An open-label, single-arm 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.)