Retention rates of bDMARDs in non-adjusted data. Table 1 summarizes characteristics of all patients and age groups. Patients aged ≥75 years exhibited higher incidence of advanced-stage RA, higher ABA and GC usage, higher pre-existing lung disease prevalence, lower MTX usage, stronger inflammatory responses (e.g., CRP and ESR), higher RF levels, higher CDAI scores, and higher HAQ-DI scores than patients aged <65 and 65–74 years.
Table 2 presents patient characteristics according to bDMARD usage. Additional file 1: Tables S1-3 present characteristics of each age group according to bDMARD usage. TNFi and TCZ usage decreased with age, whereas ABA usage remained comparable across age groups. TNFi-treated patients exhibited shorter disease duration, higher proportions of patients with Steinbrocker’s stage I and II RA and biologics-naïve patients, higher MTX usage, and lower pre-existing lung disease prevalence than ABA- and TCZ-treated patients. ABA-treated patients showed longer disease duration, higher proportion of patients with Steinbrocker’s stage III and IV RA, and higher pre-existing lung disease prevalence than those treated with other bDMARDs. TCZ-treated exhibited lower MTX usage, higher GC usage, higher CRP and ESR levels, and higher CDAI scores than those treated with other bDMARDs.
Three-year retention rates of bDMARDs in all patients and by age group are shown in Additional file 1: Figure S2 and Fig. 1. No significance test was performed because the data were non-adjusted. The three-year retention rate of bDMARDs was 48.9% in all patients (Additional file 1: Figure S2A), 48.6% in patients aged <65 years, 48.9% in patients aged 65–74 years, and 50.6% in patients aged ≥75 years (Additional file 1: Figure S2B). Three-year retention rates of TNFi, ABA, and TCZ were 42.6%, 55.4%, and 64.8%, respectively, in all patients (Fig. 1A). Three-year retention rates in patients aged <65, 65–74, and ≥75 years were 43.1%, 43.2%, and 39.7%, respectively, for TNFi; 52.5%, 54.0%, and 62.9%, respectively, for ABA; and 67.0%, 63.9%, and 58.1%, respectively, for TCZ (Fig. 1B, 1C, and 1D).
Risk factors for bDMARD discontinuation in non-adjusted data. In all patients, the risk factors for drug discontinuation included age (hazard ratio [HR] = 0.992, 95% confidence interval [CI] = 0.986–0.999), female gender (HR = 0.672, 95% CI = 0.554–0.821), HAQ-DI (HR = 1.135, 95% CI = 1.013–1.272), TNFi versus ABA usage (HR = 1.301, 95% CI = 1.065–1.600), TNFi versus TCZ usage (HR = 1.919, 95% CI = 1.475–2.542), and ABA versus TCZ usage (HR = 1.474, 95% CI = 1.085–2.024) (Additional file 1: Table S4). In patients aged <65 years, the risk factors for drug discontinuation were age (HR = 0.988, 95% CI = 0.978–0.998) and TNFi versus TCZ usage (HR = 1.825, 95% CI = 1.289–2.667) (Additional file 1: Table S5). In patients aged 65–74 years, the risk factors for drug discontinuation included age (HR = 0.927, 95% CI = 0.880–0.978), female gender (HR = 0.524, 95% CI = 0.372–0.752), biologics-naïve patients (HR = 0.653, 95% CI = 0.471–0.914), and TNFi versus TCZ usage (HR = 2.128, 95% CI = 1.316–3.673) (Additional file 1: Table S6). In patients aged ≥75 years, the risk factors for drug discontinuation were female gender (HR = 0.520, 95% CI = 0.340–0.820), MTX usage (HR = 0.435, 95% CI = 0.286–0.668), GC usage (HR = 2.085, 95% CI = 1.363–3.141), TNFi versus ABA usage (HR = 2.036, 95% CI = 1.332–3.155), and TNFi versus TCZ usage (HR = 2.220, 95% CI = 1.137–4.871) (Additional file 1: Table S7). bDMARD usage itself was a common risk factor for discontinuation in all age groups.
Retention rates of bDMARDs in adjusted data. Although non-adjusted data analyses suggested great differences in drug retention rates across bDMARD type, the retention rates were affected by patient selection bias. Thus, patient selection bias was minimized by applying IPTW based on generalized propensity score, and the retention rate of each bDMARD was compared among the age groups (Fig. 2). Differences in baseline characteristics were adjusted by IPTW (Additional file 1: Table S8). In all patients, three-year retention rates of TNFi, ABA, and TCZ were 43%, 51%, and 65%, respectively. The retention rate of TCZ was significantly higher than rates of ABA and TNFi (ABA versus TCZ, p = 0.021; TNFi versus TCZ, p < 0.001; Fig. 2A). In patients aged <65 years, three-year retention rates of TNFi, ABA, and TCZ were 43%, 47%, and 69%, respectively. The retention rate of TCZ was significantly higher than rates of ABA and TNFi (ABA versus TCZ, p = 0.017; TNFi versus TCZ, p = 0.002; Fig. 2B). In patients aged 65–74 years, three-year retention rates of TNFi, ABA, and TCZ were 44%, 53%, and 60%, respectively. The retention rate of TCZ was significantly higher than that for TNFi (p = 0.034; Fig. 2C). In patients aged ≥75 years, three-year retention rates for TNFi, ABA, and TCZ were 38%, 63%, and 58%, respectively. The retention rate of ABA was significantly higher than that of TNFi (p = 0.017; Fig. 2D). No statistical analysis was performed for TCZ usage data because of the small sample size. Overall, retention rates of TCZ were higher in patients aged <65 and 65–74 years, and retention rates of ABA increased with age.
Reasons for bDMARD discontinuation in non-adjusted data. Reasons for the discontinuation of each bDMARD were analyzed by age (Table 3 and Additional file 1: Table S9). In patients aged <65 years, discontinuation because of remission was more frequent following treatment with TNFi (16.9%) and less frequent following treatment with TCZ (3.4%). The prevalence of effect insufficiency was higher following treatment with ABA (22.0%) and comparable between treatments with TNFi (14.5%) and TCZ (15.5%). AE incidence was lower following treatment with ABA (4.9%). Particularly, there was no incidence of skin and subcutaneous tissue disorders. Similarly, in patients aged 65–74 years, discontinuation because of remission was more frequent following treatment with TNFi (10.5%) and the prevalence of effect insufficiency was lower following treatment with TCZ (8.5%). AE incidence was comparable among the three drugs. Likewise, in patients aged ≥75 years, discontinuation because of remission was more frequent following treatment with TNFi (9.9%). The prevalence of effect insufficiency was comparable among the three drugs, and AE incidence was lower following treatment with TCZ (6.9%) and ABA (4.3%). Among AEs, the incidence of infections was lower following treatment with ABA. Overall, the rate of discontinuation because of remission was higher following treatment with TNFi and AE incidence was lower following treatment with ABA in all age groups.
Retention rate of each bDMARD in adjusted data after excluding patients who discontinued treatment because of remission. Among the reasons for bDMARD discontinuation, the rate of discontinuation because of remission was higher following treatment with TNFi in each age group. Thus, patients who discontinued treatment because of remission were excluded from the analysis. The background characteristics of the remaining patients according to age and bDMARD usage are presented in Additional file 1: Tables S10-13. Retention rates were analyzed (Additional file 1: Figure S3) after adjusting for differences in baseline characteristics using IPTW (Additional file 1: Table S14). In all patients, three-year retention rates of TNFi, ABA, and TCZ were 48%, 55%, and 69%, respectively. The retention rate of TCZ was significantly higher than rates of ABA and TNFi (ABA versus TCZ, p = 0.029; TNFi versus TCZ, p = 0.001; Additional file 1: Figure S3A). In patients aged <65 years, three-year retention rates of TNFi, ABA, and TCZ were 52%, 52%, and 73%, respectively. The retention rate of TCZ was significantly higher than rates for ABA and TNFi (ABA versus TCZ, p = 0.025; TNFi versus TCZ, p = 0.011; Additional file 1: Figure S3B). In patients aged 65–74 years, three-year retention rates of TNFi, ABA, and TCZ were 48%, 55%, and 63%, respectively. The retention rate of TCZ was significantly higher than that of TNFi (p = 0.048; Additional file 1: Figure S3C). In patients aged ≥75 years, three-year retention rates of TNFi, ABA, and TCZ were 42%, 65%, and 63%, respectively. The retention rate of ABA was significantly higher than that of TNFi (p = 0.019; Additional file 1: Figure S3D). No statistical analysis was performed for TCZ data because of the small sample size. Overall, similar results to those shown in Fig. 2 were obtained even after patients who discontinued treatment because of remission were excluded.
Changes in disease activity in non-adjusted and adjusted data. Changes in CDAI were analyzed to evaluate the effects of bDMARDs. First, non-adjusted data analysis was performed to analyze CDAI at baseline and 1, 2, and 3 years (Additional file 1: Figure S4). In all patients and in each age group, CDAI tended to change in a similar manner among patients treated with TNFi, ABA, and TCZ (Additional file 1: Figure S4A, B, C, and D). Disease activity remained low in many patients who continued treatment, regardless of the bDMARD type. Furthermore, changes in CDAI from baseline to 1, 2, and 3 years were analyzed using IPTW based on generalized propensity scores (Fig. 3). In all patients, the greatest improvement in CDAI was observed with TNFi treatment, with mean differences of −12.2 (95% CI = −13.5 to −10.9) at 1, −12.3 (95% CI = −14.2 to −10.5) at 2, and −13.6 (95% CI = −15.9 to −11.2) at 3 years (Fig. 3A). Patients aged <65 years showed the greatest improvement in CDAI following TNFi treatment, with a mean difference of −12.9 (95% CI = −14.5 to −11.3) at 1 year (Fig. 3B). Conversely, in the remaining age groups, there were no significant differences in the degree of CDAI improvement following TNFi, ABA, or TCZ treatment (Fig. 3C and D). In patients aged 65–74 and ≥75 years (Fig. 3C and D), differences in CDAI at 1 year were −11.5 (95% CI = −14.0 to −9.0) and −11.6 (95% CI = −15.5 to −7.7), respectively, for TNFi, −4.7 (95% CI: −9.7 to 0.2) and −6.4 (95% CI = −10.9 to −2.0), respectively, for ABA, and −3.1 (95% CI = −8.9 to 2.6) and −3.8 (95% CI = −14.6 to 6.9), respectively, for TCZ. For TCZ, because of the small sample size, the 95% CIs for changes in CDAI at 2 and 3 years were wide, particularly in the older age groups, and the results for this drug should only be used as a reference.