Tabex is an original Bulgarian drug of vegetal origin for treatment of nicotinism. It is developed on the basis of the alkaloid contained in the plant Cytisus laburnum L., also called Golden Rain, widespread in the southern areas of Central Europe and Italy. All parts of the plant contain the alkaloid Cytisine, the greatest amount (up to 3%) being found in the seeds.
Fig. 1 Structural formula of cytisine
Chemical characteristics and content of Tabex
Each tablet contains 0.0015 g cytisine
Empirical formula of cytisine: C11H14ON2
Ensuing from the molecular orbital calculations after Kier (1969), it is evident that the molecular configurations of nicotine and acetylcholine have a quaternary nitrogen atom which is with a negative charge and located at 4.85 +/- 0.1 A, considered to be responsible for the nicotine-like activity. In cytisine the nitrogen atom in ring C appears at 4.8-9 A from the oxygen atom of the pyridine group and is also negatively charged.
The prolonged clinical and toxicological studies in many countries all over the world have proved the enormous harm of smoking on all organs and systems of the human organism. The danger of cardiovascular incidents (myocardial infarction, stenocardia, peripheral vascular diseases), diseases of the respiratory system (lung cancer, tracheobronchitis, etc.), as well as psychic and physiological dependence of addictive type is mostly emphasized.
Fig. 2 Stereoisomeric formulae of cytisine and nicotine (after Barlow, R.B. and McLeod, L.J.)
The treatment of nicotine addiction is a complex process in which drug therapy occupies an important part. Sopharma produces the drug Tabex, developed on the basis of the alkaloid Cytisine, which has an action similar to that of nicotine.
Pharmacodynamics of Cytisine
Cytisine is an agonist of the cholinoreceptors in the vegetative ganglia and belongs to the group of the gangliostimulating drugs. It excites the nicotine-sensitive cholinoreceptors of the postsynaptic membranes in the vegetative ganglia, chromaffin cells in the molecular part of the suprarenal gland and sinocarotid reflexogenic zone, which results in excitation of the respiratory center, predominantly through the reflexes, simulation of adrenaline release by the medullar part of the suprarenal glands and a rise in the blood pressure. After its absorption in the gastrointestinal tract, cytisine plays the part of a nicotine-substitute substance which decreases the period of interaction between nicotine and the corresponding receptors. This in turn leads to a gradual decrease and interruption of the smokers' psychic and physical nicotine dependence.
Many researchers confirm in different pharmacological experiments the similarity between the pharmacological properties of cytisine and nicotine, as described by Dale & Laidlaw (1912) and confirmed also by the conclusions of Zachowsky (1937), Anichkov (1937), Dobrev and Paskov (1953), Daleva (1963), etc., in whose opinion cytisine is more potent as a gangliostimulating than as a ganglioblocking agent.
Fig. 3 Mechanism of action of cytisine. Creation of the vicious cycle of tobacco addiction and the way to exit from it by means of Tabex
This similarity between the peripheral effects of cytisine and nicotine is more quantitative than qualitative. Comparable effects of both drugs have been obtained in experiments on cats and rats (studies on the blood pressure), or on guinea-pig ileum and rat diaphragm, the doses of cytisine being 1/4 to 2/3 from the nicotine dose.
As regards the effects on the central nervous system, Cytisine has a weaker effect on the respiration of anesthetized rabbits, compared to the effects on the peripheral nervous system.
Toxicity of Cytisine
Tabex was experimentally studied for its toxicological action on different kinds of experimental animals. The acute LD50 toxicity, the subchronic (30 days) and the chronic (80-180 days) toxicity were determined. The acute toxicity was determined on line H albino mice (intravenously, subcutaneously and orally); rats (intraperitoneally, subcutaneously and orally); dogs (subcutaneously and orally).
On the basis of the toxicological studies we can make the following conclusions:
Cytisine therapeutic range and tolerance
The therapeutic range of cytisine is much greater than of nicotine.
The daily therapeutic saturating doses of Tabex is 1.5 to 9 mg. The pharmacodynamic results obtained by Barlow et al. show that when applied at much higher concentrations in comparison with those of nicotine, Cytisine causes parasympathetic block of N-cholinergic receptors. Thus, for instance, the upper cervical ganglion of cat is blocked with 1.17+/-0.07 against 100 nmol for nicotine.
Tabex is very well tolerated, it does not provoke anorexia, nausea and vomiting in therapeutic doses. When applied according to appropriate schedule, it enables smokers to give up smoking gradually, without developing abstinence symptoms.
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