A Clinical Study of TS-172 in Hyperphosphatemia Patients on Peritoneal Dialysis

Inclusion Criteria: 1. Hyperphosphatemia patients (outpatients) with chronic kidney disease receiving peritoneal dialysis (CAPD or APD) at least 12 weeks prior to Visit 1 (Week -4) 2. Patients aged \>= 18 years at the time of obtaining informed consent 3. Patients who are receiving at least one phosphate binder and whose dosing regimen for all phosphate-lowering agents (phosphate binder and tenapanor hydrochloride) has been unchanged during the last 4 weeks prior to Visit 1 (Week -4). 4. Patients with serum phosphorus concentration of \>= 3.5 mg/dL and =\< 7.0 mg/dL at Visit 1 (Week -4) 5. Patients whose serum phosphorus concentration at Visit 2 (Week -2) or Visit 3 (Week -1) or Visit 4 (Week 0) has increased by at least 1.0 mg/dL compared with the value at Visit 1 (Week -4) and is \>= 5.5 mg/dL and \< 10.0 mg/dL. Exclusion Criteria: 1. Patients with confirmed serum intact PTH concentration \>500 pg/mL from Visit 1 (Week -4) to Visit 4 (Week 0) 2. Patients with serum phosphorus concentration \>= 10.0 mg/dL from Visit 2 (Week -2) or Visit 3 (Week -1) 3. Patients who have undergone previous parathyroid intervention (PTx, PEIT, etc.)