Potassium Correction for RAAS Optimization in Chronic Kidney Disease

The goal of this placebo-controlled, double-blinded cross-over trial is to test whether patiromer, compared with placebo, better enables up-titration of RAAS-blocker treatment in patients with chronic kidney disease stage 3b/4. The main questions it aims to answer are: * Does patiromer allow uptitration of irbesartan, resulting in a significant reduction in albuminuria and blood pressure? * Does patiromer allow uptitration of irbesartan, resulting in a significant reduction in blood pressure? The trial contains the following interventions: * Participants will be switched from their ACEi/ARB to a standardised dose of irbesartan (150 mg/d). * During two 12-week study periods, participants will receive either patiromer 8.4 g/d or placebo. The order of study periods is randomized. * At the start of each study period irbesartan will be up-titrated to 300 mg/d. * After 1 and 6 weeks, at both periods, plasma potassium will be measured and the irbesartan dose will be reduced to 150 mg/d in case plasma potassium exceeds 5.0 mmol/L. * At 12 weeks from the start of the study period, the endpoints will be assessed. * Between the two study periods, there is a 6-week washout. Irbesartan dose during the wash-out period will be 150mg/d. After washout, participants will switch from the patiromer arm to the placebo arm or vice versa.