1. Classification of drugs used as antidepressants. 

• Tricyclic antidepressants(TADs)

There different kind of drugs listed under this group and differ with the type of amine they have in their structure. Amitriptyline(has a tertiary amine), Clomipramine(has a tertiary amine), Dosulepin(Dothiepin), Imipramine (a prototype and has a tertiary amine), Desimipramine (has a secondary amine), Trimipramine (Tertiary amine). These are called "tricyclic" because they all have a iminodibenzyl (tricyclic) core.

• Selective serotonin reuptake inhibitors (SSRIs)

The primary action of these antidepressant is the inhibition of the serotonin transporter(SERT). These include Citalopram, Escitalopram, Fluoxetine, Fluvoxamine, Paroxetine and Sertraline. 

• Monoamine oxidase A inhibitor

These are antidepressants whose primary function is to inhibit the MAO A, and they are known as follows; Moclobemide and Selegiline. 

• MAO inhibitors(non selective)

These block either MAO A or B and is not selective. These are Phenelzine and Tranylcypromine.

• Unicyclic and tetracyclic antidepressants

These do not fit in the other groups and are named due to their chemical structure.  The unicyclic antidepressants include Bupropion and the tetracyclic antidepressants include Mianserin, Maprotiline, Mirtazepine. 

• 5-HT modulators 

These are also known as selective serotonin-norepinephrine reuptake inhibitors and include the following Nefazodone, Trazodone, Vortioxetine, Duloxetine, Venlafaxine and Reboxetine.

• The last antidepressant does not fall under any of these groups and it is Agomelatine, it also has different mechanism of action from the others.

2. What do the existing drugs all have in common regarding their mechanisms of action?

Most of them block NET and SERT, inhibit 5-HT2a receptors, block MAO-A and MAO-B and are antagonists on some 5-HT receptors respectively. 

3. How long does it take for the anti-depressive effects of these drugs to appear? What is the reason for this?

 

4. How do the TADs and the selective serotonin reuptake inhibitors (SSRI’s) differ in respect of:

a) efficacy

SSRIs are more effective for major depressive disorders and anxiety disorders and are the first line treatment drug while TADs are less effective, treat only major depression and are seen as second or third line treatment drugs especial in treatment resistant depression.

b) side effects

SSRIs have serotonergic effect such as nausea, diarrhea and other GIT symptoms, has sexual effects such as loss of libido, delayed orgasm and diminished arousal. It may also cause post birth complications such as pulmonary hypertension. 

TADs on the other hand are normally associated with anticholinergic effects such as dry mouth, confusion, urinary retention, constipation and blurred vision. May have orthostatic hypotension and weight gain and in some cases sedation.

c) safety?

SSRIs are deemed safe in overdose while TADs symptoms such as increase in blood pressure, anticholinergic effects such as altered mental state and seizures can be observed during an overdose or in the administration of the drug in high dose.

5. What is the action of mirtazapine?

It is tetracyclic antidepressant and a noradrenergic and a specific 5-HTerfic agent (NaSSA).  It blocks a2 receptors, 5-HT2a receptors, 5-HT3 receptors and H1 and a2 receptors. And it indirectly stimulates 5-HT1a receptors.

6. What is the action of venlafaxine?

It is a 5-HT and noradrenergic reuptake inhibitor(SNRIs), moderately selectively blocks NET and SERT and is more potent for 5-HT than for NA.

7. What is the action of agomelatine?

It is a melatonin 1 and melatonin 2 receptor agonist and also a 5-HTC antagonist with antidepressant properties.