ISBN : 978-93-85073-24-3 Antidepressants are usually classified according to structure [e.g., tricyclic antidepressants (TCAs)] or function [e.g., monoamine oxidase inhibitors (MAOIs), selective serotonin reuptake inhibitors (SSRIs)]. However, it may be more useful to classify them according to the acute pharmacologic effects that are presumed to trigger behavioral improvement. If this is done, the antidepressants can be grouped in four categories (Table 1.1). First are the drugs that selectively block the reuptake of norepinephrine (NE). These include certain TCAs and TCA-like compounds (maprotiline). Another drug that falls into this category is reboxetine, although it is distinct structurally from the TCAs and TCA like compounds [112]. Second are the SSRIs, which, as their class name implies, selectively block the reuptake of serotonin [5-hydroxytryptimine (5-HT)] in-vivo. Third are the drugs that act nonselectively on noradrenergic and serotoninergic neurons with a resultant enhancement of synaptic transmission. Some TCAs are in this category, as are the MAOIs. Some novel drugs are also in this category [113]. Table 1.1: MECHANISM-BASED CLASSIFICATION FOR ANTIDEPRESSANTS Category Mechanism I Selective blockade of NE reuptake (SNRIs) II Selective blockade of 5- HT reuptake (SSRIs) Nonselective III enhancement of NE and 5-HT transmission Unknown potent IV stimulatory effects on NE or 5-HT Examples DMI, NT amoxapine, maprotiline reboxetine Citalopram, fluoxetine, paroxetine, sertraline IMI, AMI phenelzine, tranylcypromine venlafaxine, mirtazapine Trimipramine, bupropion, nefazodone, trazodone TCA Current Classification (If Any) TCAs , TCA-like SSRIs TCAs, MAOIs (sometimes with SSRIs) 6
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