Vitamin B6 Toxicity

Pyridoxine, pyridoxamine, pyridoxal, and the phosphorylated derivative of each of these compounds

Symptoms

Vitamin B6 toxicity manifests with peripheral neuropathy, dermatoses, photosensitivity, dizziness, and nausea

Patients will typically present with bilateral sensory or motor changes, although a unilateral presentation is possible if there has been previous trauma or neurologic injury to an extremity.

Sources

  • Pyroxidine and pyridoxamine are found in plant foods

  • Pyroxidal in animal products

  • Cooking, processing and storing reduces availability 10 to 50%

Metabolism

  • Converted in the liver to the active form

  • Catabolised and excreted in urine

Actions

  • Needed in gluconeogenesis

  • Decarboxylates AAs

  • Tryptophan to Niacin

  • Heme synthesis

  • Immune function

  • Neurotransmitter synthesis

  • Steroid and hormone modulation

Deficiency

  • Rare

  • Marginal deficiencies may be more common, manifested as nonspecific stomatitis, glossitis, cheilosis, irritability, confusion, and depression, and possibly peripheral neuropathy

Toxicity

Cases of peripheral neuropathy, dermatoses, photosensitivity, dizziness, and nausea have been reported with long-term megadoses of pyridoxine over 250 mg/day; a few cases of neuropathy appear to have been caused by chronic intake of 100 to 200 mg/day

Cases of acute intoxication typically present with paresthesias, generalized sensory loss, and autonomic dysfunction, without weakness

The clinical picture is similar to that of animal models of pyridoxine toxicity and may be caused by a sensory ganglion neuronopathy

Treatment

There is no specific treatment or antidote for pyridoxine toxicity. Treatment involves cessation of supplemental pyridoxine promptly following diagnosis, symptomatic management, and supportive care for any continued or irreversible symptoms

Prognosis

Prognosis is usually favorable, with symptoms resolving or decreasing when supratherapeutic pyridoxine has been discovered and stopped. 

References