What is the workup and treatment for hypervitaminosis B6 (Vitamin B6 toxicity)?

Workup and Treatment for Hypervitaminosis B6

The primary treatment for vitamin B6 toxicity is immediate discontinuation of all vitamin B6 supplements and monitoring for symptom improvement, as there is no specific antidote for this condition.

Clinical Presentation

• Hypervitaminosis B6 typically presents as a peripheral neuropathy that is sensory predominant and length-dependent, characterized by paresthesias, numbness, and pain in the extremities 1, 2
• In severe cases, motor deficits can also occur, including muscle weakness and gait disturbances 3
• Symptoms may develop even with relatively modest doses of vitamin B6 supplementation, not just with mega-doses 1
• The condition can occur from both prescription medications and over-the-counter supplements containing vitamin B6 2

Diagnostic Workup

• Serum vitamin B6 level measurement is the primary diagnostic test, with levels above the reference range (>125 nmol/L) suggesting toxicity 1
• Detailed medication history focusing on all supplements, multivitamins, and over-the-counter medications that may contain vitamin B6 (pyridoxine) 2
• Nerve conduction studies to document the pattern and severity of neuropathy, typically showing an axonal sensorimotor polyneuropathy 4, 3
• Clinical neurological examination focusing on sensory function (vibration, proprioception), motor strength, and deep tendon reflexes 4
• Rule out other causes of peripheral neuropathy including diabetes, alcohol use, nutritional deficiencies, and other toxic exposures 4

Treatment Protocol

1. Immediate discontinuation of all vitamin B6 supplements and medications containing pyridoxine 2
2. Monitor serum vitamin B6 levels until they return to normal range (20-125 nmol/L) 1
3. Supportive care for neuropathic symptoms:
   • Neuropathic pain medications if needed (gabapentin, pregabalin, duloxetine)
   • Physical therapy for motor deficits or gait disturbances 3
4. Patient education about avoiding future vitamin B6 supplementation or limiting to recommended daily allowances 5
5. Follow-up neurological examinations to monitor recovery, which may be slow and incomplete in severe cases 3

Prognosis and Recovery

• Recovery is variable and depends on the severity and duration of toxicity 2
• Improvement typically begins within weeks to months after discontinuation of vitamin B6 2
• Complete recovery may take months to years, and some patients may have permanent neurological deficits in severe cases 3
• Patients with moderately elevated levels (100-200 μg/L) may not show significantly worse neuropathy signs or symptoms compared to those with normal levels 4

Prevention

• Adhere to recommended daily intake of vitamin B6: 1.3-1.7 mg/day for adults aged 14-70 years 6
• The upper tolerable intake level is 100 mg/day for adults over 19 years 6
• For infants, avoid vitamin B6 intake exceeding 1.0 mg/kg/day due to potential toxicity 7
• Patients taking tuberculosis medications (isoniazid) should receive pyridoxine supplementation at 25-50 mg/day to prevent neuropathy, but this should be increased to 100 mg/day only if peripheral neuropathy develops 7

Special Considerations

• Elderly individuals may be more susceptible to vitamin B6 toxicity due to age-related changes in metabolism 7
• Patients with renal impairment may have reduced clearance of vitamin B6, potentially increasing the risk of toxicity 6
• Patients should be cautioned about self-medication with over-the-counter supplements containing vitamin B6 2