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:
See also: Pharmacology of antidepressants.
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. However, aside from mirtazapine, they do inhibit the reuptake of norepinephrine. TeCAs block the serotonin 5-HT2 receptors similarly to TCAs. Besides mirtazapine, they also block the α1-adrenergic receptor. 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. TeCAs block the histamine H1 receptor similarly to the TCAs, but tend to be even stronger antihistamines than TCAs. 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. Mianserin and mirtazapine are far less toxic than TCAs in overdose.[1] [2]
The binding profiles of various TeCAs in terms of their affinities for various receptors and transporters are as follows:[3]
| 58 | 16 | 4,310 | 0.5 | 2.0 | 6.0–50 | 41 | 50 | 2,600 | 3.6–160 | 7.9–25 | 1,000 | ||||||
| 5,800 | 11–12 | 1,000 | 51 | 122 | ND | 50 | 90 | 9,400 | 350–665 | 0.79–2.0 | 776 | 570 | |||||
| 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 | ||
| >10,000 | ≥4,600 | >10,000 | ≥3,330 | 6.3–69 | 200 | 8.9–39 | 7.9 | 265 | 316–1,815 | 18–88 | >5,454 | 0.14–1.6 | >10,000 | 670 | |||
| >10,000 | 220 | >10,000 | 24 | ||||||||||||||
| Values are . 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.