How are antidepressant drugs defined [20%] How do you classify antidepressant drugs based on the mode of action [30%] Describe briefly the mechanism of action of the selective serotonin reuptake inhibitors (SSRIs) [50%]

What Are Antidepressant Drugs? Depression, a condition in which a person gets bad temperedand has strong feelings of disliking and hatred. This has an impact on his way of thinking, actions, behavior and infact his everyday routine. The symptoms of depression are sadness, anxiety, hopelessness, irritation etc Antidepressants drugs are psychiatric molecules that are given to patients having moderate or severe level of depression and some other conditions like anxiety disorders, eating disorders, chronic pain, obsessive compulsive disorder, neuropathic pain, snoring, substance abuse and certain sleep disorders. Antidepressants may not treat depression itself but are useful for decreasing the symptoms of depression. They balance the variation in neurotransmitters that have caused certain mood and behavioral changes. (Brigitta, 2002) (Mayoclinic.org, 2014)Classification of Anti-Depressant Drugs On The Basis Of Mode of Action:On the basis of mechanism of action, Anti-depressant drugs are divided into seven main categories. A brief description of their distinction in mode of action is also described along with their examples.TCAs: Tricyclic antidepressants block reuptake of nor-epinephrine and increases its level. Examples include amitryptyline, imipramine, clomipramine etcMAOIs: Monoamineoxidase inhibitors inhibits the enzymes monoamineoxidase that degrades norepinephrine, serotonin etc, thus increasing their levels. Examples include Tranylcypromine, Phenelzine etcSSRIs: Selective Serotonin reuptake inhibitors block reuptake of serotonin only. These include fluoxetine, fluvoxamine etcSNRIs: Serotonin norepinephrine reuptake inhibitors block uptake of both serotonin and norepinephrine. Example includes Venlafaxine.NARI: Noradrenalin reuptake inhibitors block reuptake of noradrenalin. Example includes Reboxetine.RIMA: Reversible Inhibitors of Monoamine Oxidase-A inhibits breakdown of three neurotransmitters i.e. dopamine, norepinephrine and serotonin. Example is Moclobemide.NaSSa: Noradrenergic and Specific Serotonergic Antidepressants increase concentration of noradrenalin and serotonin in synaptic cleft by inhibiting auto receptors. Example includes Mrtazapine (Rxpgonline.com, 2014)Mechanism of Action of Selective Serotonin Reuptake Inhibitor (SSRIs):Selective serotonin reuptake inhibitor works by blocking serotonin reuptake. Reuptake is a natural phenomenon in which different neurotransmitters are naturally reabsorbed back by nerve cells of brain. When a reuptake inhibitor like SSRI is used, it prevent the reabsorbtion of neurotransmitter as a result the level of neurotransmitter in the synaptic cleft increases, thus improving the communication between nerve cells and reinforcing those brain regions that are involved in mood regulation. (Webmd.com, 2014)It is also proposed that the main restorative outcome of SSRIs is observed in delayed neuro chemical adaptation. According to this proposal serotonin desensitize certain receptors in midbrain. These receptors are somatodendritic serotonin 1A auto receptors. When these become desensitize the level of serotonin in crucial areas of brain increases that may help combating different signs and symptoms of depression. (Stahl, 1998)These are different than TCAs as they only block reuptake of serotonin and not of nor-epinephrine and causes fewer side effects than TCAs. Still SSRIs show some side effects that include nausea, vomiting, dry mouth, headache, sweating, gastrointestinal discomfort etc and is given with caution in patients having suicidal tendencies. Examples of SSRI include fluoxetine, fluvoxamine, citalopram, sertraline, paroxetine etc (Thebrain.mcgill.ca, 2014)References:Brigitta, B. (2002). Pathophysiology of depression and mechanisms of treatment. Dialogues in clinical neuroscience, 4(1), p.7.Mayoclinic.org, (2014). Antidepressants: Selecting one thats right for you – Mayo Clinic. [online] Available at: http://www.mayoclinic.org/diseases-conditions/depression/in-depth/antidepressants/art-20046273 [Accessed 13 May. 2014].Rxpgonline.com, (2014). Classification of Antidepressant Drugs (Useful for MRCPsych ISQs) Psychiatry. [online] Available at: http://www.rxpgonline.com/article1425.html [Accessed 13 May. 2014].Stahl, S. (1998). Mechanism of action of serotonin selective reuptake inhibitors: serotonin receptors and pathways mediate therapeutic effects and side effects. Journal of affective disorders, 51(3), pp.215–235.Thebrain.mcgill.ca, (2014). THE BRAIN FROM TOP TO BOTTOM. [online] Available at: http://thebrain.mcgill.ca/flash/i/i_08/i_08_m/i_08_m_dep/i_08_m_dep_isrs.html [Accessed 13 May. 2014Webmd.com, (2014). How Antidepressants Work: SSRIs, MAOIs, Tricyclics, and More. [online] Available at: http://www.webmd.com/depression/how-different-antidepressants-work [Accessed 13 May. 2014].