Study to Evaluate the Efficacy and Safety of Oxabact (OC5) in Patients With Primary Hyperoxaluria

Inclusion Criteria: * Signed informed consent (as applicable for the age of the subject). * Male or female subjects ≥ 2 years of age (Germany \& France) / Male or female subjects ≥ 5 years of age (United Kingdom) * A diagnosis of PH type I, II or III (as determined by standard diagnostic methods). * A mean urinary oxalate excretion of \> 1.0 mmol/24h/1.73m2, based on at least three eligible urine collections performed during baseline (weeks 1-4). * Renal function defined as an estimated GFR ≥ 40 ml/min normalised to 1.73m2 body surface area, or a creatinine clearance of ≥ 40 ml/min normalised to 1.73m2 body surface area. * Subjects receiving vitamin B6 must be receiving a stable dose for at least 3 months prior to screening and must not change the dose during the study. Subjects not receiving vitamin B6 at study entry must be willing to refrain from initiating pyridoxine during study participation. Exclusion Criteria: * Inability to collect complete 24-hour urine samples. Each urine collection will be evaluated for completeness based on urine qualitative criteria. * Inability to swallow size 4 capsules twice daily for 8 to 10 weeks. * Subjects that have undergone transplantation (solid organ or bone marrow). * The existence of secondary hyperoxaluria, e.g. hyperoxaluria due to bariatric surgery or chronic gastrointestinal diseases such as cystic fibrosis, chronic inflammatory bowel disease and short-bowel syndrome. * Use of antibiotics to which O. formigenes is sensitive, including chronic use, a history of more than two courses of antibiotic use during the past 6 months, current antibiotic use, or antibiotics use within 14 days of initiating study medication. * Subjects who require immune suppressive therapy. * Current treatment with ascorbic acid preparation. * Pregnancy. * Women of child-bearing potential who are not using adequate contraceptive precautions such as oral, transdermal, injectable, or implanted contraceptives, IUD, complete abstinence, use of a condom by the sexual partner, or sterile sexual partner. * Presence of a medical condition that the Principal Investigator considers likely to make the subject susceptible to adverse effect of study treatment or unable to follow study procedures. * Participation in any study of an investigational product, biologic, device, or other agent within 30 days prior to screening or not willing to forego other forms of investigational treatment during this study.