Background Anti-Tumor Necrosis Factor (TNF)alpha drugs play a fundamental role in Ankylosing Spondylitis (AS) therapy. Nevertheless their use is associated to potential side effects, such as a higher frequency of infection, and high healthcare costs. On these bases, a dose reduction strategy (lengthening drug administration interval) is often attempted in clinical practice.

Objectives 1) to retrospectively compare the features of anti-TNFalpha-treated AS patients who could lengthen the administration interval (group A) with those of patients who needed to maintain standard dosage (group B); 2) to evaluate the impact of dose reduction on infection frequency; 3) to evaluate cost-savings in group A.

Methods All AS patients attending the spondyloarthritis outpatients clinic- Rheumatology Unit of University of Padova and of University of Rome “Tor Vergata” between January 2011 to April 2015 who were treated with anti-TNFalpha (infliximab, adalimumab, etanercept) at a standard dose for at least 6 months with a good control of disease activity (ASDAS <2.1) were prescribed a dose reduction regimen. Some patients were able to maintain the new regimen (group A), while others were not because of symptom flare-up (group B). Disease activity (ASDAS, BASDAI), inflammatory (CRP), functional and (BASFI) and metrologic (BASMI) indexes were recorded at baseline (t0), after 6 months (t6), then once a year (t12, t24, t36, t 48) for a 4-year follow-up.

Results Data from 96 AS patients (25 females, 26.04%; mean age 47.62±13.39 years) were examined. Drug administration interval, which could be lengthened in 66 (68.75%) patients (group A) without flare-ups or functional worsening, was associated to an improvement in ASDAS [t0=2.1 (1.49) vs t48=1.00 (0.29); p<0.0001]; BASDAI [t0=39 (49.6) vs t48=9.5 (14); p<0.0001]; BASFI [t0=22 (35) vs t48=1 (11); p<0.0001]. At the end of the observation period (t48), group A showed better physical functioning and lower disease activity compared to group B [BASFI A vs B =1 (36.18) vs 17.5 (7.3), ASDAS 1 (0.3) vs 1.6 (1.15); CRP 2.15 (2.1) vs 3.1 (7.3) mg/L]. At t0 group A had a less severe inflammatory status [CRP A vs B 2.9 (3.3) vs 4.7 (6.4) mg/L; p=0.0134], and a negative family history for spondiloarthritis (p=0.0318), while no significant difference was observed for smoking, psoriasis, peripheral arthritis, dactylitis, uveitis, enthesitis in more than 4 sites and HLA B27. The number of patients who developed infections during the observation period was significantly lower in group A (p=0,007); the average cost saving at t48 for group A vs group B was: 7.060 vs 14.820 € for infliximab; 6357 vs 13.260 € for etanercept; 11840 vs 12.917 € for adalimumab.

Conclusions Lenghtening anti-TNFalpha administration interval appears to be a valid approach in patients with a less severe inflammatory status, and a negative family history of spondyloarthritis. Dose reduction regimen is associated to lower infection frequency and less expense for National Health Care System.

1. Arends S, van der Veer E, Kamps FB, et al. Patient-tailored dose reduction of TNF-α blocking agents in ankylosing spondylitis patients with stable low disease activity in daily clinical practice. Clin Exp Rheumatol. 2015;33:174–80.

Disclosure of Interest None declared