Objectives To assess clinical activity, ultrasound synovitis and drug levels in rheumatoid arthritis (RA) patients receiving anti-TNFα therapy with extended interval of administration (EIA).

Methods Prospective observational study. Population: RA patients, in clinical remission, receiving adalimumab (ADL) or etanercept (ETN) with EIA. Clinical activity was assessed by DAS28-ESR, DAS28-CRP, CDAI and SDAI scores at each visit. Twelve-joint ultrasound assessment (elbows, wrists, 2nd and 3rd metacarpophalangeal joints, knees and ankles) was performed evaluating synovitis through B-mode (BM) and Color Doppler signal (CD). A BM and CD score was calculated summing the highest score from each joint to a maximum of 36 points. We consider positive score >1 point. Serum drug levels were measured using Promonitor® ELISA kits (Progenika Biopharma-Grifols, Spain).

Results A total of 39 patients were included since February 2011 to December 2016. One patient was excluded due to blindness violation and 2 patients never reduced anti-TNFα due to low drug levels. 31 patients were women (82%) and the mean age was 61 (39–81) years. Most patients were RF positive (87%) and ACPA positive (74%). 22 patients were with ADL treatment and 16 with ETN. 32 patients (82%) were with DMARD concomitant treatment (18 MTX (46%), 11 LEF (18%), 2 HCQ (5%), 1 SSZ (2%)) and 7 patients were with low-dose CS (18%). Mean time from diagnosis was 14,95 years (range 2,15 – 52,31) and Mean time with current biologic drug was 4,21 years (range 1,39 – 11,07). Nine patients (24%) returned to standard interval due to worsening of clinical activity and one discontinued treatment due to septic arthritis. All of them returned to clinical remission and no anti-drug antibodies were detected. Clinical activity scores, ultrasound scores and drug levels are summarized in table 1.

Conclusions 1. Clinical remission was sustained in most patients receiving ADL or ETN in extended interval of administration (EIA). 2. Drug levels decrease over time. 3. Some patients (24%) returned to standard interval of administration due to clinical worsening. 4. Some patients show subclinical ultrasound synovitis in B-mode (90%) or Color Doppler (50%) 5. It would be advisable to perform periodic ultrasound and monitoring of anti-TNFα levels to maintain clinical remission in patients with EIA.

Acknowledgements This study was supported by a research grant from Fundaciόn Española de Reumatología and AIRE-MB.

Disclosure of Interest J. Senabre Gallego Speakers bureau: MSD, Novartis, Abbvie, UCB, BMS, J. Rosas Gόmez de Salazar: None declared, M. Marco Mingot: None declared, A. Naranjo: None declared, F. Llinares-Tello: None declared, A. Pons: None declared, X. Barber-Vallés: None declared, G. Santos-Soler: None declared, E. Salas-Heredia: None declared, C. Cano: None declared, M. Lorente: None declared, J. A. García Gόmez: None declared, J. Molina: None declared