A Study to Investigate the Safety and Efficacy of ZS in Patients With Hyperkalemia

Inclusion Criteria: * Provision of informed consent prior to any study specific procedures * Female and male patients aged ≥18 and ≤ 90 years * Two consecutive i-STAT potassium values, measured 60-minutes (± 10 minutes) apart, both ≥ 5.1 mmol/l and measured within 1 day of the first ZS dose on 48-hour open-label initial phase Day 1 * Ability to have repeated blood draws or effective venous catheterization * Female patients must be 1 year post-menopausal, surgically sterile, or using an acceptable method of contraception for the duration of the study and for 3 months after the last dose of ZS/matching placebo to prevent pregnancy. Exclusion Criteria: * Involvement in the planning and/or conduct of the study * Participation in another clinical study with an investigational product during the last 3 months * Pseudohyperkalemia signs and symptoms * Patients treated with lactulose, xifaxan (rifaximin) or other non-absorbed antibiotics for hyperammonemia within 7 days prior to the first dose of study drug * Patients treated with resins,calcium acetate,calcium carbonate, or lanthanum carbonate,within 7 days prior to the first dose of study drug * Patients with a life expectancy of less than 3 months * Patients who are severely physically or mentally incapacitated and who in the opinion of investigator are unable to perform the subjects' tasks associated with the protocol * Female patients who are pregnant, lactating, or planning to become pregnant * Patients with diabetic ketoacidosis * Presence of any condition which, in the opinion of the investigator, places the patient at undue risk or potentially jeopardizes the quality of the data to be generated * Known hypersensitivity or previous anaphylaxis to ZS or to components thereof * Patients with cardiac arrhythmias that require immediate treatment * Patients on dialysis * Patients who are blood donors should not donate blood during the study and for 3 months following their last dose of ZS