| Recommended Dose and Dosage Regimen | The recommended dose of mirtazapine for the treatment of depression varies depending on the individual patient’s response and tolerability. For adults, the usual starting dose is 15 mg orally once daily, administered at bedtime. The dose may be gradually titrated upwards by 15 mg increments every 1-2 weeks, up to a maximum dose of 45 mg daily. Elderly patients or those with hepatic impairment may require lower starting doses and slower titration. Follow your healthcare provider’s instructions regarding dosing and administration. |
| Frequency of Administration | Mirtazapine is typically administered orally once daily, preferably at bedtime due to its sedating effects. |
| Route of Administration | Mirtazapine is available as oral tablets or orally disintegrating tablets for ingestion. |
| Mechanism of Action (MOA) | Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA) that exerts its pharmacological effects by enhancing noradrenergic and serotonergic neurotransmission in the central nervous system. Mirtazapine antagonizes presynaptic alpha-2 adrenergic receptors, leading to increased release of norepinephrine and serotonin in the synaptic cleft. Additionally, mirtazapine blocks postsynaptic serotonin 5-HT2 and 5-HT3 receptors, which may contribute to its antidepressant, anxiolytic, and antiemetic properties. Mirtazapine also has potent histamine H1 receptor antagonism, resulting in sedation and weight gain. |
| Pharmacokinetics (PK) | Mirtazapine is well absorbed after oral administration, with peak plasma concentrations reached within 2 hours. It undergoes extensive hepatic metabolism via cytochrome P450 enzymes, primarily CYP2D6 and CYP3A4, to form pharmacologically active metabolites. The elimination half-life of mirtazapine is approximately 20-40 hours, allowing for once-daily dosing. Mirtazapine and its metabolites are predominantly eliminated in the urine and feces. Dosage adjustments are necessary in patients with hepatic impairment or concomitant use of potent CYP3A4 inhibitors or inducers. |
| Pharmacodynamics (PD) | Mirtazapine exerts its pharmacodynamic effects by modulating neurotransmitter systems implicated in the pathophysiology of depression and anxiety disorders. By enhancing noradrenergic and serotonergic neurotransmission in the brain, mirtazapine increases synaptic levels of norepinephrine and serotonin, leading to antidepressant and anxiolytic effects. Mirtazapine’s antagonism of histamine H1 receptors contributes to its sedative properties, while its blockade of serotonin 5-HT2 and 5-HT3 receptors may alleviate symptoms such as insomnia and nausea. Mirtazapine also has mild anticholinergic effects, which may contribute to its tolerability profile. |
| Pathophysiology | Mirtazapine is indicated for the treatment of major depressive disorder (MDD) in adults. Major depressive disorder is a common mood disorder characterized by persistent feelings of sadness, hopelessness, and loss of interest or pleasure in daily activities. MDD is associated with significant functional impairment and increased risk of suicide. The pathophysiology of MDD involves complex interactions between genetic, biological, psychological, and environmental factors, resulting in dysregulation of neurotransmitter systems such as serotonin, norepinephrine, and dopamine in the brain. |
| Primary Indications | Major depressive disorder (MDD) in adults. |
| Contraindications | Contraindications to mirtazapine use include hypersensitivity to mirtazapine or any component of the formulation, concomitant use of monoamine oxidase inhibitors (MAOIs) or within 14 days of discontinuing MAOI therapy, and acute or severe hepatic impairment. Mirtazapine should be used with caution in patients with a history of seizure disorders, angle-closure glaucoma, urinary retention, or cardiovascular disease, as well as in elderly patients or those at risk of falls. |
| Purpose of Taking Medication | The purpose of mirtazapine therapy is to alleviate symptoms of major depressive disorder (MDD) in adults, including depressed mood, anhedonia, fatigue, sleep disturbances, appetite changes, and psychomotor agitation or retardation. Mirtazapine is used as a first-line antidepressant agent and may be prescribed alone or in combination with other antidepressants to achieve remission of depressive symptoms, improve functional status, and enhance quality of life. |
| Usage Instructions | Take mirtazapine orally as directed by your healthcare provider, usually once daily at bedtime to minimize sedation. Swallow the tablets whole with water; do not crush, chew, or split the tablets unless instructed otherwise. If using orally disintegrating tablets, allow the tablet to dissolve on the tongue without water and swallow the dissolved medication. Follow your healthcare provider’s instructions regarding dosing schedule, titration, and adjustments. |
| Precautions and Care | Patients taking mirtazapine should be closely monitored for signs of clinical improvement, as well as adverse effects such as sedation, weight gain, dizziness, orthostatic hypotension, and hyponatremia. Use caution when initiating or discontinuing mirtazapine therapy, as abrupt changes in dosage may precipitate withdrawal symptoms or exacerbate depressive symptoms. Monitor for the emergence of suicidal ideation or behavior, particularly in young adults or during the initial phase of treatment. |
| Dietary Considerations | There are no specific dietary restrictions associated with mirtazapine use. Maintain a balanced diet and adequate hydration to support overall health and well-being during depression management. Avoid excessive alcohol consumption, as it may potentiate the central nervous system depressant effects of mirtazapine and increase the risk of adverse reactions. |
| Missed Dose | If a dose of mirtazapine is missed, take it as soon as remembered, unless it is almost time for the next scheduled dose. Do not double the dose to make up for a missed one. Resume the regular dosing schedule and consult your healthcare provider if unsure about missed doses or medication instructions. |
| Possible Side Effects | Common side effects of mirtazapine may include drowsiness, sedation, weight gain, increased appetite, dry mouth, constipation, dizziness, and blurred vision. Less common side effects may include orthostatic hypotension, tachycardia, urinary retention, and sexual dysfunction. Contact your healthcare provider if you experience severe or persistent side effects while taking mirtazapine. |
| Storage and Disposal | Store mirtazapine tablets at room temperature away from moisture and heat. Keep the medication out of reach of children and pets. Unused or expired medication should be disposed of properly according to local regulations or guidelines for pharmaceutical waste disposal. |
| Overdose or Emergency | In case of mirtazapine overdose or emergency, seek immediate medical attention or contact a poison control center. Overdose may lead to excessive sedation, cardiovascular effects (e.g., tachycardia, hypotension), anticholinergic effects, and central nervous system depression. Treatment of mirtazapine overdose may involve supportive care, activated charcoal, gastric lavage, and symptomatic management of adverse effects. |
| Monitoring and Laboratory Tests | Patients receiving mirtazapine therapy require regular monitoring of depressive symptoms, as well as vital signs, weight, and laboratory parameters such as electrolytes, renal function, and hepatic function. Consider baseline and periodic electrocardiograms (ECGs) in patients at increased risk of cardiac conduction abnormalities or arrhythmias. Monitor for the emergence of adverse effects and therapeutic response during mirtazapine treatment. |
