Pharmacodynamic & Safety of Patiromer in Children & Adolescents (2-<18 Yrs) With Chronic Kidney Disease and Hyperkalemia

Inclusion Criteria: * Written assent (when applicable) and written informed consent by a legally authorized representative provided prior to participation in the study * Age 2 - \<18 years old * CKD defined by the estimated glomerular filtration rate (eGFR) \<90 mL/min/1.73m2, including renal transplant subjects, based on local creatinine measurement at screening * Two potassium measurements of 5.1 to \< 6.5 mEq/L performed on separate days * In the opinion of the study doctor, is expected to require treatment for hyperkalemia for at least 6 month * If taking any renin-angiotensin-aldosterone system inhibitors (RAASi) beta blockers or diuretic medications, must be on a stable dose for at least 28 days prior to Screening * Negative pregnancy test in females of child-bearing potential Exclusion Criteria: * Pseudohyperkalemia due to hemolysis or to abnormally high numbers of platelets (\>500,000/mm3), leukocytes (\>70,000/mm3), or erythrocytes (hematocrit \>55%) at Screening based on results obtained locally * Evidence of potassium-related electrocardiogram (ECG) changes at Screening * Any of the following kidney conditions: maintenance hemodialysis or peritoneal dialysis, renal artery stenosis, and acute kidney injury or a history of acute renal insufficiency in the past 3 months * Severe disorder of stomach or intestines including surgery that could affect gastrointestinal transit of the drug * Increased liver enzymes (ALT, AST \> 3 times upper limit of normal) at Screening * Active cancer, currently on cancer treatment or history of cancer in the past 2 years (except for non-melanoma skin cancer) * Heart or liver transplant, or anticipated need for transplant during the study treatment period including a scheduled kidney transplant recipient. (Note: patients currently on a kidney transplant wait list are not excluded unless there is an identified donor). * Alcohol abuse or substance use disorder within 1 year of Screening * Subjects currently being treated with or having taken any one of the following medications (includes resins) in the 7 days prior to Screening: sodium or calcium polystyrene sulfonate, drospirenone * Use of certain medications that can affect blood potassium levels if doses have not been stable for at least 14 days prior to Screening or if doses are anticipated to change during the 14-day PD / Dose Finding Phase * Use of investigational product within 30 days of screening or within 5 half-lives, whichever is longer * Known hypersensitivity to patiromer or its components * In the opinion of the Investigator, any medical condition, uncontrolled systemic disease, or serious intercurrent illness that would significantly decrease study compliance or jeopardize the safety of the subject or potentially affect the quality of the data