The goal of this clinical trial is to learn if AP301 could work in the patients receiving maintenance dialysis with elevated blood phosphate. The main questions it aims to answer are:

• Does AP301 lower blood phosphate levels?
• Does AP301 works on serum calcium level, calcium times phosphate level, and intact parathyroid hormone level?
• What discomfort or medical problem do the patients have when taking AP301?
• Does AP301 improve quality of life in Chinese patients?

The researchers will compare AP301 to an ineffective comparator (a look-alike substance that contains low dose AP301) to see if AP301 works to treat elevated blood phosphate.

In the study, the patients will experience the following stages in a chronicle order:

• Stop all using blood phosphate-lowering drugs,
• Take AP301 or the comparator three times a day for 8 weeks,
• Take AP301 three times a day for 24 weeks, and
• Take AP301 or the comparator three times a day for 3 weeks.

In the first 32 weeks, the dose of AP301 will be adjusted upwards or downwards based on the patient's blood phosphate level and the study doctor's judgment.

If the participant has a blood phosphate level above or below a certain level, they may receive additional treatment to lower the blood phosphate level.

Key Inclusion Criteria:

• Provision of signed and dated ICF

• Age ≥ 12 years when signing the ICF

• Patients on dialysis for ≥ 3 months before signing the ICF and throughout the study

• For HD patients, spKt/V ≥ 1.2; for PD patients, total Kt/V ≥ 1.7/week

• Patients who receive phosphate-lowering drugs over 4 weeks and their serum phosphate level is:

  1. Screening: 1.13 mmol/L (3.5 mg/dL) ≤ serum phosphate < 2.58 mmol/L (8.0 mg/dL)
  2. After washout: 1.94 mmol/L (6.0 mg/dL) ≤ serum phosphate < 3.23 mmol/L (10.0 mg/dL)

Key Exclusion Criteria:

• History or plan of kidney transplantation
• History or plan of parathyroid intervention 6 months before signing the ICF
• Serum calcium < 1.9 mmol/L (7.6 mg/dL) or > 2.75 mmol/L (11 mg/dL) at screening
• Serum intact parathyroid hormone > 127 pmol/L (1200 pg/mL) at screening
• Presence of clinically significant gastrointestinal (GI) disorder
• History of gastrectomy or duodenectomy, or GI surgery within 3 months before signing the ICF
• Known allergic to any ingredient of AP301, or known history of severe allergies leading to emergency medical care
• Female who are breastfeeding