Why is pyridoxine (Vitamin B6) given in toxic alcohol poisoning?

Pyridoxine in Toxic Alcohol Poisoning

Pyridoxine (vitamin B6) is administered in ethylene glycol poisoning at a dose of 50 mg IV every 6 hours to improve the conversion of glyoxylic acid into glycine, reducing the formation of toxic metabolites. 1

Mechanism of Action

• Ethylene glycol itself is not highly toxic, but its metabolites (glycoaldehyde, glycolic acid, glyoxylic acid, and oxalic acid) cause life-threatening metabolic acidosis and renal failure 2
• Pyridoxine acts as a cofactor to enhance the conversion of glyoxylic acid to glycine, which is less toxic than the alternative metabolite, oxalic acid 3
• This metabolic pathway diversion reduces the formation of calcium oxalate crystals that can cause renal tubular damage 3

Dosing in Ethylene Glycol Poisoning

• The recommended dose for ethylene glycol poisoning is 50 mg IV every 6 hours 1
• This is part of a comprehensive treatment approach that includes:
  • ADH inhibition with fomepizole or ethanol to prevent metabolism of ethylene glycol 4
  • Correction of metabolic acidosis 5
  • Hemodialysis in severe cases to remove both parent compound and toxic metabolites 1

Clinical Evidence and Rationale

• Pyridoxine is recommended as a cofactor therapy in ethylene glycol poisoning to improve the conversion of toxic metabolites to less harmful compounds 3
• The primary treatment focuses on inhibiting alcohol dehydrogenase with either:
  • Fomepizole (4-methylpyrazole), which has a more predictable metabolism and fewer side effects 6
  • Ethanol, which saturates alcohol dehydrogenase but requires careful monitoring due to its own toxicity 2
• Hemodialysis is indicated in severe cases with significant acidosis or renal dysfunction 1

Important Considerations

• Pyridoxine is highly dialyzable, with in vivo clearance averaging 170 mL/min with cellulose filter membranes 1
• During hemodialysis, supplemental doses of pyridoxine may be required due to its high dialyzability 1
• Pyridoxine supplementation is particularly important in patients with alcoholism, who may have underlying vitamin B6 deficiency 7

Monitoring and Safety

• Pyridoxine is generally safe at the doses used for toxic alcohol poisoning 7
• Long-term high-dose pyridoxine (>300 mg/day) should be avoided due to potential neurotoxicity 7
• Monitor for improvement in acid-base status and renal function during treatment 6

Comparison with Other Indications for Pyridoxine

• Pyridoxine is also used in other toxicological emergencies:
  • Isoniazid overdose: 1 g of pyridoxine for each gram of isoniazid ingested (up to 5 g maximum) 1, 8
  • Gyromitra mushroom poisoning (monomethylhydrazine) 3
  • Hydrazine exposure 3

Pyridoxine is an important adjunctive therapy in toxic alcohol poisoning, working alongside primary treatments like ADH inhibitors and hemodialysis to reduce the formation of harmful metabolites and improve patient outcomes 3.