Inclusion Criteria:

• Male or female patients
• Aged between 18 and 80 years old at the start of the study.
• Women of child-bearing potential to consent to either abstinence or the use of contraception during the study period
• Patients must have capacity to give written, informed consent to participate in the study prior to commencing the study. They must be fully aware of the aims, nature, planned interventions and potential risks of participating in the study. This consent must be obtained by the time of participant inclusion.
• Established and stable on haemodialysis for at least 2 months
• Thrice weekly haemodialysis
• In possession of permanent dialysis access - either arterio-venous fistula (AVF) or graft (AVG) or permanent dialysis catheter/tunnelled haemodialysis line (THL).
• ESKD not caused by previously diagnosed primary hyperoxaluria.
• Mean baseline serum oxalate level of ≥20 μmol/L
• No recent (within last 2 months) significant changes to regular medications or diet

Exclusion Criteria:

• Known diagnosis of PH1, 2 or 3; or a pathological mutation documented to cause primary hyperoxaluria.
• Established on haemodialysis for less than 2 months.
• On peritoneal dialysis.
• Combined haemodialysis and peritoneal dialysis.
• Temporary or poorly functioning haemodialysis access
• Pregnancy, planning pregnancy or currently breast feeding.
• Co-morbidity of an enteric disorder such as Inflammatory Bowel Disease (IBD), short gut syndrome, or a malabsorptive disorder.
• Decompensated Liver failure.
• Intercurrent active infection and/or antibiotic treatment.
• Currently on Vitamin C treatment with a daily dose of more than 250mg.
• Terminal illness and/or life expectancy of less than 1 year.
• Currently relapsed or uncontrolled and symptomatic psychiatric disorder preventing compliance with the study.
• Participants institutionalised by court or government order.
• Patients who could be coerced due to dependency on the sponsor, the investigator, the trial sites or test centres.
• Deranged liver function tests: If alanine aminotransferase (ALT) or aspartate aminotransferase (AST) is more than twice the upper limit