Background The spondyloarthritis (SpA) patients treated under TNF inhibitors (TNFi) with detectable antidrug antibodies (ADA) often develop loss of efficacy. Concomitant therapy with methotrexate (MTX) appears to reduce the the immunogenicity of biological drugs.

Objectives To analyze if the use of combined therapy with MTX and TNFi can reduce the incidence of ADA and whether its effect is MTX dose dependent in SpA patients.

Methods In this retrospective observational study, 162 SpA patients (including ankylosing spondylitis, Psoriatic SpA, SpA associated with inflammatory bowel disease and undifferentiated SpA) were included. The patients are treated with infliximab (Ifx) or adalimumab (Ada). The presence of ADA were measured at baseline and before each administration by ELISA to complete a follow up of 3 years. The patients were divided in two groups [MTX-15 (dose <15 mg/week) and MTX+15 (≥15 mg/week)] to study the influence of baseline MTX dose on immunogenicity. The statistical analysis was performed using SPSS 11.0.

Results Eighty nine out of 162 (54,9%) patients were male. Eighty five out of 162 (52,5%) patients received Ifx and 77 out of 162 (47,5%) Ada. The mean duration of treatment was 13.38±9.19 years to Ifx and 12.71±10.46 years for Ada. Forty five patients received MTX weekly at baseline [25/85 (29.4%)in Ifx and 20/77 (26%)in Ada]. The mean dose of MTX was 15,9±4.76 mg/week. Twenty nine out of 162 (17,9%) patients developed ADA, and ADA presence was significantly higher in SpA patients on Ifx therapy [21/85 (24.7%) in Ifx vs 8/77 (10.4%) in Ada, p=0.018)]. The presence of ADA was less frequent in SpA patients taking MTX [3/162 (1.8%) with MTX vs 26/162 (16%) without MTX, p=0.021]. No statistically differences were observed in the influence of baseline MTX dose on the ADA appearance (in Ifx: 2/18 (11,1%) in MTX+15 vs 1/9 (11,1%)in MTX-15, p=1,0; in Ada: 1/17 (5,9%) in MTX+15 vs 0/4 (0,0%)in MTX-15, p=1,0).

Conclusions In this cohort of SpA patients treated with Ifx and Ada, the use of MTX has a preventive effect on the ADA development. However, the baseline MTX dose is not a determinant factor to get this effect. Further prospective studies are needed to confirm these data.

Disclosure of Interest A. Villalba Yllan: None declared, C. Plasencia Grant/research support: Pfizer, D. Pascual-Salcedo Grant/research support: Pfizer, Speakers bureau: Pfizer, D. Peiteado: None declared, L. Nuño: None declared, G. Bonilla: None declared, R. del Moral: None declared, A. Balsa Grant/research support: Pfizer, Speakers bureau: Pfizer, Roche, Abbvie, E. Martin Mola Speakers bureau: Pfizer, Roche, Abbvie, Amgen

DOI 10.1136/annrheumdis-2014-eular.5819