Antidepressant Drugs – Detailed Classification (INC B.Sc. Nursing Level)

Antidepressant drugs are classified based on their mechanism of action and effect on neurotransmitters such as serotonin, norepinephrine, and dopamine in the brain.

The major classes include:

1. Selective Serotonin Reuptake Inhibitors (SSRIs)

2. Tricyclic Antidepressants (TCAs)

3. Monoamine Oxidase Inhibitors (MAOIs)

4. Serotonin–Norepinephrine Reuptake Inhibitors (SNRIs)

5. Atypical Antidepressants

1. Selective Serotonin Reuptake Inhibitors (SSRIs)

Introduction

SSRIs are the most commonly prescribed antidepressants because they are effective and safer compared to older antidepressants.

They primarily increase the level of serotonin, a neurotransmitter responsible for mood regulation, sleep, and emotional stability.

Examples

Drug	Common Use
Fluoxetine	Depression, OCD
Sertraline	Depression, PTSD
Paroxetine	Anxiety disorders
Citalopram	Depression
Escitalopram	Depression, anxiety

Mechanism of Action

Normally, serotonin released from neurons is reabsorbed back into the nerve cell (reuptake).

SSRIs work by:

1. Blocking serotonin reuptake transporter (SERT)

2. Preventing reabsorption of serotonin

3. Increasing serotonin concentration in synaptic cleft

4. Improving mood and emotional balance

Therapeutic Uses

• Major depressive disorder

• Anxiety disorders

• Panic disorder

• Obsessive–compulsive disorder (OCD)

• Post-traumatic stress disorder (PTSD)

• Premenstrual dysphoric disorder

Common Side Effects

• Nausea

• Headache

• Insomnia

• Sexual dysfunction

• Weight changes

Important Nursing Points

• First-line treatment for depression

• Therapeutic effect occurs after 2–4 weeks

• Monitor suicidal thoughts during initial therapy

• Avoid combining with MAO inhibitors

2. Tricyclic Antidepressants (TCAs)

Introduction

TCAs are older antidepressants that were widely used before SSRIs.

They are effective but have more side effects, so they are usually used when SSRIs fail.

The name “tricyclic” refers to their three-ring chemical structure.

Examples

Drug	Common Use
Amitriptyline	Depression, neuropathic pain
Imipramine	Depression, enuresis
Nortriptyline	Depression
Clomipramine	OCD

Mechanism of Action

TCAs increase levels of serotonin and norepinephrine by blocking their reuptake.

Stepwise mechanism:

1. Block serotonin transporter

2. Block norepinephrine transporter

3. Increase neurotransmitter concentration

4. Improve mood and emotional state

However, TCAs also block other receptors, causing side effects.

Therapeutic Uses

• Major depression

• Chronic pain

• Migraine prevention

• Obsessive–compulsive disorder

• Nocturnal enuresis in children

Common Side Effects

• Dry mouth

• Constipation

• Blurred vision

• Urinary retention

• Drowsiness

These are called anticholinergic effects.

Serious Side Effects

• Cardiac arrhythmias

• Hypotension

• Seizures

Important Nursing Points

• Monitor ECG in cardiac patients

• Avoid overdose (high toxicity risk)

• Use cautiously in elderly patients

3. Monoamine Oxidase Inhibitors (MAOIs)

Introduction

MAO inhibitors are one of the oldest antidepressant drugs.

They work by blocking the enzyme monoamine oxidase, which normally breaks down neurotransmitters.

Because of serious food and drug interactions, they are used less frequently today.

Examples

Drug	Use
Phenelzine	Depression
Tranylcypromine	Depression
Isocarboxazid	Depression

Mechanism of Action

Monoamine oxidase enzyme normally breaks down:

• Serotonin

• Norepinephrine

• Dopamine

MAOIs work by:

1. Inhibiting monoamine oxidase enzyme

2. Preventing neurotransmitter breakdown

3. Increasing levels of serotonin, dopamine, and norepinephrine

Therapeutic Uses

• Severe depression

• Atypical depression

• Anxiety disorders

• Panic disorder

Major Side Effects

• Hypotension

• Weight gain

• Insomnia

• Headache

Serious Risk

Hypertensive Crisis

Occurs when patients eat tyramine-rich foods.

Foods to avoid:

• Cheese

• Wine

• Beer

• Processed meats

• Pickles

Symptoms include:

• Severe headache

• High blood pressure

• Sweating

• Palpitations

Nursing Responsibilities

• Educate patient about dietary restrictions

• Monitor blood pressure

• Avoid combining with SSRIs

4. Serotonin–Norepinephrine Reuptake Inhibitors (SNRIs)

Introduction

SNRIs are newer antidepressants that affect both serotonin and norepinephrine neurotransmitters.

They are effective for depression and chronic pain disorders.

Examples

Drug	Use
Venlafaxine	Depression
Duloxetine	Depression, neuropathic pain
Desvenlafaxine	Depression

Mechanism of Action

SNRIs work by:

1. Blocking serotonin reuptake

2. Blocking norepinephrine reuptake

3. Increasing neurotransmitter levels

4. Improving mood and energy levels

Therapeutic Uses

• Major depressive disorder

• Anxiety disorders

• Neuropathic pain•

Fibromyalgia

Side Effects

• Nausea

• Insomnia

• Increased blood pressure

• Headache

Nursing Points

• Monitor blood pressure regularly

• Useful in depression with chronic pain

5. Atypical Antidepressants

Introduction

Atypical antidepressants include drugs with unique mechanisms of action that do not fit into other classes.

They are often used when other antidepressants are not effective.

Examples

Drug	Mechanism
Bupropion	Dopamine & norepinephrine reuptake inhibitor
Mirtazapine	Enhances norepinephrine & serotonin release
Trazodone	Serotonin antagonist and reuptake inhibitor

Therapeutic Uses

• Depression

• Smoking cessation (bupropion)

• Sleep disorders

• Anxiety disorders

Side Effects

• Drowsiness

• Dry mouth

• Weight gain

• Dizziness

Nursing Points

• Bupropion may cause seizures in high doses

• Trazodone commonly used for insomnia

Comparison of Antidepressant Classes

Class	Main Neurotransmitter	Example
SSRIs	Serotonin	Fluoxetine
TCAs	Serotonin + Norepinephrine	Amitriptyline
MAOIs	Prevent breakdown of monoamines	Phenelzine
SNRIs	Serotonin + Norepinephrine	Venlafaxine
Atypical	Mixed mechanisms	Bupropion

Exam Tips (Very Important)

Students should remember:

Most asked questions

1. Classification of antidepressants

2. Mechanism of SSRIs

3. Side effects of TCAs

4. Dietary restriction with MAOIs

5. Nursing responsibilities during antidepressant therapy

Easy Memory Trick

Mnemonic for Antidepressant Classes

“SMART Drugs”

S → SSRIs

M → MAO inhibitors

A → Atypical antidepressants

R → Reuptake inhibitors (SNRIs)

T → Tricyclic antidepressants

60-Second Revision Card

Antidepressant Drug Classes

1️⃣ SSRIs → Increase serotoninExample: Fluoxetine

2️⃣ TCAs → Block serotonin & norepinephrine reuptakeExample: Amitriptyline

3️⃣ MAOIs → Prevent neurotransmitter breakdownExample: Phenelzine

4️⃣ SNRIs → Increase serotonin & norepinephrineExample: Venlafaxine

5️⃣ Atypical → Different mechanismsExample: Bupropion

Important Points

• SSRIs = first-line drugs

• TCAs = more side effects

• MAOIs require diet restriction

• Therapeutic effect takes 2–4 weeks