Ann Rheum Dis 2010;69:817–821. doi:10.1136/ard.2009.112847 817

Objective To investigate how antibodies against anti-tumour necrosis factor (anti-TNF) agents infl uence response after switching from infl iximab to adalimumab in rheumatoid arthritis (RA). Methods This cohort study consisted of 235 patients with RA, all treated with adalimumab. At baseline 52 patients (22%) had been previously treated with infl iximab (‘switchers’), and 183 (78%) were anti-TNF naive. Disease activity (using the 28-joint count Disease Activity Score (DAS28)) and presence of antibodies against infl iximab and adalimumab were assessed. Clinical response to adalimumab was compared between switchers and anti-TNF naive patients and their anti-infl iximab and anti-adalimumab antibody status. Results After 28 weeks of adalimumab treatment the decrease in DAS28 (∆DAS28) for the 235 patients was 1.6±1.5 (mean±SD). Anti-adalimumab antibodies were detected in 46 patients (20%). ∆DAS28 was 1.8±1.4 in patients without anti-adalimumab and 0.6±1.3 in patients with anti-adalimumab (p<0.0001). Thirty-three of the 52 switchers (63%) had anti-infl iximab antibodies. Patients with anti-infl iximab more often developed anti-adalimumab than anti-TNF naive patients (11 (33%) vs 32 (18%); p=0.039). ∆DAS28 was greater for anti-TNF naive patients (1.7±1.5) than for switchers without anti-infl iximab antibodies (∆DAS28=0.9±1.4) (p=0.009). ∆DAS28 for switchers with anti-infl iximab was 1.2±1.3 and did not differ signifi cantly from anti-TNF naive patients (p=0.262). Conclusion Switchers with anti-infl iximab antibodies more often develop antibodies against adalimumab than anti-TNF naive patients. Response to adalimumab was limited in switchers without anti-infl iximab antibodies, which raises the question whether a second anti-TNF treatment should be offered to patients with RA for whom an initial treatment with an anti-TNF blocker fails, in the absence of anti-biological antibodies