Overview
Mirtazapine is an atypical antidepressant used to treat major depressive disorder in adults. It works by enhancing noradrenergic and serotonergic neurotransmission through antagonism of central alpha-2 adrenergic receptors and serotonin receptors. The medication is known for its sedative effects and appetite stimulation, which can be beneficial in patients with insomnia or weight loss associated with depression.
Mechanism of Action
Mirtazapine acts as an antagonist at central alpha-2 adrenergic inhibitory autoreceptors and heteroreceptors, increasing norepinephrine and serotonin release. It also blocks serotonin 5-HT2 and 5-HT3 receptors, which contributes to its antidepressant effects while minimizing certain serotonin-related side effects. Additional antagonism at histamine H1 receptors explains its sedative properties.
Indications
- Treatment of major depressive disorder (MDD) in adults
Common Doses
- 7.5 mg
- 15 mg
- 30 mg
- 45 mg
Dosage
Initial dose typically 15 mg once daily at bedtime, may be increased up to 45 mg daily based on response and tolerability. Dose adjustments may be needed with CYP3A inhibitors or inducers.
Contraindications
- Concomitant use with MAOIs or within 14 days of discontinuing MAOIs
- Known hypersensitivity to mirtazapine or any tablet excipients
Side Effects
- Somnolence/sedation
- Increased appetite and weight gain
- Dizziness
- Dry mouth
- Constipation
- Elevated cholesterol and triglycerides
- Transaminase elevations
- Hyponatremia
- Orthostatic hypotension
- Activation of mania/hypomania
- Seizures
- Discontinuation syndrome
Interactions
- MAOIs: Contraindicated due to serotonin syndrome risk
- Other serotonergic drugs: Increased serotonin syndrome risk
- Strong CYP3A inducers: Decreased mirtazapine levels
- Strong CYP3A inhibitors: Increased mirtazapine levels
- Cimetidine: Increased mirtazapine levels
- Benzodiazepines and alcohol: Enhanced CNS depression
- QT-prolonging drugs: Increased arrhythmia risk
- Warfarin: May increase INR
Counseling Points
- Take at bedtime due to sedative effects
- Avoid alcohol and CNS depressants
- Report signs of infection (fever, sore throat) immediately
- Monitor for mood changes or suicidal thoughts
- Be aware of potential weight gain and increased appetite
- Do not stop abruptly due to discontinuation syndrome
- Use caution when driving or operating machinery