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Introduction: The renoprotective effect of renin-angiotensin (RAS) blockers (angiotensin converting enzyme inhibitors and angiotensin receptor blockers) has been questioned in patients with advanced chronic kidney disease (CKD). Moreover, combination therapy (dual RAS blockade) can further accelerate renal function decline in some populations at risk. However, it is unknown whether this adverse outcome is due to a dose-dependent effect or if it can be attributed more specifically to a drug interaction. Aim This study aims to investigate if the rate of renal function decline in advanced CKD patients is associated to the doses of RAS blockers, and if dual RAS blockade worsens renal function independently of major confounding factors., Material and Methods: Retrospective, observational study in an incident cohort of adult patients with CKD stage 4 or 5 not on dialysis, treated with RAS blockers for at least 3 months prior to the study inclusion. Inclusion criteria were: having at least three consecutive measurements of estimated glomerular filtration rate (eGFR) in a follow-up period >3 months. Decline in renal function was estimated as the slope of the individual linear regression line of eGFR over follow-up time. Equipotent doses of RAS blockers were normalised for a body weight of 70kg or a body surface area of 1.73m 2 (END-RASI). Associations of END-RASI or dual RAS blockade with the rate of renal function decline were analysed by uni- or multivariate linear regression models, accounting for major confounding variables., Results: The study group consisted of 813 patients (mean age 64±14 years, 430 males) with a mean eGFR 14.9±4.2ml/min/1.73m 2 ; 729 patients were on RAS blockade monotherapy and 84 on dual RAS blockade. Median END-RASI in the whole group was 0.91 (I.Q. ranges: 0.69-1.20). Patients on dual RAS blockade had significantly higher END-RASI than the rest of study patients (1.52±0.49 vs. 0.93±0.44; p<0.0001). In univariate linear regression, END-RASI were significantly correlated with eGFR decline (R=-0.149; p<0.0001). Patients on dual RAS blockade showed a significantly faster decline of renal function than the rest of the study patients (-6.19±5.57 vs. -3.04±5.37ml/min/1.73m 2 /year, p<0.0001). By multivariate linear regression, while dual RAS blockade remained independent and significantly associated with faster renal function decline (beta=-0.094; p=0.005), END-RASI (normalised either for body weight or surface area) did not reach statistical significance., Conclusion: END-RASI are significantly associated with the rate of renal function decline in advanced CKD patients. However, the detrimental effect of dual RAS blockade on CKD progression seems to be independent of END-RASI and other major confounding factors., (Copyright © 2019 Sociedad Española de Nefrología. Published by Elsevier España, S.L.U. All rights reserved.)