D9961C00001, AZD5492, SLE or IIM

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