The purpose of this study is to evaluate the ability of RDX013 to lower serum potassium in patients with chronic kidney disease with elevated serum potassium levels

Inclusion Criteria:

1. Males or females aged 18 to 85 years, inclusive
2. Serum potassium value 5.1 to <6.5 mmol/L
3. Chronic kidney disease with eGFR ≥20 to <60 mL/min/1.73m2
4. Able to understand and comply with the protocol
5. Willing and able to sign informed consent

Exclusion Criteria:

1. Pseudo-hyperkalemia signs and symptoms
2. Treatment with potassium-lowering drugs within 7 days prior to enrollment/randomization
3. Treatment with glucocorticoids
4. Uncontrolled Type 2 diabetes, defined as most recent historical HbA1c > 10%, or hospitalization to treat hyper- or hypo-glycemia in the past 3 months
5. Diabetic ketoacidosis
6. Severe heart failure, defined as NYHA (New York Heart Association) Class IV or hospitalization to treat heart failure in previous 3 months
7. History of bowel obstruction, severe gastrointestinal disorders, or major gastrointestinal surgery (e.g., large bowel resection)
8. Females who are pregnant, lactating, or not willing to use appropriate contraception

This is a two part study; Part A is open label and Part B is blinded to study participants (all drug labels for treatment arm and placebo will be identical)