Randomized. double blind, placebo controlled, parallel arms dose finding study with a 4 weeks treatment period

The study consists of a screening period of approximately 1 week, a wash out period of up to 3 weeks, where existing phosphate lowering medication is withheld, a 4-week treatment period and a follow-up period of up to 2 weeks, during which patients are put back on their pre washout phosphate lowering medication.

The wash out period will be either 1 week, 2 weeks or 3 weeks depending on the increase in s-phosphate levels.

There are 7 parallel treatment arms in the study with bid and od treatment regimens.

Laboratory efficacy endpoints and safety assessments will be evaluated at various times throughout the study.

The target population of the study is: male or female patients, above18 years of age with End Stage Renal Disease (ESRD) on chronic maintenance hemodialysis (HD) 3 times a week for a minimum of 3 months.

Inclusion Criteria:

1. Females and males aged ≥18 years
2. Chronic maintenance hemodialysis 3 x/week for a at least 3 months
3. Prescribed and taking at least 3 doses of phosphate binder per day
4. Serum phosphate levels should be between 3.5 and 8.0 mg/dL ; 1.13 mmol/L and 2.58 mmol/L (inclusive) at screening
5. Total serum calcium levels 2.0 - 2.6 mmol/L inclusive at screening
6. For randomization in the study, after up to 3 weeks wash out of phosphate binders, patients must have serum phosphate levels of at least 6. 0 mg/dL (1.94 mmol/L) but below 10 mg/dL (3.23 mmol/L) and have had an increase of at least 1.5 mg/dL (0.48 mmol/L) vs pre wash out

Exclusion Criteria:

1. Severe hyperphosphatemia defined as >10 mg/dL on Phosphate-binders at all time points during clinical routine monitoring for the 3 preceding months before screening visit.

2. Serum parathyroid hormone >1200 pg/mL

3. Significant metabolic acidosis

4. Clinical signs of hypovolemia at randomization

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