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Atypical Antidepressant (Tetracyclic)

Mirtazapine | Remeron

Clinical Overview

Mirtazapine is an atypical tetracyclic antidepressant indicated for the treatment of major depressive disorder. It has a unique mechanism of action that combines antidepressant efficacy with beneficial effects on sleep and appetite, making it particularly valuable for patients with depression accompanied by insomnia, weight loss, or anxiety.

Primary Clinical Applications

Mirtazapine is indicated for major depressive disorder and is commonly used off-label for insomnia, anxiety disorders, PTSD, and appetite stimulation. It is particularly beneficial for elderly patients and those with comorbid sleep disturbances or weight loss.

Mechanism and Clinical Benefits

Mirtazapine blocks α2-adrenergic autoreceptors and heteroreceptors, increasing norepinephrine and serotonin release. It also blocks 5-HT2A, 5-HT2C, 5-HT3, and H1 receptors, contributing to its sedating effects and appetite stimulation while reducing sexual side effects and nausea.

Unique Advantages

Unlike SSRIs, mirtazapine typically causes weight gain and sedation, which can be therapeutic for appropriate patients. It has minimal sexual side effects and low risk of drug interactions, making it suitable for elderly patients or those on multiple medications.

Prescribing Information

Dosing & Administration

Major Depressive Disorder:

  • Initial: 15 mg daily at bedtime
  • Increase: May increase at 1-2 week intervals
  • Target range: 15-45 mg daily
  • Maximum: 45 mg daily

Elderly:

  • Initial: 7.5-15 mg daily at bedtime
  • Titrate slowly: Based on response and tolerability

Administration:

  • Preferably at bedtime due to sedating effects
  • Can be taken with or without food
  • SolTab formulation dissolves on tongue

Indications

  • Major depressive disorder
  • Off-label: Insomnia, anxiety, PTSD, appetite stimulation

Contraindications

  • MAOI use within 14 days
  • Known hypersensitivity to mirtazapine
  • Concurrent use with linezolid or methylene blue

Warnings & Precautions

  • Boxed Warning: Increased suicidal risk in patients under 25 years
  • Agranulocytosis: Rare but serious blood disorder
  • Serotonin syndrome: Risk with concurrent serotonergic drugs
  • QT prolongation: Monitor in patients with cardiac risk factors
  • Weight gain: Significant appetite stimulation and weight gain
  • Sedation: Prominent, especially early in treatment

Drug Interactions

  • MAOIs: Contraindicated – risk of serotonin syndrome
  • CNS depressants: Enhanced sedation
  • CYP1A2 inducers: May decrease mirtazapine levels
  • CYP3A4 inhibitors: May increase mirtazapine levels

Adverse Reactions

Common (≥5%):

  • Somnolence, increased appetite, weight gain, dizziness

Less Common:

  • Dry mouth, constipation, confusion, abnormal dreams

Special Populations

  • Pregnancy: Category C – use only if benefits outweigh risks
  • Elderly: Lower starting dose, monitor for falls risk
  • Hepatic impairment: Use with caution, consider dose reduction
  • Renal impairment: Use with caution in severe impairment
Medical Disclaimer: This information is for educational purposes only and is not intended as medical advice. Always consult with qualified healthcare professionals before making any treatment decisions. Individual patient circumstances may vary significantly.