Vitamin B6 toxicity
In experimental animals, doses of vitamin B6 of 50 mg/kg body weight cause histological damage to dorsal nerve roots, and doses of 200 mg/kg body weight lead to the development of signs of peripheral neuropathy, with ataxia, muscle weakness, and loss of balance. The clinical signs of vitamin B6 toxicity in animals regress within 3 months after withdrawal of these massive doses, but sensory nerve conduction velocity, which decreases during the development of the neuropathy, does not recover fully.
Sensory neuropathy has been reported in seven patients taking 2–7 g of pyridoxine/day. Although there was some residual damage, withdrawal of these extremely high doses resulted in a considerable recovery of sensory nerve function. Other reports have suggested that intakes as low as 50 mg/day are associated with neurological damage, although these studies were based on patients reporting symp-toms rather than objective neurological examination. There have been no reports of nerve damage in chil-dren with vitamin B6-dependent homocystinuria, or other inborn errors of metabolism, who take 200–300 mg/day.