What is the treatment for a vitamin B6 (pyridoxine) overdose?

Treatment for Vitamin B6 (Pyridoxine) Overdose

The primary treatment for vitamin B6 (pyridoxine) overdose is immediate discontinuation of all vitamin B6 supplementation, followed by symptomatic management of neuropathic pain with appropriate medications such as gabapentin, pregabalin, or duloxetine. 1

Clinical Presentation of Vitamin B6 Toxicity

Vitamin B6 toxicity typically presents with:

• Sensory neuropathy (predominant manifestation)
• Paresthesia and hyperesthesia (particularly in extremities)
• Numbness and tingling in hands and feet
• Bone pain
• Muscle weakness
• Fasciculations
• Loss of deep tendon reflexes
• Motor ataxia 1, 2

These symptoms are typically bilateral unless there is a history of previous trauma to a limb 2.

Diagnostic Approach

• Confirm diagnosis through:
  • History of vitamin B6 supplementation
  • Elevated plasma pyridoxal phosphate (PLP) levels (normal range: 5-50 μg/L or 20-200 nmol/L)
  • In critically ill patients or those with inflammation, red cell PLP should be measured instead 1

Treatment Algorithm

1. Immediate discontinuation of all vitamin B6 supplementation

   • This is the most critical step in management 1

2. Symptomatic management of neuropathic pain

   • First-line medications:

     • Gabapentin: Start 300 mg once daily, target 300-600 mg three times daily
     • Pregabalin: Start 75 mg twice daily, target 150-300 mg twice daily
     • Duloxetine: 60 mg once daily 1

   • Second-line options:

     • Amitriptyline: Start 10-25 mg at bedtime, target 25-100 mg
     • Nortriptyline: Start 10-25 mg at bedtime, target 25-100 mg 1

   • For refractory cases:

     • Consider low-dose naltrexone 1

3. Patient monitoring and follow-up

   • Monitor symptom improvement
   • Understand that axonal regeneration takes time
   • Some patients may have persistent symptoms requiring long-term management 1

Important Considerations

• Recovery timeline: Complete recovery typically occurs within 6 months of stopping vitamin B6 supplementation 2

• Washout period: A washout period of 20-40 days is required for complete clearance of vitamin B6 from the body 3

• Mechanism of toxicity: Pyridoxine (inactive form) competitively inhibits the active pyridoxal-5'-phosphate, paradoxically causing symptoms similar to vitamin B6 deficiency 4

• Risk factors for toxicity:

  • Doses >500 mg/day commonly cause toxicity
  • Long-term doses as low as 100 mg/day have been associated with spinal cord effects
  • The No Observed Adverse Effect Level (NOAEL) is 100 mg/day 1, 5
  • Duration of intake is a significant factor (mean duration in patients with neurotoxicity: 2.9 ± 1.9 years) 2

Prevention of Vitamin B6 Toxicity

• Adhere to safe upper limits:

  • 100 mg/day for adults aged 19+ years 1
  • 80 mg/day for adolescents aged 14-18 years 1

• Be vigilant with patients on long-term supplementation, particularly those who have undergone bariatric surgery, as they may be at higher risk of vitamin B6 overload due to inadequate multivitamin formulations 6

• Regular monitoring of vitamin B6 levels in patients on long-term supplementation 7

The prognosis for vitamin B6 toxicity is generally good with prompt discontinuation of the supplement, though recovery may take several months as the nervous system heals.