AbstractBackground and PurposeMillions of patients with inflammatory diseases are treated with tumour necrosis factor (TNF) inhibitors (TNFi). Individual treatment response varies, in part related to variable drug clearance. The role of TNF–TNFi complexes in clearance of the different TNFi is controversial. Moreover, mechanistic insight into the structural aspects and biological significance of TNF–TNFi complexes is lacking. We hypothesized a role for Fc‐mediated clearance of TNF–TNFi immune complexes. Therefore, we investigated circulating TNF–TNFi complexes upon treatment with certolizumab—lacking Fc tails—in comparison with adalimumab, golimumab, infliximab and etanercept.Experimental ApproachDrug‐tolerant ELISAs were developed and used to quantify TNF during adalimumab, golimumab, etanercept, certolizumab and infliximab treatment in patients with inflammatory arthritis or ulcerative colitis for a maximum follow‐up of 1 year. Effects on in vitro TNF production and Fc‐mediated uptake of TNF–TNFi complexes were investigated for all five TNFi.Key ResultsCirculating TNF concentrations were >20‐fold higher during certolizumab treatment compared with adalimumab, reaching up to 23.1 ng·ml−1. Internalization of TNF–TNFi complexes by macrophages depended on Fc valency, with efficient uptake for the full antibody TNFi (three Fc tails), but little or no uptake for etanercept and certolizumab (one and zero Fc tail, respectively). TNF production was not affected by TNFi. Total TNF load did not affect clearance rate of total TNFi.Conclusions and ImplicationsDifferences in TNFi structure profoundly affect clearance of TNF, while it is unlikely that TNF itself significantly contributes to target‐mediated drug disposition of TNFi.