USMLE

Vitamin B6 (Pyridoxine)

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Vitamins
  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus

Summary

Vitamin B6 (Pyridoxine) refers to a group of water-soluble vitamins important in metabolic reactions via its active form, PLP (pyridoxal 5′-phosphate). PLP is involved in a number of enzymatic reactions, including transamination, decarboxylation, that of glycogen phosphorylase. PLP is also involved in neurotransmitter synthesis, cystathionine synthesis, histamine synthesis, heme synthesis, and gene expression.

Given its important physiologic roles, Vitamin B6 deficiency can present with many signs and symptoms. Examples include neuropathy (paresthesias), convulsions and a sideroblastic anemia secondary to ALA synthase dysfunction. Vitamin B6 deficiency can be caused by a variety of reasons, but classically is seen in the setting of oral contraceptive or isoniazid use.

Key Points

  • Vitamin B6 (Pyridoxine)
  • Vitamin B6 Deficiency
    • most common in patients taking isoniazid/INH (for TB) or oral contraceptives
      • Isoniazid inhibits pyridoxine phosphokinase, which converts pyridoxine to PLP (active form)
    • Due to its many functions, deficiency presents with many symptoms, including:
      • Peripheral neuropathy
      • Sideroblastic anemias
        • due to role as cofactor for ALA synthase
        • presents as microcytic, hypochromic anemia
      • Convulsions/seizures, hyperirritability, seborrheic dermatitis, glossitis also seen (nonspecific, low-yield)


Find Vitamin B6 and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.