 weeks and therapeutic response with long-term continuous administration (p < 0.05), with a higher concentration at 8 weeks seen in the remission group.
Using these variables including body weight, ATI, and albumin level, the IFX dose could be calculated for individual CD patients to achieve the optimal therapeutic range.