Clinical relevance of detecting anti-infliximab antibodies with a drug-tolerant assay: post hoc analysis of the TAXIT trial

OBJECTIVE: To evaluate the clinical relevance of antidrug antibodies (ADAs) measured using a drug-tolerant assay in a post hoc analysis of the Trough Concentration (TC) Adapted Infliximab Treatment (TAXIT) randomised controlled trial. DESIGN: ADA in serum samples (n=221) of 76 patients enrolled in TAXIT, who presented with an infliximab TC <3 µg/mL at screening, were reanalysed after optimisation and at the end of the study using a drug-tolerant ADA assay. Patients underwent dose escalation to achieve therapeutic TCs between 3 µg/mL and 7 µg/mL prior to randomisation. Patients were grouped into quartiles (Q1-4) according to ADA concentration at screening. RESULTS: Using a drug-tolerant assay, the immunogenicity detection rate increased from 21% (drug-sensitive assay) to 63% at screening, from 0% to 51% after optimisation and from 3% to 42% at the end of TAXIT. Patients in ADA Q4 required a higher cumulative infliximab dose (2390 (880-2998) mg) to achieve target TCs, resulting in a higher drug cost (€10 712 (4120-13 596)) compared with ADA-negative patients (€2060 (1648-3296)) and patients in ADA Q1/Q2 (€2060 (1648-4120)/€2060 (1751-3296), p