⁃ The following inclusion criteria must be met for each participant:

• Paediatric participants (\<12 years of age) with hyperkalaemia at screening.

• Participant's age should not reach 12 years during the 28 days of the pharmacodynamic/dose-ranging period.

• Participant is able to receive regular external feeding and medication, including via tubes, i.e., percutaneous endoscopic gastrostomy (PEG) or entero-gastric feeding tube.

• At screening/baseline, the results from 2 separate and consecutive potassium assessments using the same measurement method (whole blood, plasma, or serum) need to be above the age-appropriate upper limit of normal (ULN).

• If taking any renin-angiotensin aldosterone system inhibitors (RAASi), beta blockers, fludrocortisone, or diuretic medications, must be on a stable dose for at least 14 days prior to screening.

• Parent(s) or legally authorised representative(s) or another appropriate person delegated by the legally authorised representatives must be available to help the study-site personnel ensure follow-up; accompany the participant to the study site on each assessment day; accurately and reliably dispense investigational product as directed.

• Females of childbearing potential must be non-lactating, must have a negative pregnancy test at screening, and must have used an effective, acceptable form of contraception (e.g., abstinence) for at least 1 month before patiromer administration. Females of childbearing potential must agree to continue using contraception throughout the study and for 1 month after the last dose of patiromer.

• If undergoing peritoneal dialysis, participants must be on a stable treatment plan for a minimum of 4 weeks prior to screening, or at least 8 weeks prior to screening if newly initiated on peritoneal dialysis.