Effect of Renin-Angiotensin System Inhibition on Residual Kidney Function in Peritoneal Dialysis

<i>Background and Objectives</i>: Renin-angiotensin system inhibitors (RASIs) are recommended to preserve residual kidney function (RKF) in patients on peritoneal dialysis (PD); however, evidence of benefit is inconsistent. This study evaluated the effect of RASI on RKF decline among patients undergoing PD. <i>Materials and Methods</i>: We conducted a retrospective cohort study among PD patients at a large metropolitan dialysis centre in Australia. RKF was assessed using residual Kt/V and urine volume from PD adequacy tests. Time zero was PD initiation. RASI exposure was modelled as a time-dependent variable to avoid immortal-time bias. Linear mixed-effects models were fitted for each outcome, including random intercepts and slopes for time (years since PD start) with unstructured covariance. Fixed effects included time, RASI(t), time × RASI(t), age, sex, baseline RKF, PD modality, PD infection episodes, loop diuretic use, and comorbidities. <i>Results</i>: Of 307 PD patients, 231 met the inclusion criteria; 111 (48.1%) received RASI. RASI users were younger than non-users [65 years (IQR 56-74) vs. 72 years (IQR 61-77); <i>p</i> = 0.014]. Residual Kt/V declined by 0.26 units/year; RASI exposure showed no significant effect on urine volume trajectory and a borderline slower Kt/V decline (interaction β = +0.038, <i>p</i> = 0.069). Hospitalisation and PD-related infection rates were similar between groups. <i>Conclusions</i>: RASI therapy was not associated with meaningful RKF preservation in PD patients in this cohort. While earlier studies suggested renoprotective effects of RASI while on PD, our findings align with recent evidence of mixed efficacy. Larger prospective trials are needed to clarify the role of RASI in maintaining RKF and improving long-term outcomes in PD.