Supplementary Material for: Finerenone in primary IgA nephropathy: A matched case-control study

Introduction: This study aimed to evaluate whether supplementation of finerenone to renin-angiotensin system inhibitor (RASi) therapy confers additional renoprotective benefit versus RASi therapy only in clinical IgA nephropathy (IgAN). Methods: Primary IgAN patients administered RASi therapy at Ruijin Hospital from January 2023 to December 2023 were retrospectively enrolled, with an eGFR ≥ 25 mL/min/1.73 m2. IgAN patients treated with steroids or immunosuppressants were excluded. The analyzed patients were divided into the finerenone and RASi groups based on finerenone use status. Patients were selected via 1:1 propensity score matching (PSM) based on age, sex, 24-hour urine protein, eGFR, and SGLT2i use status. The primary endpoint was the change in urinary protein at 9 months compared to baseline. Secondary endpoints included eGFR decline and safety outcomes, with additional data collection at 12 months. Results: After PSM, 62 patients were included, with 31 in each group. The finerenone group showed a greater reduction in urinary protein (-29.03% vs. 41.47%, p < 0.001) and a slower least-squares mean eGFR slope (1.25 vs. -3.38 mL/min/1.73 m², p = 0.04) at 9 months compared with the RASi group. Subgroup analysis suggested a trend toward greater improvement with SGLT2i addition, but the interaction was not statistically significant (p = 0.31), likely due to the limited sample size. Extended follow-up at 12 months confirmed these findings, demonstrating a sustained reduction in proteinuria (P = 0.001). Hyperkalemia rates remained similar in both groups at 4, 9, and 12 months. Conclusions: The combination of finerenone with RASi is associated with a greater reduction in urinary protein and potentially better stabilization of eGFR compared with RASi alone in IgAN patients. However, these findings require further validation in prospective studies.