In this study the investigators will prospectively analyze the reduction of urinary oxalate excretion under the treatment with PLP in dosages of 5mg/kg/day up to 20 mg/kg/day and serum level response relationship with PLP as an i.v. solution used orally in 12 patients with primary hyperoxaluria type I as an inherited autosomal-recessive-disorder leading to increased endogenous oxalate production, urolithiasis and end stage renal disease.

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