"
Biogenic Amine Theory of Depression
The Biogenic Amine Theory suggests that depression is linked to a deficiency in certain neurotransmitters, including serotonin (5-HT), norepinephrine (NE), and dopamine (DA). When these neurotransmitters are deficient, it results in symptoms of depression. Antidepressants work by increasing the levels of these neurotransmitters in the brain.
Classification of Antidepressants
Antidepressants are classified into several categories based on their mechanism of action. These include:
- Selective Serotonin Reuptake Inhibitors (SSRIs)
- Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)
- Tricyclic Antidepressants (TCAs)
- Monoamine Oxidase Inhibitors (MAOIs)
- Atypical Antidepressants
1. Selective Serotonin Reuptake Inhibitors (SSRIs)
- Mechanism: Inhibit the reuptake of serotonin into presynaptic neurons, increasing serotonin levels in the synaptic cleft.
- Examples: Fluoxetine, Sertraline, Citalopram, Escitalopram.
- Therapeutic Uses: Major depressive disorder, anxiety disorders, OCD, panic disorder.
- Adverse Effects: Nausea, insomnia, sexual dysfunction, weight gain, agitation.
- Contraindications: Hypersensitivity to SSRIs, concurrent use with MAOIs.
2. Serotonin-Norepinephrine Reuptake Inhibitors (SNRIs)
- Mechanism: Block the reuptake of both serotonin and norepinephrine, increasing the concentrations of these neurotransmitters in the brain.
- Examples: Venlafaxine, Duloxetine, Desvenlafaxine.
- Therapeutic Uses: Major depressive disorder, generalized anxiety disorder, diabetic neuropathy, fibromyalgia.
- Adverse Effects: Nausea, dizziness, sexual dysfunction, insomnia, hypertension (especially at higher doses).
- Contraindications: Hypersensitivity to SNRIs, concurrent use with MAOIs.
3. Tricyclic Antidepressants (TCAs)
- Mechanism: Inhibit the reuptake of serotonin and norepinephrine and block various receptors (histamine, acetylcholine), contributing to therapeutic and side effects.
- Examples: Amitriptyline, Nortriptyline, Imipramine.
- Therapeutic Uses: Major depressive disorder, neuropathic pain, chronic pain, enuresis.
- Adverse Effects: Anticholinergic effects (dry mouth, constipation), sedation, weight gain, sexual dysfunction, cardiovascular effects (tachycardia, hypotension).
- Contraindications: Recent myocardial infarction, angle-closure glaucoma, concurrent use with MAOIs.
4. Monoamine Oxidase Inhibitors (MAOIs)
- Mechanism: Inhibit monoamine oxidase, the enzyme responsible for breaking down serotonin, norepinephrine, and dopamine, increasing their levels in the brain.
- Examples: Phenelzine, Tranylcypromine, Isocarboxazid.
- Therapeutic Uses: Major depressive disorder, atypical depression, panic disorder.
- Adverse Effects: Orthostatic hypotension, weight gain, sexual dysfunction, insomnia, hypertensive crisis (especially with dietary tyramine).
- Contraindications: Concurrent use with SSRIs, SNRIs, tricyclic antidepressants, foods high in tyramine.
5. Atypical Antidepressants
- Mechanism: Various mechanisms including blocking reuptake of serotonin, norepinephrine, or dopamine, or modulating specific receptor sites.
- Examples: Bupropion, Mirtazapine, Trazodone.
- Therapeutic Uses: Major depressive disorder, smoking cessation (Bupropion), insomnia (Trazodone), anxiety (Mirtazapine).
- Adverse Effects: Bupropion – insomnia, dry mouth, weight loss, seizures (at high doses); Mirtazapine – sedation, weight gain, increased appetite; Trazodone – sedation, priapism.
- Contraindications: Bupropion – history of seizures, eating disorders; Trazodone – concurrent use with MAOIs.
