Safety & Efficacy of Zirconium Silicate Dosed for 28 Days in Hyperkalemia.

Inclusion Criteria: * Provision of written informed consent. * Over 18 years of age. * Two consecutive i-STAT potassium values, measured 60-minutes apart, both ≥5.1 mmol/l and measured within 1 day of the first ZS dose on AP Study Day 1. * 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 AP Study Day 1. Women who are surgically sterile or those who are post-menopausal for at least 2 years are not considered to be of childbearing potential. Exclusion Criteria: * Pseudohyperkalemia signs and symptoms, such as excessive fist clenching hemolyzed blood specimen, history of severe leukocytosis or thrombocytosis. * Subjects treated with lactulose, Xifaxan or other non-absorbed antibiotics for hyperammonemia within 7 days prior to the first dose of study drug. * Subjects treated with resins (such as sevelamer acetate or sodium polystyrene sulfonate \[SPS; e.g. Kayexalate®\]), calcium acetate, calcium carbonate, or lanthanum carbonate, within 7 days prior to the first dose of study drug. * Subjects with a life expectancy of less than 3 months. * 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. * Randomization into the previous ZS-002 or ZS-003 studies. * 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 dialysis.