Therapeutic drug monitoring is used to guide anti-tumour necrosis factor [TNF] therapy. However, the associations between serum drug levels [SDL], TNF-bound, and free anti-TNF in the target tissue are incompletely defined. We aimed to assess the interactions between these parameters in inflammatory bowel disease [IBD] patients.
assays [ELISA assays] were used to detect free drug and TNF-drug complexes in intestinal tissues. Concurrent SDL, anti-drug antibodies [ADA], pharmacotherapy, clinical response, endoscopic appearance, and histological severity were determined. Comparisons between anti-TNFs and paired inflamed/non-inflamed tissue were performed. Variables were correlated and potential interactions detected using multivariate analysis.
A total of 95 biopsies taken from 49 anti-TNF treated IBD patients [26 receiving infliximab and 23 adalimumab] were studied. Free drug levels were higher in inflamed compared with non-inflamed paired specimens. Tissue free-drug and TNF-drug complexes levels were higher in adalimumab-treated patients. In adalimumab-treated patients, SDL were correlated with free drug, but not TNF-drug complex levels, in both inflamed and non-inflamed segments. In infliximab-treated patients, higher SDL were associated with the presence of tissue free drug in both inflamed and non-inflamed segments, whereas TNF-drug complexes were mostly detected in non-inflamed but not in inflamed tissue. In the presence of ADA, neither free drug nor TNF-infliximab complexes were measured in the tissue. Tissue levels did not correlate well with clinical, endoscopic, or histological scores.
SDL correlated with tissue free drug levels; however, different dynamics were observed for TNF-drug complex levels. Infliximab and adalimumab tissue drug dynamics differ. Better understanding of these interactions may allow future therapeutic optimisation.