This study is a randomized study designed as a 2x2 cross-over in two periods (Period 1 and Period 2) to assess the safety, pharmacokinetics (PK), pharmacodynamics (PD), and efficacy of EOS789 in patients with chronic kidney disease (CKD) and hyperphosphatemia receiving hemodialysis. Period 1 is double-blind and Period 2 is open-label. Period 1 and Period 2 are identical with regard to the design, inclusion/exclusion criteria, and assessments. EOS789 and its combination with sevelamer carbonate are tested in Period 1 and Period 2 respectively.

Inclusion Criteria:

- Patients with CKD and hyperphosphatemia must meet the following criteria for study entry:

• Age ≥18 years
• On thrice-weekly hemodialysis for at least 3 months prior to screening
• Not having changed dialysis prescription within 4 weeks prior to screening for dialyzer, calcium concentration in dialysate, or dry weight more than 1 kg
• Receiving stable doses of treatments affecting serum phosphorus for at least 4 weeks prior to screening and willing to discontinue these treatments

Exclusion Criteria:

- Patients with CKD and hyperphosphatemia who meet any of the following criteria will be excluded from study entry:

• Uncontrolled diabetes and/or hypertension in the opinion of the investigators
• Uncontrolled chronic constipation and/or diarrhea in the opinion of the investigators
• Hospitalization for cardiac disease in previous 3 months
• Evidence of acute or chronic hepatitis or known liver cirrhosis
• Aspartate aminotransferase (AST) and/or alanine aminotransferase (ALT) >2.5 x upper limit of normal (ULN)