First antidepressant drugs were a casual finding and they affect to various neurotransmitters systems. Usually these old drugs produce many secondary effects. Afterwards, some hypotheses have emerged about the neurotransmission implicated in depression (monoamines: serotonin, noradrenalin and dopamine). Drug development progresses in parallel to this investigation so more selective drugs appeared as Selective Serotonin Reuptake Inhibitors, (from now on SSRIs), ameliorating secondary effects. Antidepressant classification depends on the assumption of their action mechanism. Following that schema, there are eight different pharmacological mechanisms at least. The most of the antidepressants block monoamine reuptake, but others block alpha-2 receptors or monoamineoxidase enzyme. 2.1 Monoamine reuptake inhibitors 2.1.1 Tricyclic and tetracyclic antidepressants (TCA) The tricyclic and tetracyclic branch of antidepressants has a demonstrated and high efficacy, only limited by their sedative and anticholinergic effects. They act on a huge number of receptors, and are cardiotoxic in case of overdoses, as anticholinergic toxicity and convulsions. Pharmacological actions: A significant part is absorbed totally after oral administration. They have a significant metabolism by first-pass. Maximum plasmatic concentration is reached in 2-48 hours but equilibrium appears after 5-7 days. Their long half-life allows them to be used once in a day. Clearance of tricyclics is dependent primarily on hepatic cytochrome P450 (CYP) oxidative enzymes. Effects on organs and special systems: Significant effects on the cardiovascular system appear at therapeutic dose: they are classified as anti-arrhythmic type IA, since they interrupt the ventricular fibrillation and can increase the collateral blood flow of ischemic heart. In overdose they are highly cardiotoxic and cause a decrease in contractility, increased irritability myocardial, hypotension and tachycardia. 2.1.2 Main therapeutic indications Depression: treatment of one major depressive episode and prophylaxis of one major depressive episode (main directions); depression in Bipolar type I disorder (in resistant cases, with many precautions to prevent swinging: associated with anticonvulsivants or lithium); one depressive episode with psychotic manifestations almost always requires the simultaneous administration of an antipsychotic drug and an antidepressant; Disorder mood due to a general medical disease with depressive features Panic disorder. Generalized anxiety disorder. Obsessive-compulsive disorder: clomipramin especially. None of the others seems so effective. Others: Alimentary conduct disorder and pain disorder.
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