Background/Purpose: Abatacept is a selective T cell costimulation modulator indicated for  active Rheumatoid Arthritis (RA). Since August 2013, in Italy, the drug has also been available in a subcutaneous(sc) formulation, consisting in a fixed weekly dose of 125 mg. Aim of our study was to analyze the clinical response and the longterm outcome of a series of patients (pts) with RA previously treated with monthly iv infusion and then converted to the sc formulation based on their subjective preference about the way of administration.

Methods: We have retrospectively included 49 pts with RA, converted to sc Abatacept from October 2013 to April 2014. We divided them into two groups, depending on their need to return to the iv administration for the appearance of a disease flare. The main clinical and serological features of the two groups were compared using the Chi-square, T-test or the Mann-Whitney test.

Results: Fifteen pts (30.6%) returned to the iv administration due to a disease flare (mean DAS28: 4.8 vs 2.1, p:<0.001), after a mean of 15 injections (range 4-48): in these pts it has been observed a significant increase of the CRP values (mean:0.29 vs 0.86 mg/dl, p:0.004) and of the number of painful (mean:0.6 vs 4.9, p:<0.001) and swollen joints (mean 0.5 vs 4.2, p:<0.001).The remaining 34 pts (69.4%) continued with the sc formulation. The compared parameters between the two groups are summarized in Table 1. In pts with arthritis flare, disease activity decreased again (mean DAS28: 4.16 vs 2.43, p:<0.001) after returning to the iv infusion, with a significant decrease in the CRP values (mean 0.9 vs 0.4 mg/dl, p:0.04) and in the number of painful (mean:4.9 vs 1.7, p:0.003) and swollen joints (mean:4.2 vs 1.2, p:0.003).One patient discontinued the sc formulation for the onset of headache and nausea, not reported with the iv administration.Twelve months after the switch we have evaluated the persistence in treatment with Abatacept of the original cohort: 32 of the 34 patients (94%) were still treated with sc Abatacept (one withdrawn for sustained remission and one for repeated infections) while only 10 over the 15 (67%) pts who returned to iv Abatacept were still treated with the drug because 5 of them were swapped to other biologics for reactivation of arthritis (p:0.0368).

Conclusion:  Although the safety profile of the sc Abatacept seems to confirm the data previously obtained with the iv use of the drug, a high rate of our patients complained a reduced efficacy, also confirmed by the subanalysis of the objective components of the DAS28 index (CRP values and joints involvement). We failed to identify clear risk factors that may help toward the selection of pts to which propose the formulation switch, however, if an arthritic flare occurs, the return to the iv administration seems to ensure a good control of the disease again. Nevertheless the switch failure seems to predict a reduced persistence efficacy of abatacept during time.

Tab1.