Chemical structure and analogs
The thiamine molecule consists of two rings — a pyrimidine ring and a thiazole ring, which are connected by a methylene bridge.
In pharmacological practice, the vitamin B₁ group is represented by several drugs:
- Thiamine is the basic water-soluble substance.
- Benfotiamine is a fat-soluble analog with different pharmacokinetics.
- Cocarboxylase is the preformed coenzyme form.
- Monophosphothiamine.
Interesting fact: There are drugs that contain a thiamine molecule fragment in their structure but do not possess vitamin properties. For example, chlormethiazole is an agent with sedative, hypnotic, muscle relaxant, and anticonvulsant activity. Its mechanism is fundamentally different and is associated with increasing the sensitivity of GABA receptors to the neurotransmitter.
Pharmacokinetics and mechanism of action
Thiamine itself is a prodrug. Upon entering the body, it undergoes metabolic activation — phosphorylation. As a result, the active form is produced — thiamine diphosphate, better known as cocarboxylase.
The mechanism of action of cocarboxylase is that it acts as a coenzyme in numerous enzymatic reactions. A key example of such interaction is its participation in the decarboxylation of $\alpha$-keto acids, which is a crucial stage of carbohydrate metabolism.
Pharmacological effects
The drug's action covers several body systems:
- Metabolic action: thiamine is involved in the metabolism of all major nutrients — carbohydrates, proteins, and fats.
- Neurotropic action: the drug directly regulates the conduction of nerve excitation in synapses.
- Specific properties: it exerts pronounced antineuritic as well as antioxidant effects.
Clinical presentation of deficiency
Vitamin B₁ deficiency leads to metabolic disruption and the accumulation of toxic metabolic products (specifically, $\alpha$-keto acids) in tissues.
- Hypovitaminosis (insufficiency): manifests with neurological symptoms (polyneuritis, muscle weakness) and cardiac symptoms arising from the accumulation of cardiotoxic metabolites.
- Avitaminosis (complete absence): leads to the development of a severe condition — beriberi disease. It is characterized by severe damage to the central and peripheral nervous systems, as well as profound impairments of cardiovascular function.
Indications for use
The prescription of thiamine preparations is justified in the following cases:
- Deficiency states: for the treatment and prevention of hypovitaminosis and avitaminosis.
- Neurology: in combination therapy for pathologies of the central and peripheral nervous system.
- Cardiology: for myocardial dystrophy and cardiac rhythm disorders (to eliminate the cardiotoxic action of metabolites).
- Physiological states with increased demand: pregnancy, lactation period.
- Exertion: heavy physical labor, extreme bodily states.
Dosage forms and regimen
The drug is administered both enterally (orally) and parenterally (intramuscularly).
Formulations:
- Tablets and dragées 0.00258 g.
- Tablets 0.00645 g and 0.0129 g.
- Solution in 3% and 6% ampoules of 1 ml.
Dosages:
- Orally (per os): from 0.00258 to 0.0129 g.
- Intramuscularly: from 0.03 to 0.06 g.
Briefly: answers to topical questions
How does benfotiamine differ from thiamine?
Benfotiamine differs from thiamine in that it is a fat-soluble analog of the latter. Thiamine is listed as the base substance of the vitamin B₁ group of drugs.
| Characteristic | Thiamine | Benfotiamine |
|---|---|---|
| Chemical nature | Base substance | Thiamine analog |
| Solubility | Water-soluble vitamin B₁ | Fat-soluble analog |
In the body, thiamine is phosphorylated, turning into the active form — thiamine diphosphate, or cocarboxylase.
In which enzymatic reactions, besides the decarboxylation of alpha-keto acids, does cocarboxylase participate?
In addition to the decarboxylation of α-keto acids, the active form of vitamin B₁ — thiamine diphosphate, or cocarboxylase — participates in transketolase reactions.
- Transketolase is an enzyme of the non-oxidative stage of the pentose phosphate pathway; its coenzyme is thiamine diphosphate.
- The non-oxidative stage includes reversible reactions of transferring 2- and 3-carbon fragments from one molecule to another.
These reactions are associated with the synthesis of pentoses or the return of carbon atoms to the hexose pool when pentoses are in excess.
Thiamine is Fuel for the nerves. Without B1, toxic "garbage" (keto acids) accumulates, the heart weakens, and the nerves fail (beriberi).
Class and exam questions
What is the difference between thiamine and cocarboxylase?
Thiamine is a base substance that gets phosphorylated in the body and turns into its active coenzyme form — cocarboxylase (thiamine diphosphate).
Why does vitamin B1 deficiency affect the heart?
Thiamine deficiency disrupts carbohydrate metabolism (decarboxylation of α-keto acids). This leads to the accumulation of cardiotoxic metabolites in the body, causing myocardial dystrophy and arrhythmias.
Does chlormethiazole possess vitamin activity?
No. Although chlormethiazole contains a thiamine molecular fragment, it does not possess vitamin B1 properties. Its effects (sedative, hypnotic) are associated with its action on GABA receptors.
How is thiamine related to the antiseptic hexetidine (Hexoral)?
Hexetidine is a structural antagonist of thiamine. By replacing it, it disrupts bacterial oxidation reactions and metabolism, providing an antibacterial effect.
What else to study on this topic
- The biochemical cascade of $\alpha$-keto acid decarboxylation and the role of cocarboxylase.
- Comparative pharmacokinetics of water-soluble thiamine and fat-soluble benfotiamine.
- Pathogenesis of neurological disorders in beriberi disease.
- The use of vitamin antagonists as antimicrobial agents (using hexetidine as an example).
- Interaction of thiamine with other B-complex vitamins in the combination therapy of polyneuritis.
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