Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA) used primarily for the treatment of major depressive disorder (MDD). The 7.5mg strength is a low dose, often used for initiation of therapy, in elderly patients, or for patients sensitive to side effects. It is known for its sedative and appetite-stimulating effects, which can be beneficial in patients with insomnia or weight loss associated with depression.
Adult: Initial dose: 15mg once daily, preferably at bedtime. The 7.5mg dose is used for initiation in patients who are particularly sensitive to side effects or as a step-down during titration. Dose can be increased up to 45mg/day based on response.
Note: Take orally, preferably at bedtime due to sedative effects. Can be taken with or without food. Tablet should be swallowed whole with water; do not crush or chew.
Mirtazapine is a potent antagonist of central presynaptic alpha-2 adrenergic autoreceptors and heteroreceptors. This blockade increases the release of both norepinephrine and serotonin. It is also a potent antagonist of postsynaptic 5-HT2 and 5-HT3 receptors, which is thought to enhance 5-HT1A-mediated serotonergic transmission and reduce side effects like anxiety, insomnia, and nausea.
Pregnancy: Pregnancy Category C (US FDA). Animal studies show adverse effects. Use only if potential benefit justifies potential fetal risk. Neonates exposed late in third trimester may develop complications like respiratory distress, feeding difficulties, and withdrawal syndrome. Consult an obstetrician.
Driving: May impair ability to drive or operate machinery, especially during the first week of treatment or after dose increases. Advise patients not to drive if they feel drowsy or dizzy.
| Monoamine Oxidase Inhibitors (MAOIs) - e.g., Phenelzine, Selegiline | Risk of serotonin syndrome, hyperthermia, rigidity, myoclonus. | Contraindicated |
| Other CNS Depressants (e.g., Alcohol, Benzodiazepines, Opioids) | Additive sedation, impaired psychomotor performance, respiratory depression. | Major |
| Strong CYP3A4 Inhibitors (e.g., Ketoconazole, Clarithromycin) | Increased Mirtazapine plasma levels, risk of side effects. | Moderate |
| Strong CYP3A4 Inducers (e.g., Rifampicin, Carbamazepine) | Decreased Mirtazapine plasma levels, reduced efficacy. | Moderate |
| Serotonergic Drugs (e.g., SSRIs, SNRIs, Tramadol, Linezolid) | Increased risk of serotonin syndrome. | Moderate to Major |
Same composition (Mirtazapine (7.5mg)), different brands: