Vitamin B6 refers to six compounds (vitamers), including pyridoxine, pyridoxal, and pyridoxamine. The active coenzyme forms are pyridoxal 5′-phosphate (PLP) and pyridoxamine 5′-phosphate (PMP). Pyridoxine functions as a coenzyme in metabolic processes involving carbohydrates, lipids, and amino acids. Deficiency of vitamin B6 can result from malabsorption, malignancies, and long-term drug use.
Clinical Pharmacology:
Pyridoxine is found in plants, while pyridoxal and pyridoxamine are found in animals. These forms are converted into pyridoxal phosphate by pyridoxal kinase. Riboflavin is required for the conversion of pyridoxine phosphate into pyridoxal phosphate. The total body pool of vitamin B6 ranges from 16 to 25 mg, with most stored in the liver. It plays an essential role in the synthesis of neurotransmitters like serotonin and dopamine, and in immune function.
Indications and Usage:
Pyridoxine Hydrochloride Injection is used to treat deficiency caused by inadequate diet, drug-induced deficiency, and genetic disorders. It also reduces pregnancy-induced nausea and is used in the treatment of hyperhomocysteinemia. Vitamin B6 may help lower the risk of cancer, cognitive decline, and premenstrual syndrome.
Contraindications:
Vitamin B6 is contraindicated in individuals with hypersensitivity to the preparation.
Warnings:
Long-term use of high doses of vitamin B6 (>2 g/day) can cause permanent peripheral neuropathy. Doses above 200 mg/day may lead to dependence. Some preparations of pyridoxine contain aluminum, which may be toxic.
Precautions:
High doses of pyridoxine can interact with levodopa, anticonvulsants, and ethanol, reducing their effects. Pyridoxine may cause photosensitivity when taken with amiodarone.
Adverse Reactions:
Undiluted i.v. injections of pyridoxine can cause dizziness and tissue irritation. High doses can cause vertigo, cramps, and long-term use may lead to sensory neuropathy.
Overdosage:
Excessive doses of pyridoxine can result in overdose neuropathy syndrome, with symptoms including paraesthesia, hyperaesthesia, and muscle weakness.