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Mirtazapine

Brands and Forms

  • Remeron
    • tablet: 15mg, 30mg, 45mg
  • Remeron SolTab
    • orally disintegrating tablet: 15mg, 30mg, 45mg
  • Mirtazipine
    • tablet: 7.5mg

Uses of Mirtazapine

Mirtazapine is used for treating Depressive Disorders and Anxiety Disorders. It may be a particularly good choice for cases where insomnia and loss of appetite are very significant problems, as it can be very sedating and also cause increased appetite and weight gain.

How Mirtazapine Works

Mirtazapine blocks adrenergic alpha-2 receptors, serotonin 2a, 2c and 3 receptors, and histamine H1 receptors. This results in an increase in serotonin and noradrenaline transmission in the central nervous system, which occurs independently of serotonin and norepinephrine reuptake blockade.

Cautions when Using Mirtazapine

Mirtazapine can induce Manic or Mixed Episodes and Rapid Cycling in people with Bipolar Disorder.

Children and adolescents who use antidepressants like Mirtazapine may develop self-injurious or suicidal behaviors (for more information, see here).

Use with caution in people with a known seizure disorder, in those who are taking anticoagulant (blood thinning) medication, and in people with cardiovascular or cerebrovascular disease whose condition could be exaccerbated by hypotension.

Long-term use of Mirtazapine may be associated with increased risk of osteoporosis and bone fractures in individuals over age 50.

Mirtazapine should not be used during or within 14 days following the administration of an MAOI, because a hypertensive crisis may result.

Dosing of Mirtazapine

Initial dose is 15mg before bedtime, and it can be increased in 15mg increments as quickly as every week to a maximum of 45mg at bedtime. In rare cases, doses as high as 90mg at bedtime can be used.

It is recommended to wait for about 4 weeks at 15mg daily for therapeutic effects to occur before deciding to increase the dose.

Sedation may be more pronounced at lower doses.

When wanting to stop this medication, the dose should be decreased gradually over a period of a few weeks. A sudden cessation of the medication can result in a discontinuation syndrome.

Onset of action

Therapeutic effects are not expected before 2-4 weeks at a dose of 15mg a day. If no significant effects are seen after 6-8 weeks of use, including at least 2 weeks at a dose of 30mg or more daily, then the medication may not work at all.

Kidney impairment

Use with caution. Mirtazapine clearance reduced by 50% in people with severe kidney impairment (CrCl less than 10 mL/min).

Liver impairment

Use with caution.

Side-effects of Mirtazapine

Below is a list of most of the reported side-effects of Mirtazapine. Most of these side-effects occur in only a minority of individuals, and many also resolve with time while the medication is continued.

Cardiovascular: hypertension; palpitations; postural hypotension; tachycardia; vasodilatation.

Central Nervous System: somnolence; weakness; dizziness; abnormal dreams; confusion; tremor; memory problems; headache; hypesthesia; hypertonia; insomnia; paresthesia; twitching; vertigo; seizures (rare); serotonin syndrome (rare).

Dermatologic: itchiness; rash.

Endocrine/ Metabolic: elavated lipids and cholesterol.

Eyes, Ears, Nose and Throat: blurred vision; accommodation difficulties.

Gastrointestinal: dry mouth; constipation; nausea; abdominal pain; increased appetite; weight gain; diarrhea; dyspepsia; flatulence; vomiting.

Genitourinary: urinary frequency; decreased libido (about 1%).

Hematologic: increases bleeding time (thins the blood).

Muskuloskeletal: back pain; muscle pain; join pain; long-term use may increase risk of osteoporosis and bone fractures, especially in individuals above age 50.

Psychiatric: anxiety; agitation; apathy; worsening depression; suicidal thoughts (overall, Mirtazapine use helps to lower risk of suicide); self-injurious behaviors among children and adolescents; can induce Manic or Mixed Episodes and Rapid Cycling in people with Bipolar Disorder.

Respiratory: shortness of breath; increased cough; sinusitis.

Common side-effects of Mirtazapine

Somnolence (may be greater at lower doses), dry mouth, increased appetite, weight gain, constipation.

Rare but serious side-effects of note of Mirtazapine

  • Children and adolescents who use antidepressants like Mirtazapine may develop self-injurious or suicidal behaviors (for more information, see here).
  • Seizures

Mirtazapine discontinuation syndrome

Individuals who suddenly stop using Mirtazapine after taking the medication at moderate or high doses over a significant period of time are at risk of developing a discontinuation syndrome, which can include anxiety, restlessness, irritability, nausea, vomiting, and insomnia. These symptoms usually start anywhere from one day to one week after the medication was stopped, and can persists for days or even weeks.

This syndrome can be treated by restarting the medication at its prior dose. It can be prevented by decreasing the dose gradually over a period of a few weeks when wanting to stop the medication. In rare cases, individuals may experience the discontinuation syndrome even when the medication is being tapered gradually; in such cases, an extremely slow and gradual taper will be necessary.

Mirtazapine overdose

Disorientation, drowsiness, impaired memory, tachycardia.

Mirtazapine and pregnancy

Category C: some animal studies show adverse effects at very high doses, but no controlled human studies have been done; should only be used in pregnancy if clearly needed and if benefits outweigh potential risks. For further information, see the section on treating Depression in pregnancy.

Medical Monitoring for Mirtazapine

Monitor weight, body mass index, glucose and lipid profile.

Drug Interactions with Mirtazapine

  • Caution should be used when combining Mirtazapine with other medications that can increase bleeding time and reduce blood clotting, including Aspirin, NSAIDs, anti-platelet agents, Heparin and Coumadin.
  • Combination with other serotonergic medications, including SSRI antidepressants, could in very rare cases precipitate a serotonin syndrome.
  • Mirtazapine blood concentrations can be lowered by Phenytoin.
  • Mirtazapine should not be used during or within 14 days following the administration of an MAOI, because a hypertensive crisis may result.