A Study Evaluating the Onset-of-Action, Safety, and Efficacy of RDX227675 for the Treatment of Hyperkalemia

The study consists of a screening visit, a 7-day treatment period, and a 7-day
treatment-free follow-up period.

Inclusion Criteria:

- 18 to 85 years old, inclusive

- Two consecutive i-STAT K values ≥ 5.5 to < 6.5 mmol/L, measured a minimum of
60-minutes apart within 1 day of first RDX227675 dose on Day 1 (prior to
randomization)

- i-STAT K value ≥ 5.5 to < 6.5 mmol/L on Day 1 (prior to randomization)

- Ability to have repeated blood draws or effective venous catheterization

- Females of child bearing potential must have negative urine pregnancy test on Day 1
(prior to randomization)

- Females but be non-pregnant, non-lactating, and either be post-menopausal for at
least 12 months, have documentation of irreversible surgical sterilization, or
confirm the use of one of the acceptable contraceptive methods

- Males must agree to use an appropriate method of contraception or have documented
surgical sterilization

Exclusion Criteria:

- Pseudohyperkalemia signs and symptoms

- Treatment with K lowering drugs, within 7 days prior to randomization

- Uncontrolled Type 2 diabetes, as defined as most recent historical HbA1c > 10%, or
hospitalization to treat hyper- or hypo-glycemia in the past 3 months

- Diabetic ketoacidosis

- Known hypersensitivity to polystyrene sulfonate

- Significant cardiovascular or cerebrovascular events in the past 2 months

- Severe heart failure, defined as NYHA (New York Heart Association) class IV or
hospitalization to treat heart failure in previous 3 months

- History of bowel obstruction, swallowing disorders, severe gastrointestinal
disorders, or major gastrointestinal surgery

- Major psychiatric disorder (DSM-III-R or DSM-IV) including major depression or other
psychoses that has required hospitalization in the last 3 years. History of attempted
suicide or uncontrolled bipolar disorder.

- Use of an investigational product within 30 days prior to Screening