Background The approved dose of RTX in RA is 1000mg x2, but some data have suggested similar clinical efficacy with 500mg x2.
Objectives The purpose of this analysis was to compare the efficacy of the two dosages given as first or second treatment course.
Methods Ten European registries submitted anonymized datasets with demographic, efficacy and treatment data for patients who had started RTX. Efficacy of treatment and retreatment was assessed based on DAS28 reductions and EULAR responses after 6 months.
Results Data on RTX dose were available for 2873 out of 3266 patients in CERERRA. 2625 (91.4%) and 248 (8.6%) patients received 1000mg x2 and 500mg x2, respectively. Patients who were treated with 500 mg x2 were significantly older (mean±SD: 55.2±15.8 vs. 52.6±12.6, yrs, p=0.002), had longer disease duration (13.6±11.9 vs. 10.9±8.2, yrs, p<0.0001), higher number of prior DMARDs (2.6±1.3 vs. 2.4±1.4, p=0.04) but lower number of prior biologics (0.7±0.9 vs. 1.0±1.0, p<0.0001) and lower baseline DAS28 (5.7±1.3 vs. 5.9±1.3, p=0.02) than those treated with 1000 mg x2. Additionally they were less likely to receive concomitant DMARDs (72.6% vs. 83.1%, p<0.0001) but more likely to receive concomitant corticosteroids (65.7% vs. 59.3%, p=0.03).
Both dosages lead to significant clinical outcomes at 6 months. Patients with the higher dose (1000mg x2) achieved numerically slightly greater DAS28 reductions at 6 months compared to those treated with the lower dose (500mg x2) (mean DeltaDAS28±SD =1.8±1.3 vs. 1.5±1.5, p=0.3 corrected for baseline DAS28 0.07). Similar percentages of patients achieved EULAR good response (45.3% vs. 48%, p=0.3) and remission (9.4% vs. 13.9%, p=0.2) in the 1000 mg x2 and 500 mg x2 groups, respectively.
At 6±1.5 months 579 patients received retreatment with 1000 x2 mg RTX and 26 patients with 500 mg x2. Patients who received different dose at retreatment that at first treatment, as well as patients who were retreated at different time points during the first year, were disregarded from the analysis. Retreatment with 1000 mg x2 led to even greater DAS28 reductions at 12 than at 6 months (DeltaDAS28 6m =1.94±1.06, DeltaDAS28 12m =2.84±1.46, p by paired t-test <0.0001), while retreatment with 500 mg x2 led to no significant further DAS28 reduction (6m =1.15±1.58, 12m =0.87±1.63, p=0.5). A significantly higher good responders rate was observed for the higher dose of RTX for the retreated patients (82% vs. 16.7%, p=0.001).
Conclusions In this large observational cohort initial treatment with RTX at 500 mg x2 and 1000 mg x2, led to comparable clinical outcomes. The higher dose but not the lower dose was associated with further DAS28 reductions when given as a second treatment course.
Disclosure of Interest None Declared