To evaluate the effect and safety of KHK7791 in combination with phosphate binders to treat Hyperphosphatemia in ptatients on HD.

Inclusion Criteria:

• Patients with stable chronic renal failure who have undergone hemodialysis three times per week for at least 12 weeks until screening examination.
• Dialysis conditions (dialysate, dialyzer, frequency of dialysis per week, dialysis duration, blood flow rate, and dialysate and substitution fluid flow rates), excluding dry weight, should have been unchanged during the last 2 weeks before screening examination.
• Taking phosphate binders three times per day. The prescribed drug and dosage regimen should have been unchanged during the last 2 weeks before screening examination.
• Serum phosphorus levels should be in the range of ≥6.1 and ≤10.0 mg/dL at screening examination.
• If on any vitamin D or calcimimetics regimen, then the prescribed drug and dosage regimen should have been unchanged for the last 4 weeks before screening examination.

Exclusion Criteria:

• iPTH >600 pg/mL (should be based on the most recent value from the patients' medical records, etc. before pre-enrollment)
• Having concurrent or a history of inflammatory bowel disease (IBD) or diarrhea-predominant irritable bowel syndrome
• History of gastrectomy or enterectomy (excluding endoscopic resection and cecectomy) or having undergone gastrointestinal tract surgery within 3 months before screening examination.
• Having concurrent severe heart disease [including congestive heart failure, defined as New York Heart Association (NYHA) cardiac functional classification of class III or IV, and cardiovascular disease requiring hospitalization, such as myocardial infarction] or hepatic impairment (including AST/ALT ≥100 U/L at screening examination, or cirrhosis).
• Developed cerebrovascular disease (such as cerebral infarction and hemorrhage) or cardiovascular disease (such as myocardial infarction and unstable angina) requiring hospitalization within 6 months before screening examination.
• Uncontrollable hypertension or diabetes.
• Scheduled for living donor kidney transplant, change in the mode of dialysis, home hemodialysis, or change in the dialysis center (relocate to another hospital/clinic) during the study period.
• Any diagnosis of and treatment of malignancy within 5 years before screening examination (excluding basal cell carcinoma or surgically resected intraepithelial carcinoma of uterine cervix).