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Key messages Considerable proportion of patients with SpA have been immunized to the subcutaneous anti-TNF drug they are using. Concomitant use of MTX protects from immunization, whereas SASP does not. Patients with SpA using subcutaneous anti-TNF drugs can benefit from monitoring of the drug trough levels. Abstract Immunization to biological drugs can lead to decreased efficacy and increased risk of adverse effects. The objective of this cross-sectional study was to assess the extent and significance of immunization to subcutaneous tumor necrosis factor (TNF) inhibitors in axial spondyloarthritis (axSpA) patients in real-life setting. A serum sample was taken 1–2 days before the next drug injection. Drug trough concentrations, anti-drug antibodies (ADAb) and TNF-blocking capacity were measured in 273 patients with axSpA using subcutaneous anti-TNF drugs. The clinical activity of SpA was assessed using the Bath AS Disease Activity Index (BASDAI) and the Maastricht AS Entheses Score (MASES). ADAb were found in 11% of the 273 patients: in 21/99 (21%) of patients who used adalimumab, in 0/83 (0%) of those who used etanercept, in 2/79 (3%) of those who used golimumab and in 6/12 (50%) of those who used certolizumab pegol. Use of methotrexate reduced the risk of formation of ADAb, whereas sulfasalazine did not. Presence of ADAb resulted in decreased drug concentration and reduced TNF-blocking capacity. However, low levels of ADAb had no effect on TNF-blocking capacity and did not correlate with disease activity. The drug trough levels were below the consensus target level in 36% of the patients. High BMI correlated with low drug trough concentration. Patients with low drug trough levels had higher disease activity. The presence of anti-drug antibodies was associated with reduced drug trough levels, and the patients with low drug trough levels had higher disease activity. The drug trough levels were below target level in significant proportion of patients and, thus, measuring the drug concentration and ADAb could help to optimize the treatment in SpA patients.

Identifying prognostic factors for remission in early rheumatoid arthritis (ERA) patients is of key clinical importance. We studied patient-reported outcomes (PROs) as predictors of remission in a clinical trial. We randomized 99 untreated ERA patients to receive remission-targeted treatment with three disease-modifying antirheumatic drugs and prednisolone for 24 months, and infliximab or placebo for the initial 6 months. At baseline, we measured following PROs: eight Short Form 36 questionnaire (SF-36) dimensions, patient's global assessment [PGA, visual analogue scale (VAS)], Health Assessment Questionnaire (HAQ), and pain VAS. We used multivariable-adjusted regression models to identify PROs that independently predicted modified American College of Rheumatology remission at 2 years. Follow-up data at 2 years were available for 93 patients (92%), and 58 patients (62%) were in remission. At baseline, patients who achieved remission had higher radiological score (p = 0.04), lower tender joint count (p = 0.001), lower PGA (p = 0.005) and physician's global assessment (p = 0.019), lower HAQ (p = 0.016), less morning stiffness (p = 0.009), and significantly higher scores in seven out of eight SF-36 dimensions compared with patients who did not. In multivariable models that included all PROs, remission was associated with SF-36 dimensions higher vitality (odds ratio 2.01; 95% confidence interval 1.19-3.39) and better emotional role functioning (odds ratio 1.64; 95% confidence interval 1.01-2.68). PGA, pain VAS, HAQ, and other SF-36 dimensions were not associated with remission. We conclude that self-reported vitality and better emotional role functioning are among the most important PROs for the prediction of remission in ERA.