Vitamin B6

Pyridoxinum

For medical students2 min readUpdated 2026-10-10

Vitamin B6 is a vital bioactive substance derived from pyridine. In clinical practice, the term encompasses a group of related compounds that, once activated, play a fundamental role in amino acid and lipid metabolism, as well as nervous system function.

PreparationsClinical practice uses pyridoxine and the preformed coenzyme pyridoxal phosphate.

Active FormPyridoxal 5'-phosphate (formed in the body via phosphorylation).

NeurotransmittersRegulates the metabolism of GABA, serotonin, histamine, and glycine.

Liver ProtectionReduces the toxicity of specific antitubercular drugs.

Chemical Structure and Activation Mechanism

The term "Vitamin B6" does not refer to a single substance, but rather to a whole group of related compounds: pyridoxine, pyridoxal, and pyridoxamine. Chemically, all of these are pyridine derivatives.

Upon entering the body, the parent molecules lack high biological activity on their own. To participate in biochemical pathways, the substance must undergo an obligatory activation step—phosphorylation. This yields the active coenzyme known as pyridoxal 5'-phosphate (PLP). It is in this form that the vitamin exerts its pharmacodynamic effects at the cellular level.

Pharmacodynamics and Metabolic Effects

The key physiological role of the active coenzyme lies in regulating overall body metabolism.

Protein Metabolism: Vitamin B6 is an indispensable participant in amino acid metabolism. Basic biochemical reactions such as decarboxylation (removal of a carboxyl group) and transamination (transfer of an amino group) cannot occur without it.
Lipid Metabolism: The compound actively participates in regulating fat metabolism, ensuring cellular energy balance.

Any condition accompanied by impaired protein metabolism is a direct indication for including pyridoxine in combination therapy.

Role in the Nervous System

Ensuring the normal functioning of the central nervous system (CNS) and peripheral nervous system (PNS) is one of the primary functions of Vitamin B6. This effect is achieved through the coenzyme's direct involvement in neurotransmitter metabolism.

Pyridoxal 5'-phosphate is critically required for the metabolism of signaling molecules that transmit nerve impulses:

GABA (gamma-aminobutyric acid).
Serotonin.
Histamine.
Glutamic acid.
Glycine.

Natural Sources of the Vitamin

To prevent deficiency states, it is important to know dietary sources of Vitamin B6. It is widely distributed in nature:

Plant Sources: The highest concentrations are found in yeast, whole grains, and legumes (especially beans). Groats (buckwheat, millet) and potatoes are also good sources.
Animal Sources: Liver, various meats, fish, egg yolks, and milk are recommended to meet daily requirements.

Clinical Pharmacology and Indications

In medical practice, medications are administered orally (per os) or parenterally. The main indications span multiple fields:

Deficiency States: Prevention and treatment of Vitamin B6 hypovitaminosis and avitaminosis.
Neurology: Therapy for paresis, paralysis, diabetic neuropathies, and recovery following traumatic brain injury.
Toxicology and Hepatology: Liver protection and prevention of toxic effects associated with antitubercular drugs.
Gastroenterology: Part of combination therapy for peptic ulcer disease and atherosclerosis.
Hematology and Dermatology: Treatment of hypochromic anemia and various skin disorders.

Mnemonic

To easily remember the neurotransmitters influenced by Vitamin B6 metabolism, use the rule of "Four Gs and one S": GABA, Histamine (H), Glutamic acid, Glycine, and Serotonin.

Frequently asked questions

Which specific antitubercular drug toxicity does Vitamin B6 prevent?

Vitamin B6 is co-administered with isoniazid to prevent peripheral neuropathy. It is also used for hepatoprotection and the prevention of toxicity during antitubercular therapy.

What are the clinical symptoms of Vitamin B6 deficiency (hypovitaminosis)?

Clinical symptoms of Vitamin B6 deficiency include neurological, dermatological, and hematological disorders. The main manifestations of hypovitaminosis include:

Neurological signs — polyneuropathy, peripheral neuritis, confusion, and seizures (including in infants).
Skin lesions — development of various forms of dermatitis.
Hematological changes — microcytic anemia.

In which form does Vitamin B6 exert its pharmacological action?

The parent compounds (pyridoxine, pyridoxal) are inactive. They become active only after phosphorylation, converting into the active coenzyme: pyridoxal 5'-phosphate.

Why is pyridoxine prescribed alongside antitubercular drugs?

Specific antitubercular therapy has high systemic toxicity. Vitamin B6 is used for liver protection and to prevent pronounced toxic effects of these drugs on the body.

What role does this vitamin play in amino acid metabolism?

It is an absolutely essential coenzyme for key reactions of protein metabolism—specifically, the decarboxylation and transamination of amino acids.

In which neurological conditions are Vitamin B6 preparations indicated?

They are prescribed for paresis, paralysis, diabetic neuropathies, and for the comprehensive rehabilitation of patients following traumatic brain injuries.

Go deeper

Biochemistry of amino acid decarboxylation and transamination reactions
Role of GABA, glycine, and serotonin in regulating CNS functions
Mechanisms of hypochromic anemia development in B-vitamin deficiencies
Pharmacokinetics: absorption and distribution of pyridine derivatives
Biochemical interactions between pyridoxine and antitubercular agents