Open-label Safety of Sodium Zirconium Cyclosilicate for up to 12 Months in Japanese Subjects With Hyperkalemia

The Open-Label Maintenance Study contains an Correction Phase, in which subjects will be dosed with ZS 10 g three times daily (tid) for 24 to 72 hours, followed by a 12-month long-term Maintenance Phase.

The study will start with the screening period, and all baseline parameters should be measured/collected up to 1 day prior to administration of first dose of study drug on Correction Phase Day 1. Subjects with 2 consecutive i-STAT potassium values ≥ 5.1 mmol/L will enter the Correction Phase and receive ZS 10 g TID for up to 72 hours, depending on potassium values. Once normokalemia (i-STAT potassium between 3.5 and 5.0 mmol/L, inclusive) is restored (whether after 24, 48 or 72 hours), subjects will be entered into the Maintenance Phase to be dosed with ZS at a starting dose of 5 g QD. Potassium (i-STAT and Central Laboratory) will be measured Days 1, 2, 5, 12, 19 and 26 throughout the first month of study and every 4 weeks thereafter until Day 362 (Visit 23) then patients will be required to complete the EOS visit which is 7±1 days after the last administration of study medication. For patients who do not enter the Maintenance Phase the last visit will be 7±1 day after the last treatment dose in the Correction Phase. The total expected study duration for an individual patient is approximately 53-54 weeks.

Eligibility Criteria:
Inclusion Criteria:

* Provision of informed consent prior to any study specific procedures.
* Patients aged ≥18. For patients aged \<20 years, a written informed consent should be obtained from the patient and his or her legally acceptable representative.
* Two consecutive i-STAT potassium values, measured 60-minutes (± 15 minutes) apart, both ≥ 5.1 mmol/L and measured within 1 day before the first dose of ZS on Correction Phase Study Day 1.
* Patients who are on peritoneal dialysis (PD) can be enrolled if their SK level is ≥5.5 and ≤ 6.5 mmol/L in two consecutive i-STAT potassium evaluation at least 24 hours apart before Day 1 (in each evaluation, two i-STAT potassium measurements at least 1 hour apart are required). i-STAT potassium measurement should be performed in the morning before breakfast and in the evening before dinner in PD patients on continuous ambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis (APD), respectively.
* Women of childbearing potential must be using 2 forms of medically acceptable contraception (at least 1 barrier method) and have a negative pregnancy test within 1 day prior to the first dose of ZS on Correction Phase Study Day 1. Women who are surgically sterile or those who are postmenopausal for at least 1 year are not considered to be of childbearing potential.

Exclusion Criteria:

* Patients treated with lactulose, rifaxan (rifaximin), or other non-absorbed antibiotics for hyperammonemia within 7 days prior to first dose of ZS.
* Patients treated with resins (such as sevelamer hydrochloride, sodium polystyrene sulfonate \[SPS; e.g. Kayexalate®\] or calcium polystyrene sulfonate \[CPS\]), calcium acetate, calcium carbonate, or lanthanum carbonate, within 7 days prior to the first dose of study drug. Washout of SPS and CPS for 7 days (or longer) prior to the first dose of ZS is allowed, if termination of CPS or SPS is judged to be clinically acceptable by the investigator. Documented informed consent has to be obtained prior to the washout.
* Patients with a life expectancy of less than 12 months
* Female patients who are pregnant, lactating, or planning to become pregnant
* Patients who have an active or history of diabetic ketoacidosis
* Known hypersensitivity or previous anaphylaxis to ZS or to components thereof
* Treatment with a drug or device within the last 30 days that has not received regulatory approval at the time of study entry.
* Patients with cardiac arrhythmias that require immediate treatment
* Hemodialysis patients (including those who are on both PD and hemodialysis \[HD\])
* Patients who have been on PD less than 6 months or more than 6 months with a history of hypokalemia within 6 months before Correction Phase Day 1
* Documented Glomerular Filtration Rate (GFR) \< 15 mL/min within 90 days prior to study entry (Non peritoneal dialysis (PD) patients only)
* If patients joined ZS study in the past, the patients cannot join this study within the last 30 days of the last study drug administration day.