Tetracyclic antidepressants (TeCAs) are a class of antidepressants that were first introduced in the 1970s. They are named after their tetracyclic chemical structure, containing four rings of atoms, and are closely related to the tricyclic antidepressants (TCAs), which contain three rings of atoms.
Drugs that contain four rings not all fused together but are sometimes still classified as TeCAs include:
Drugs that contain four rings not all fused together but could still be classified as tetracyclic include:
Drugs that contain four rings not all fused together but could still be classified as tetracyclic include:
TeCAs have diverse pharmacology and differ from TCAs in a number of ways. With the exception of amoxapine, TeCAs do not inhibit the reuptake of serotonin [ citation needed ]. However, aside from mirtazapine, they do inhibit the reuptake of norepinephrine [ citation needed ]. TeCAs block the serotonin 5-HT2 receptors similarly to TCAs. Besides mirtazapine, they also block the α1-adrenergic receptor [ citation needed ]. Conversely, whereas TCAs have relatively low affinity for the α2-adrenergic receptor, mianserin and mirtazapine potently antagonize this receptor, and this action is thought to be involved in their antidepressant effects[ citation needed ]. TeCAs block the histamine H1 receptor similarly to the TCAs, but tend to be even stronger antihistamines than TCAs[ citation needed ]. On the other hand, in contrast to almost all TCAs, TeCAs have only low affinity for the muscarinic acetylcholine receptors, and for this reason, are associated with few or no anticholinergic side effects [ citation needed ]. Mianserin and mirtazapine are far less toxic than TCAs in overdose. [1] [2]
The binding profiles of various TeCAs in terms of their affinities (Ki, nM) for various receptors and transporters are as follows: [3]
| Compound | SERT | NET | DAT | 5-HT1A | 5-HT2A | 5-HT2B | 5-HT2C | 5-HT3 | 5-HT6 | 5-HT7 | α1 | α2 | D2 | H1 | H2 | mACh |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Amoxapine | 58 | 16 | 4,310 | ND | 0.5 | ND | 2.0 | ND | 6.0–50 | 41 | 50 | 2,600 | 3.6–160 | 7.9–25 | ND | 1,000 |
| Maprotiline | 5,800 | 11–12 | 1,000 | ND | 51 | ND | 122 | ND | ND | 50 | 90 | 9,400 | 350–665 | 0.79–2.0 | 776 | 570 |
| Mianserin | 4,000 | 71 | 9,400 | 400–2,600 | 1.6–20 | 1.6–55 | 0.63–6.5 | 5.8–300 | 55–81 | 48–56 | 34 | 3.8–73 | ≥2,100 | 0.30–1.7 | 437 | 820 |
| Mirtazapine | >10,000 | ≥4,600 | >10,000 | ≥3,330 | 6.3–69 | 200 | 8.9–39 | 7.9 | ND | 265 | 316–1,815 | 18–88 | >5,454 | 0.14–1.6 | >10,000 | 670 |
| Setiptiline | >10,000 | 220 | >10,000 | ND | ND | ND | ND | ND | ND | ND | ND | 24 | ND | ND | ND | ND |
| Values are Ki (nM). The smaller the value, the more strongly the drug binds to the site. For assay species and references, see the individual drug articles. Most but not all values are for human proteins. | ||||||||||||||||
The TeCAs act as antagonists or inverse agonists of the receptors and as inhibitors of the transporters.
Tricyclic antidepressants (TCAs) are a class of medications that are used primarily as antidepressants. TCAs were discovered in the early 1950s and were marketed later in the decade. They are named after their chemical structure, which contains three rings of atoms. Tetracyclic antidepressants (TeCAs), which contain four rings of atoms, are a closely related group of antidepressant compounds.
Maprotiline, sold under the brand name Ludiomil among others, is a tetracyclic antidepressant (TeCA) that is used in the treatment of depression. It may alternatively be classified as a tricyclic antidepressant (TCA), specifically a secondary amine. In terms of its chemistry and pharmacology, maprotiline is closely related to such-other secondary-amine TCAs as nortriptyline and protriptyline and has similar effects to them, albeit with more distinct anxiolytic effects. Additionally, whereas protriptyline tends to be somewhat more stimulating and in any case is distinctly more-or-less non-sedating, mild degrees of sedation may be experienced with maprotiline.
Mirtazapine, sold under the brand name Remeron among others, is an atypical tetracyclic antidepressant, and as such is used primarily to treat depression. Its effects may take up to four weeks, but can also manifest as early as one to two weeks. It is often used in cases of depression complicated by anxiety or insomnia. The effectiveness of mirtazapine is comparable to other commonly prescribed antidepressants. It is taken by mouth.
Serotonin–norepinephrine reuptake inhibitors (SNRIs) are a class of antidepressant medications used to treat major depressive disorder (MDD), anxiety disorders, social phobia, chronic neuropathic pain, fibromyalgia syndrome (FMS), and menopausal symptoms. Off-label uses include treatments for attention-deficit hyperactivity disorder (ADHD), obsessive–compulsive disorder (OCD), and migraine prevention. SNRIs are monoamine reuptake inhibitors; specifically, they inhibit the reuptake of serotonin and norepinephrine. These neurotransmitters are thought to play an important role in mood regulation. SNRIs can be contrasted with the selective serotonin reuptake inhibitors (SSRIs) and norepinephrine reuptake inhibitors (NRIs), which act upon single neurotransmitters.
Amoxapine, sold under the brand name Asendin among others, is a tricyclic antidepressant (TCA). It is the N-demethylated metabolite of loxapine. Amoxapine first received marketing approval in the United States in 1980, approximately 10 to 20 years after most of the other TCAs were introduced in the United States.
Imipramine, sold under the brand name Tofranil, among others, is a tricyclic antidepressant (TCA) mainly used in the treatment of depression. It is also effective in treating anxiety and panic disorder. Imipramine is taken by mouth.
Noradrenergic and specific serotonergic antidepressants (NaSSAs) are a class of psychiatric drugs used primarily as antidepressants. They act by antagonizing the α2-adrenergic receptor and certain serotonin receptors such as 5-HT2A and 5-HT2C, but also 5-HT3, 5-HT6, and/or 5-HT7 in some cases. By blocking α2-adrenergic autoreceptors and heteroreceptors, NaSSAs enhance adrenergic and serotonergic neurotransmission in the brain involved in mood regulation, notably 5-HT1A-mediated transmission. In addition, due to their blockade of certain serotonin receptors, serotonergic neurotransmission is not facilitated in unwanted areas, which prevents the incidence of many side effects often associated with selective serotonin reuptake inhibitor (SSRI) antidepressants; hence, in part, the "specific serotonergic" label of NaSSAs.
Trimipramine, sold under the brand name Surmontil among others, is a tricyclic antidepressant (TCA) which is used to treat depression. It has also been used for its sedative, anxiolytic, and weak antipsychotic effects in the treatment of insomnia, anxiety disorders, and psychosis, respectively. The drug is described as an atypical or "second-generation" TCA because, unlike other TCAs, it seems to be a fairly weak monoamine reuptake inhibitor. Similarly to other TCAs, however, trimipramine does have antihistamine, antiserotonergic, antiadrenergic, antidopaminergic, and anticholinergic activities.
Dosulepin, also known as dothiepin and sold under the brand name Prothiaden among others, is a tricyclic antidepressant (TCA) which is used in the treatment of depression. Dosulepin was once the most frequently prescribed antidepressant in the United Kingdom, but it is no longer widely used due to its relatively high toxicity in overdose without therapeutic advantages over other TCAs. It acts as a serotonin–norepinephrine reuptake inhibitor (SNRI) and also has other activities including antihistamine, antiadrenergic, antiserotonergic, anticholinergic, and sodium channel-blocking effects.
Mianserin, sold under the brand name Tolvon among others, is an atypical antidepressant that is used primarily in the treatment of depression in Europe and elsewhere in the world. It is a tetracyclic antidepressant (TeCA). Mianserin is closely related to mirtazapine, both chemically and in terms of its actions and effects, although there are significant differences between the two drugs.
The second-generation antidepressants are a class of antidepressants characterized primarily by the era of their introduction, approximately coinciding with the 1970s and 1980s, rather than by their chemical structure or by their pharmacological effect. As a consequence, there is some controversy over which treatments actually belong in this class.
Butriptyline, sold under the brand name Evadyne among others, is a tricyclic antidepressant (TCA) that has been used in the United Kingdom and several other European countries for the treatment of depression but appears to no longer be marketed. Along with trimipramine, iprindole, and amoxapine, it has been described as an "atypical" or "second-generation" TCA due to its relatively late introduction and atypical pharmacology. It was very little-used compared to other TCAs, with the number of prescriptions dispensed only in the thousands.
Iprindole, sold under the brand names Prondol, Galatur, and Tertran, is an atypical tricyclic antidepressant (TCA) that has been used in the United Kingdom and Ireland for the treatment of depression but appears to no longer be marketed. It was developed by Wyeth and was marketed in 1967. The drug has been described by some as the first "second-generation" antidepressant to be introduced. However, it was very little-used compared to other TCAs, with the number of prescriptions dispensed only in the thousands.
Setiptiline, also known as teciptiline, is a tetracyclic antidepressant (TeCA) that acts as a noradrenergic and specific serotonergic antidepressant (NaSSA). It was launched in 1989 for the treatment of depression in Japan by Mochida.
Oxaprotiline, also known as hydroxymaprotiline, is a norepinephrine reuptake inhibitor belonging to the tetracyclic antidepressant (TeCA) family and is related to maprotiline. Though investigated as an antidepressant, it was never marketed.
Ciclazindol (WY-23409) is an antidepressant and anorectic drug of the tetracyclic chemical class that was developed in the mid to late 1970s, but was never marketed. It acts as a norepinephrine reuptake inhibitor, and to a lesser extent as a dopamine reuptake inhibitor. Ciclazindol has no effects on the SERT, 5-HT receptors, mACh receptors, or α-adrenergic receptors, and has only weak affinity for the H1 receptor. As suggested by its local anesthetic properties, ciclazindol may also inhibit sodium channels. It is known to block potassium channels as well.
Quinupramine is a tricyclic antidepressant (TCA) used in Europe for the treatment of depression.
Tetracyclics are cyclic chemical compounds that contain four fused rings of atoms, for example, Tröger's base.
Aptazapine (developmental code name CGS-7525A) is a tetracyclic antidepressant (TeCA) that was assayed in clinical trials for the treatment of depression in the 1980s but was never marketed. It is a potent α2-adrenergic receptor antagonist with ~10× the strength of the related compound mianserin and has also been shown to act as a 5-HT2 receptor antagonist and H1 receptor inverse agonist, while having no significant effects on the reuptake of serotonin or norepinephrine. Based on its pharmacological profile, aptazapine may be classified as a noradrenergic and specific serotonergic antidepressant (NaSSA).