The hydrochloride salt of pyridoxine, a water-soluble B vitamin. Pyridoxine is converted in the liver into the metabolically active coenzyme form pyridoxal 5'-phosphate (P5P), an essential cofactor in many enzymatic reactions in amino acid metabolism, including transamination, deamination, and decarboxylation. P5P is required for glycogenolysis and the synthesis of sphingolipids and is essential to red blood cell, nervous system, and immune system functions.