Explorative Study to Investigate the Acid-base Response to Sodium and Potassium Salts in Patients With Chronic Kidney Disease.

Rationale: Patients with chronic kidney disease (CKD) consume a low potassium diet which is associated with progressive CKD and cardiovascular disease. Increasing dietary potassium intake to recommended levels may therefore improve cardiorenal outcomes, but the response to increased potassium intake in patients with CKD is unclear. Therefore, the investigators recently tested the response to 40 mmol potassium chloride in patients with CKD and showed that this is generally well-tolerated. However, patients did develop mild hyperchloremic metabolic acidosis, which may offset the beneficial effects of potassium. The investigators hypothesize that this is a form of chloride-induced acidosis that may be prevented by giving potassium with a different anion than chloride. To further investigate this, the investigators propose to test the response to five different sodium and potassium salts in patients with CKD. These results should inform us on how to best correct a potassium-deficient diet in patients with CKD. Objective: To test the effects of five different sodium and potassium salts in patients with CKD. Study design: Investigator-initiated, single-center, placebo-controlled double-blind randomized crossover study. Study population: Adult outpatients (age ≥ 18 years) with CKD stage G3b or G4 using renin-angiotensin-aldosterone system inhibitors (RAAS-I). Intervention: Capsules with 40 mmol potassium chloride, potassium bicarbonate, potassium gluconate, sodium bicarbonate, sodium chloride or placebo (3 x 3 capsules per day). Main study parameters/endpoints: Difference in plasma bicarbonate after treatment. Nature and extent of the burden and risks associated with participation, benefit and group relatedness: The study lasts 6 weeks and consists of 7 visits that will consist of blood sampling, 24-hour urine collection and spot urine collection. We will also provide an automated blood pressure measuring device for at home blood pressure measurements. Although these procedures are time-consuming and may be experienced as burdensome, they are all routine clinical measurements and safe. Patients may experience a pill-burden. The two risks of the salt supplements are hyperkalemia (with potassium salts) and hypertension (with sodium salts). Based on our previous studies a minority of patients is expected to develop these side-effects (\< 12%). Safety measures to prevent, monitor and treat these side-effects are included in the study protocol. There are no direct benefits for patients participating in this trial, but the results will contribute to a better understanding on the feasibility of dietary modifications and salt substitution in patients with CKD to improve health. Patients will be reimbursed for their participation.