Open-label Safety and Efficacy of Sodium Zirconium Cyclosilicate for up to 12 Months

Subjects with 2 consecutive i STAT potassium values 5.1 mmol/L will enter the Acute Phase and receive ZS 10 g tid for 24 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 enrolled in 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 weekly throughout the first month of study and every 4 weeks thereafter through Month 12. During the Maintenance Phase, the ZS dose may be increased or decreased in increments/decrements of 5 g qd up to a maximum of 15 g qd or a minimum of 5 g every other day based on i STAT potassium measurements as outlined below: • \> 5.0 mmol/L while receiving 5 g qd or 5 g every other day or \> 5.5 mmol/L while receiving 10 g qd: increase ZS dose in 5 g qd increments to a maximum dose of 15 g qd .• Between 3.0 and 3.4 mmol/L, inclusive: decrease ZS dose in 5 g qd decrements to a minimum dose of 5 g every other day; if a subject's i STAT potassium value remains between 3.0 and 3.4 mmol/L, inclusive, on the ZS 5 g every other day dose, the subject will be withdrawn from the study and receive standard of care treatment. There is no limit to the number of dose titrations allowed. Subjects will receive up to 12 months of treatment with open-label ZS.