Trial on Treatment of Patients With Primary Hyperoxaluria Type I With Pyridoxal-phosphate

Inclusion Criteria: * Documentation of diagnosis of PH I by any one of the following: * Liver biopsy confirmation of deficient liver specific peroxisomal alanine-glyoxylate aminotransferase, (AGT or mislocalization of AGT from peroxisomes to mitochondria) * Homozygosity or compound heterozygosity for a known mutation in the causative gene (AGXT) for PH I * Male or female subjects between 5 years and 60 years of age * Renal function defined as an estimated GFR \> 60 ml/min normalized to 1.73 m2 body surface area * Subjects receiving pyridoxal-phosphate before the study must be willing to discontinue therapy with pyridoxal-phosphate for a wash out phase of at least 4 weeks but always until normalization of serum pyridoxal-phosphate levels * Written informed consent from patients and/or legally acceptable representatives Exclusion Criteria: * Pregnant or lactating women * Women of child-bearing potential who are not using a highly effective contraception method with a pearl-index \< 1. Highly effective contraception methods are oral, transdermal, injectable, or implanted contraceptives, IUD, abstinence, or sterile sexual partner and must agree to continue using such precautions during the pyridoxal-phosphate study * Subjects post liver or kidney transplantation or combined transplantation * Chronic diarrhoea with the risk of malabsorption * Any other abnormal finding such as physical examination or laboratory evaluation, in the opinion of the investigator, is indicative of a disease that would compromise the safety taking pyridoxal-phosphate per os and the absorption * Subjects participating in other clinical trials with investigational products 4 weeks prior to trial entry, during the trial and 4 weeks after the trial * Subjects who are unable to take the trial medication * Subjects who are unable to collect 24-hour urine samples or follow other study procedures * Subjects who are under treatment with L-Dopa, Isoniazid, D-Penicillamine (interactions between these drugs and pyridoxal-phosphate are known and might influence serum pyridoxal-phosphate levels) * Subjects with known allergies to substances of contents (e.g. Potassium sorbet, raspberry syrup) * Subjects confined to an institution on judicial or official behalf * Subjects who are in dependency to the sponsor or the PI of the trial