Dose-dependent expression of neuronopathy after experimental pyridoxine intoxication

We examined the sequence of nervous system abnormalities that resulted when rats were given excess amounts of vitamin B6 (pyridoxine). High doses of pyridoxine (1,200 or 600 mg/kg/d) for 6 to 10 days caused a neuronopathy with necrosis of dorsal root ganglion (DRG) sensory neurons, accompanied by centrifugal axonal atrophy and breakdown of peripheral and central sensory axons. Large diameter neurons with long processes and large cytoplasmic volumes were especially affected. Smaller doses (300 to 150 mg/kg/d) for up to 12 weeks had minor effects on DRG neurons, but produced a neuropathy with axonal atrophy and degeneration. Guinea pigs given 1,800 mg/kg/d developed sensory neuronopathy, whereas mice given similar or higher doses did not have neuropathologic abnormalities. Multiple factors including rate of administration, differential neuronal vulnerability, and species susceptibility have bearing on the final expression of pyridoxine neurotoxicity.