Vitamin B-6 (pyridoxine)
- Pyridoxine is water-soluble.
- Sources include meat, nuts, and whole-grain products (especially wheat).
- Deficiency usually occurs in conjunction with inadequate intake of other B vitamins due to poor diet or malabsorption states.
- Isolated pyridoxine dependency can occur during treatment with isoniazid, which is a pyridoxine antagonist.
- Pyridoxine requirements are increased in the presence of other drugs, including penicillamine, contraceptive steroids, and hydralazine.
- Clinical features of deficiency in young infants include abnormal CNS activity (eg, irritability, aggravated startle response, seizures) and GI distress (eg, distension, vomiting, diarrhea).
- Other manifestations include anemia, peripheral neuropathy, and dermatitis.
- Treatment consists of pyridoxine 5 mg intramuscularly followed by 0.5 mg per day orally for 2 weeks. Correct dietary deficiency.
- Consider pyridoxine dependency in the differential diagnosis of neonatal seizures when other more common causes have been eliminated. Rapid treatment with pyridoxine, 100 mg intramuscularly, is recommended.
Deficiency causes a pellagra-like syndrome, with seborrheic dermatitis, glossitis, and cheilosis, and, in adults, can cause depression, confusion, EEG abnormalities, and seizures. Rarely, deficiency or dependency causes seizures in infants. Seizures, particularly in infants, may be refractory to treatment with anticonvulsants. Normocytic, microcytic, or sideroblastic anemia can also develop.
Vitamin B6 deficiency should be considered in any infant who has seizures, any patient who has seizures refractory to treatment with anticonvulsants, and any patient with deficiencies of other B vitamins, particularly in patients with alcoholism or protein-energy malnutrition. Diagnosis is usually clinical. There is no single accepted laboratory test of vitamin B6 status; measurement of plasma pyridoxal phosphate is most common.
- Elimination of risk factors when possible
should also be given pyridoxine 30 to 50 mg/day. For deficiency due to increased metabolic demand, amounts larger than the daily recommended intake (DRI) may be required. For most cases of inborn errors of metabolism, high doses of pyridoxine may be effective.
Vitamin B6 Toxicity
The ingestion of megadoses (> 500 mg/day) of pyridoxine (eg, taken to treat carpal tunnel syndrome or premenstrual syndrome although efficacy is unproved) may cause peripheral neuropathy with deficits in a stocking-glove distribution, including progressive sensory ataxia and severe impairment of position and vibration senses. Senses of touch, temperature, and pain are less affected. Motor and central nervous systems are usually intact.
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