Antidepressants inhibitors

As a consequence, several drugs have been developed by enhancing the side effect of another drug. For example, the mood-improving effect of iproniazid was discovered when it was tested as an antituberculous drug antidepressant inhibitors of neurotransmitter reuptake, like imipramine and desipramine, stem from the antipsychotic dopamine antagonist chlorpromazine, which itself was derived from Hi antihistaminics [35,36,51]. 

Patients receiving monoamine oxidase inhibitors (MAOI) as antidepressant therapy have been especially subject to the hypertensive effects of vasoactive amines (52). These dietary amines have also been impHcated as causative agents ia migraine. Other aaturaHy occurring alkaloids (qv) have been recognized for centuries as possessing neurological stimulant and depressant properties. 

In addition to halopeiidol, the putative neuroleptics, limcazole (311), lemoxipiide (312), and gevotioline (313) bind to (7-ieceptois as does the dopamine uptake blocker, GBR 12909 (314) and two ligands active at the NMDA receptor, ifenprodil (315) and CNS 1102 (316). NPC 16377, (317) is a selective (7-teceptor ligand. MAO inhibitors and antidepressants also bind to (7-teceptors. Some evidence indicates that (7-teceptors in the brain are in fact a form of cytochrome which may account for the diversity of ligands interacting with (7-sites. 

SSRIs are well tolerated. Adverse effects for compounds in this class include nervousness, tremor, dizziness, headache, insomnia, sexual dysfunction, nausea, and diarrhea. In addition, the tricycHc antidepressant clomipramine (33), which is a potent nonselective serotonin reuptake inhibitor, is approved for treatment of obsessive—compulsive disorder. 

Treatment of Major Depression. Dmgs commonly used for the treatment of depressive disorders can be classified heuristicaHy iato two main categories first-generation antidepressants with the tricycHc antidepressants (TCAs) and the irreversible, nonselective monoamine—oxidase (MAO) inhibitors, and second-generation antidepressants with the atypical antidepressants, the reversible inhibitors of monoamine—oxidase A (RIMAs), and the selective serotonin reuptake inhibitors (SSRIs). Table 4 fists the available antidepressants. 

Monoamine—Oxidase Inhibitors. In the mid-1950s, tuberculosis patients with depression being treated with iproniazid (42) were occasionally reported to become euphoric. This observation led to the discovery of irreversible monoamine—oxidase (MAO) inhibiting properties. Hydrazine and nonhydrazine-related MAO inhibitors were subsequentiy shown to be antidepressants (122). Three other clinically effective irreversible MAO inhibitors have been approved for treatment of major depression phenelzine (43), isocarboxazid (44), and tranylcypromine (45). 

SSRIs are widely used for treatment of depression, as well as, for example, panic disorders and obsessive—compulsive disorder. These dmgs are well recognized as clinically effective antidepressants having an improved side-effect profile as compared to the TCAs and irreversible MAO inhibitors. Indeed, these dmgs lack the anticholinergic, cardiovascular, and sedative effects characteristic of TCAs. Their main adverse effects include nervousness /anxiety, nausea, diarrhea or constipation, insomnia, tremor, dizziness, headache, and sexual dysfunction. The most commonly prescribed SSRIs for depression are fluoxetine (31), fluvoxamine (32), sertraline (52), citalopram (53), and paroxetine (54). SSRIs together represent about one-fifth of total worldwide antidepressant unit sales. 

Reversible Inhibitors of Monoamine Oxidase. Selective MAO-A inhibitors, which aie leveisible (so-called RIMAs), have also been developed, theiefoie substantially leduciag the potential foi food and dmg iateiactions. Indeed, the tyiamine-potentiating effects of these dmgs is much reduced compared with the irreversible MAO inhibitors. The RIMAs represent effective and safer alternatives to the older MAO inhibitors. The only marketed RIMAs ate toloxatone [29218-27-7] and moclobemide (55). The latter is used widely as an effective, weU-tolerated antidepressant. 

The second-generation antidepressants, particularly RIMAs and SSRJs, are much less toxic ia overdose than the older TCAs and irreversible MAO inhibitors. However, similar to first-generation antidepressants, the therapeutic effect only becomes manifest after several weeks. Up to one-third of depressed patients are nonresponders. Ideally, an antidepressant would combine a more rapid onset of action with greater clinical efficacy and a higher responder rate, as well as even better tolerability. 

Modulation of second-messenger pathways is also an attractive target upon which to base novel antidepressants. Rolipram [61413-54-5] an antidepressant in the preregistration phase, enhances the effects of noradrenaline though selective inhibition of central phosphodiesterase, an enzyme which degrades cycHc adenosiae monophosphate (cAMP). Modulation of the phosphatidyl iaositol second-messenger system coupled to, for example, 5-HT,, 5-HT,3, or 5-HT2( receptors might also lead to novel antidepressants, as well as to alternatives to lithium for treatment of mania. Novel compounds such as inhibitors of A-adenosyl-methionine or central catechol-0-methyltransferase also warrant attention. 

Selected for clinical trials as a compound to calm agitated patients, imipramine was relatively ineffective. However, it was observed to be effective in the treatment of certain depressed patients (38). Early studies on the mechanism of action showed that imipramine potentiates the effects of the catecholamines, primarily norepinephrine. This finding, along with other evidence, led to the hypothesis that the compound exerts its antidepressant effects by elevating norepinephrine levels at central adrenergic synapses. Subsequent studies have shown that the compound is a potent inhibitor of norepinephrine reuptake and, to a lesser extent, the uptake of serotonin, thus fitting the hypothesis that had been developed to explain the antidepressant actions ofMAOIs. 

Two recently introduced antidepressants are notable m that they are selective serotonin uptake inhibitors Citalopram (19) is reported to be as effective as amitriptyline m the treatment of endogenous depression [75, 16] Fluoxetine (20) as the hydrochlonde is approved for major depressive disorders mcludmg those with concomitant anxiety Interestmgly, it also appears useful m the treatment of obesity [17]... 

Almost anyone who has at some time in his life met some reverses is familiar with depression. In the normal course of events, changing circumstances will soon lead to the replacement of this state of mind by a more pleasant one. There exist, however, a set of pathologic states in which depression feeds on itself in a destructive cycle. Individuals affected with this syndrome— whether precipitated by outside events or not—eventually find it most difficult to function. The advent of antidepressant drugs, first the MAO inhibitors and more recently the tricyclic antidepressants, have made this syndrome amenable to treatment. 

Therapeutic Function Antidepressant monoamine oxidase inhibitor Chemical Name 4-Pyridinecarboxylic acid 2-(1-methylethyl)hydrazide Common Name —... 

Antidepressants are used in the treatment of neuropathic pain and headache. They include the classic tricyclic compounds and are divided into nonselective nor-adrenaline/5-HT reuptake inhibitors (e.g., amitriptyline, imipramine, clomipramine, venlafaxine), preferential noradrenaline reuptake inhibitors (e.g., desipramine, nortriptyline) and selective 5-HT reuptake inhibitors (e.g., citalopram, paroxetine, fluoxetine). The reuptake block leads to a stimulation of endogenous monoaminer-gic pain inhibition in the spinal cord and brain. In addition, tricyclics have NMDA receptor antagonist, endogenous opioid enhancing, Na+ channel blocking, and K+ channel opening effects which can suppress peripheral and central sensitization. Block of cardiac ion channels by tricyclics can lead to life-threatening arrhythmias. The selective 5-HT transporter inhibitors have a different side effect profile and are safer in cases of overdose [3]. 

Iproniazid was among the first psychotropic antidepressants to be discovered and introduced into the clinic. Although this inhibitor and others that followed... 

Non-selective monoamine reuptake inhibitors (NSMRI) are a group of antidepressants, which function by inhibiting the reuptake of noradrenaline... 

Noradrenaline transporters (NAT) are localized in the presynaptic plasma membrane of adrenergic nerve terminals. They belong to a family of proteins with 12 putative transmembrane proteins which are responsible for recycling of released neurotransmitters (noradrena-line/adrenaline, dopamine, serotonin, amino acid transmitters) back into the presynaptic nerve ending. Noradrenaline transporters can be blocked by a number of different antidepressant drags, including tricyclic antidepressants (e.g. desipramine) and selective noradrenaline reuptake inhibitors (e.g. reboxetine). 

Selective noradrenaline reuptake inhibitors (SNRIs) are a group of drugs, which act as antidepressants by the selective inhibition of the reuptake of noradrenaline from the synaptic cleft via the selective blockade of the noradrenaline-specific neurontransmitter transporter (e.g. reboxetine). 

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