From the Guidelines
For patients with Hyperoxaluria, a maximum dose of 5 mg/kg of vitamin B6 (pyridoxine) is recommended to reduce urinary oxalate excretion, with close monitoring for potential neurotoxicity at high doses. This recommendation is based on the most recent and highest quality study available, which suggests that doses above 5 mg/kg do not provide additional benefits and may increase the risk of adverse effects 1. The study also notes that pyridoxine responsiveness, defined as a >30% decrease in urinary oxalate excretion, is most often achieved in patients with specific genetic mutations, such as p.Gly170Arg and p.Phe125Ile mutations.
Key considerations for vitamin B6 supplementation in Hyperoxaluria include:
- Starting with a dose of 5 mg/kg and monitoring urinary oxalate levels to assess responsiveness
- Limiting the dose to 5 mg/kg to minimize the risk of neurotoxicity
- Monitoring patients closely for signs of pyridoxine toxicity, such as nerve tingling or numbness
- Maintaining adequate hydration and following dietary recommendations to further manage oxalate levels
It is essential to note that the effectiveness of vitamin B6 supplementation may vary depending on the individual patient's genetic profile and response to treatment. Therefore, close monitoring and regular assessment of urinary oxalate levels are crucial to determine the optimal dose and duration of treatment 1. Additionally, the study suggests that patients with Hyperoxaluria should be tested for pyridoxine responsiveness, and urine oxalate measurements should be repeated on at least two occasions after at least 2 weeks of pyridoxine administration to evaluate its effectiveness 1.
From the Research
Role of Vitamin B6 in Reducing Oxalate in Urine
The role of Vitamin B6 (Pyridoxine) in reducing oxalate in urine, specifically in cases of Hyperoxaluria, has been investigated in several studies.
- Vitamin B6 has been used for over 40 years to treat Primary Hyperoxaluria Type I (PH I), a condition caused by a deficiency of the liver-specific enzyme alanine-glyoxylate:aminotransferase (AGT) 2.
- A prospective trial studied the effect of increasing dosages of Vitamin B6 on urinary oxalate excretion in 12 patients with genetically confirmed PH I, and found a mean relative reduction in urinary oxalate excretion of 25.5% 2.
- Another study compared the effects of dietary modification, Vitamin B6 and magnesium supplementation, and a combination of both on urinary oxalate excretion in patients with idiopathic hyperoxaluria, and found that a low-oxalate diet was more effective than Vitamin B6 and magnesium supplementation in reducing urinary oxalate excretion 3.
Mechanism of Action
The mechanism of action of Vitamin B6 in reducing oxalate in urine is not fully understood, but it is thought to involve the activation of the enzyme alanine-glyoxylate:aminotransferase (AGT) 2.
- A study found that Vitamin B6 supplementation decreased urinary oxalate excretion by approximately 15% in a rodent model of enteric hyperoxaluria, and that serum pyridoxal 5'-phosphate (PLP) levels explained 63% of the variability in urinary oxalate excretion 4.
- Another study found that Vitamin B6 metabolites, such as pyridoxal 5'-phosphate, were lower in idiopathic calcium stone formers with hyperoxaluria than in healthy subjects, but that there was no correlation between Vitamin B6 metabolites and urinary oxalate excretion 5.
Clinical Applications
Vitamin B6 has been used as a therapeutic agent in the treatment of Primary Hyperoxaluria Type I (PH I) and other forms of hyperoxaluria.
- A case report described a patient with PH I who responded to Vitamin B6 treatment after kidney transplantation, with a reduction in serum creatinine and urinary oxalate excretion 6.
- The study highlights the potential benefits of using Vitamin B6 in combination with other treatments, such as kidney transplantation, in the management of PH I and other forms of hyperoxaluria.