The most frequently used drugs are tricyclic antidepressants, which received their name from the organization of their chemical structures, in particular the systems consisting of two benzene rings joined to a central 7-membered ring with a dialkylaminoalkyl group connected to the central ring. Depending on the substituents on the terminal nitrogen atom in the amine-containing side chain, they in turn are subdivided into tertiary (imipramine, amitriptyline, trimipramine, doxepin) and secondary (desipramine, nortriptyline, protripty-line) amines. These classifications are very formal and are not based on the most essential structural variations of the examined drugs; however, they are accepted in pharmacology.
Tricyclic antidepressants are chemically, pharmacologically, and toxicologically very similar to antipsychotics of the phenothiazine series. The mechanism of action of tricyclic depressants is not conclusively known, and not one of the proposed hypotheses is currently capable of fully explaining their antidepressant effect.
It is believed that tricyclic antidepressants inhibit the (neuronal) reuptake of norepinephrine (noradrenaline) and/or serotonin by presynaptic nerve endings, thus blocking one of the leading mechanisms of their inactivation, and thereby increasing the concentration of the indicated amines potentiating their effects. It should be noted that, as a rule, secondary amines, which are representatives of tricyclic antidepressants, exhibit high activity, blocking the neuronal reuptake of norepinephrine, while tertiary amines act more on the neuronal reuptake of serotonin.
It is also possible that tricyclic antidepressants block presynaptic a2 adrenoreceptors, thus increasing the quantity of releasable norepinephrine and/or serotonin. Tricyclic anti-depressants are used for relieving symptoms of depression (especially of the endogenous type), for controlling anxiety associated with depressive conditions, for treating depression in patients with maniac-depressive psychosis, and so on.
7.1.1 Tertiary amines—representatives of tricyclic antidepressants
Imipramine: Imipramine, 5-[3-(dimethylamino)propyl]-10,11-dihydro-5H-dibenz[b,f] azepine (7.1.1), is synthesized by the alkylation of 10,11-dihydro-5H-dibenz[b,f]azepine using 3-dimethylaminopropylchloride in the presence of sodium amide [1-3].
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