Chemical Structure and Analogues
The thiamine molecule consists of two rings—a pyrimidine and a thiazole ring—connected by a methylene bridge.
In pharmacological practice, the vitamin B₁ group is represented by several agents:
- Thiamine — the basic water-soluble substance.
- Benfotiamine — a lipid-soluble analogue with different pharmacokinetics.
- Cocarboxylase — the preformed coenzyme form.
- Monophosphothiamine.
Fun fact: There are compounds containing a thiamine molecular fragment that lack vitamin properties. For example, clomethiazole is an agent with sedative, hypnotic, muscle relaxant, and anticonvulsant properties. Its mechanism is fundamentally different and involves 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 via phosphorylation. This yields the active form—thiamine diphosphate, better known as cocarboxylase.
The mechanism of action of cocarboxylase is based on its role as a coenzyme in numerous enzymatic reactions. A key example of this interaction is its participation in the decarboxylation of $\alpha$-keto acids, which is a crucial step in carbohydrate metabolism.
Pharmacological Effects
The drug's effects span multiple body systems:
- Metabolic effect: thiamine participates in the metabolism of all major nutrients—carbohydrates, proteins, and lipids.
- Neurotropic effect: the drug directly regulates nerve impulse transmission at synapses.
- Specific properties: exerts pronounced antineuritic and antioxidant effects.
Clinical Presentation of Deficiency
Vitamin B₁ deficiency leads to metabolic disruption and the accumulation of toxic metabolic products in tissues (specifically, $\alpha$-keto acids).
- Hypovitaminosis (insufficiency): manifests with neurological symptoms (polyneuritis, muscle weakness) and cardiac symptoms caused by the accumulation of cardiotoxic metabolites.
- Avitaminosis (complete deficiency): leads to a severe disease known as beriberi. It is characterized by profound damage to the central and peripheral nervous systems, as well as severe cardiovascular dysfunction.
Indications for Use
The prescription of thiamine preparations is indicated in the following cases:
- Deficiency states: for the treatment and prevention of hypovitaminosis and avitaminosis.
- Neurology: as part of combination therapy for central and peripheral nervous system disorders.
- Cardiology: for myocardial dystrophy and cardiac arrhythmias (to eliminate the cardiotoxic action of metabolites).
- Physiological states with increased demand: pregnancy, lactation.
- Stresses: heavy physical labor, extreme bodily stress.
Dosage Forms and Administration
The drug is administered both enterally (orally) and parenterally (intramuscularly).
Dosage forms:
- Tablets and coated tablets of 0.00258 g.
- Tablets of 0.00645 g and 0.0129 g.
- 3% and 6% solutions in 1 ml ampoules.
Dosages:
- Oral (per os): from 0.00258 to 0.0129 g.
- Intramuscular: from 0.03 to 0.06 g.