Safety and Efficacy of Sodium Polystyrene Sulfonate in Hyperkalemia

Inclusion Criteria: * Provision of written informed consent. * Over 18 years of age. * Mean i-STAT potassium values between 5.0 - 6.5 mmol/l inclusive, at screening (Study Day 0). * Previous participation in Clinical ZS-002 or ZS-003 protocol(s). However, subjects cannot be enrolled in this study until at least 30 days have elapsed from their last dose in study ZS-003. * Ability to have repeated blood draws or effective venous catheterization. * Women of childbearing potential must be using two forms of medically acceptable contraception (at least one barrier method) and have a negative pregnancy test at screening. Women who are surgically sterile or those who are post-menopausal for at least 2 years are not considered to be of child-bearing potential. Exclusion Criteria: * Pseudohyperkalemia signs and symptoms, such as excessive fist clenching hemolyzed blood specimen, severe leukocytosis or thrombocytosis. * Subjects treated with lactulose, Xifaxan or other non-absorbed antibiotics for hyperammonemia within the last 7 days. * Subjects treated with resins (such as Sevelamer acetate), calcium acetate, calcium carbonate, or lanthanum carbonate, within the last 7 days. * Subjects treated with Sodium Polystyrene Sulfonate (SPS; e.g. Kayexalate®) or ZS (microporous, fractionated, protonated zirconium silicate) within the last 30 days. * Subjects with a life expectancy of less than 3 months. * Subjects who are HIV positive. * Subjects 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. * Women who are pregnant, lactating, or planning to become pregnant. * Subjects with diabetic ketoacidosis. * Presence of any condition which, in the opinion of the investigator, places the subject 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. * Previous treatment with SPS. * Treatment with a drug or device within the last 30 days that has not received regulatory approval at the time of study entry. * Subjects with cardiac arrhythmias that require immediate treatment. * Subjects on insulin where a stable dose has not yet been established.\* * Subjects on dialysis. \* Subjects on stable insulin or insulin analogues can be enrolled. Subjects who have been on the same insulin dose and regimen for \> 14 days are considered stable. Whenever possible, all blood draws collected prior to meals should be collected prior to insulin/insulin analogue treatment.