Drug Levels and Antibodies Against TNF-blockers in Spondyloarthritis and Rheumatoid Arthritis are Associated with the Activity but they do Not Predict it.

Background: Many patients may have resistance to TNF-blockers. These drugs may induce neutralizing antibodies. The determination of the drug levels of TNF-blockers and Anti-Drug Antibodies (ADAs) against TNF-blockers may help to make clinical decisions.