What it's for (Indications)
- Mirtazapine is primarily indicated for the treatment of Major Depressive Disorder (MDD) in adults.
- This medication is effective in alleviating the diverse symptomatology associated with clinical depression, encompassing persistent low mood, anhedonia (loss of interest or pleasure), disturbances in sleep architecture (particularly insomnia and sleep fragmentation), changes in appetite and weight (often reduced in depression), psychomotor agitation or retardation, chronic fatigue, diminished concentration, feelings of worthlessness or guilt, and recurrent thoughts of death or suicidal ideation.
- Its characteristic pharmacological profile, which includes notable sedative properties, can be particularly advantageous for patients presenting with significant insomnia and anxiety as prominent features of their depressive episode.
- While some therapeutic effects on mood may be observed within one to two weeks of initiating treatment, the full antidepressant benefits typically manifest after consistent administration over four weeks or more, requiring careful clinical evaluation to ascertain complete response.
- This comprehensive action helps restore neurochemical balance crucial for mood regulation and emotional stability.
Dosage Information
| Type | Guideline |
|---|---|
| Standard | The recommended starting dose for mirtazapine is 15 mg/day, administered as a single dose, preferably in the evening prior to sleep. The effective dose range for major depressive disorder is generally 15 to 45 mg/day, with a maximum recommended dose of 45 mg/day. Patients not responding to the initial 15-mg dose may benefit from dose increases up to the maximum. Due to its elimination half-life of approximately 20 to 40 hours, dose changes should not be made at intervals of less than one to two weeks to allow for sufficient evaluation of the therapeutic response. Clearance of mirtazapine is reduced in elderly patients and those with renal or hepatic impairment, necessitating careful consideration of dosage in these populations. |
Safety & Warnings
Common Side Effects
- Common side effects include somnolence (drowsiness), nausea, weight gain, increased appetite, abnormal dreams, confusion, anxiety, insomnia, headache, lethargy, dizziness, tremor, sedation, orthostatic hypotension (sudden low blood pressure on standing up), dry mouth, gastrointestinal (GI) upset, rash, arthralgia (pain in joints), myalgia (pain in muscles), back pain, peripheral edema (accumulation of fluid in the fingers and toes), and fatigue.
- Rare but serious adverse effects reported include hyponatremia (decreased sodium in the blood) and agranulocytosis (decreased white blood cells).
- Patients should be warned to report any signs of infection, and treatment should be stopped with blood counts performed if an infection occurs.
Serious Warnings
- Black Box Warning: Antidepressants increased the risk compared to placebo of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults in short-term studies of major depressive disorder (MDD) and other psychiatric disorders. Anyone considering the use of mirtazapine or any other antidepressant in a child, adolescent, or young adult must balance this risk with the clinical need. Short-term studies did not show an increase in the risk of suicidality with antidepressant use in adults beyond age 24; there was a reduction in risk with antidepressant use in adults aged 65 and older.
- Antidepressants, including mirtazapine, have been shown to increase the risk of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults in short-term studies for major depressive disorder and other psychiatric disorders.
- This risk must be balanced against clinical need, and patients should be monitored for suicidal ideation.
- Use with caution in patients with liver or kidney impairment (as clearance is reduced), epilepsy, organic brain syndrome (a condition which causes a gradual decrease in brain function), diabetes, angina, heart conduction disturbance, recent myocardial infarction (MI), hypotension (low blood pressure), prostatic hypertrophy (increase in size of prostate), narrow-angle glaucoma, or increased intraocular pressure.
- Caution is also advised in patients with a history of mania (a condition which is marked by periods of overactivity and delusions) or psychosis.
- Discontinue treatment if jaundice occurs.
- Dose increases may be detrimental in patients who develop akathisia (a movement disorder characterized by a feeling of inner restlessness and inability to stay still).
How it Works (Mechanism of Action)
Mirtazapine operates as a noradrenergic and specific serotonergic antidepressant (NaSSA), exhibiting a unique multi-modal mechanism of action that differentiates it from other antidepressant classes. Its principal action involves potent antagonism of central presynaptic alpha-2 adrenergic autoreceptors and heteroreceptors. By blocking these inhibitory receptors, mirtazapine effectively enhances the release of both norepinephrine and serotonin (5-hydroxytryptamine, 5-HT) into the synaptic cleft, particularly in key brain regions involved in mood regulation. Crucially, mirtazapine also acts as an inverse agonist or antagonist at several postsynaptic serotonin receptor subtypes, specifically 5-HT2A, 5-HT2C, and 5-HT3 receptors. Antagonism of 5-HT2A and 5-HT2C receptors is believed to contribute significantly to its antidepressant and anxiolytic efficacy, while simultaneously mitigating common serotonin-related adverse effects such as sexual dysfunction, anxiety, and gastrointestinal disturbances, which are often observed with selective serotonin reuptake inhibitors (SSRIs). Furthermore, its antagonism of 5-HT3 receptors may offer anti-emetic benefits. A notable aspect of mirtazapine's pharmacology is its potent antagonism of histamine H1 receptors, which is largely responsible for its prominent sedative effects, especially at lower therapeutic doses, and its propensity to cause increased appetite and subsequent weight gain. The drug demonstrates comparatively weaker affinity for muscarinic cholinergic and alpha-1 adrenergic receptors, contributing to a more favorable profile regarding anticholinergic and orthostatic hypotensive side effects than many older antidepressants.