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Mirtazapine

Class: Antidepressants, Miscellaneous
- Tetracyclic Antidepressants
VA Class: CN609
Chemical Name: 1,2,3,4,10,14b-Hexahydro-2-methylpyrazino[2,1-a]pyrido [2,3-c][2]benzazepine
Molecular Formula: C17H19N3
CAS Number: 61337-67-5
Brands: Remeron

Medically reviewed by Drugs.com on Apr 21, 2021. Written by ASHP.

Warning

    Suicidality in Children and Adolescents
  • Antidepressants may increase risk of suicidal thinking and behavior (suicidality) in children and adolescents with major depressive disorder and other psychiatric disorders (See Pediatric Use under Cautions); balance this risk with clinical need. Mirtazapine is not approved for use in pediatric patients.

  • Closely monitor pediatric patients who are started on mirtazapine therapy for clinical worsening, suicidality, or unusual changes in behavior; involve family members and/or caregivers in this process. (See Worsening of Depression and Suicidality Risk under Cautions.)

Introduction

Tetracyclic antidepressant; a piperazinoazepine-derivative.

Uses for Mirtazapine

Major Depressive Disorder

Treatment of major depressive disorder.

Mirtazapine Dosage and Administration

General

  • Allow at least 2 weeks to elapse between discontinuance of an MAO inhibitor and initiation of mirtazapine, and vice versa.

  • Monitor for possible worsening of depression or suicidality, especially at the beginning of therapy or during periods of dosage adjustments. (See Worsening of Depression and Suicidality Risk under Cautions.)

  • Sustained therapy may be required; monitor periodically for need for continued therapy.

  • Maximum antidepressant effects of therapy may not be evident until ≥4 weeks of treatment.

Administration

Oral Administration

Administer orally as conventional tablets and orally disintegrating tablets once daily (at bedtime) without regard to meals.

Do not break orally disintegrating tablets.

Just prior to administration of orally disintegrating tablet, remove tablet from blister package; peel open blister package, place tablet on tongue to dissolve, and swallow with saliva; administration with liquid is not necessary.

Dosage

Adults

Major Depressive Disorder
Oral

Initially, 15 mg daily. If no improvement, dosage may be increased up to a maximum of 45 mg daily at intervals of not less than 1–2 weeks.

Prescribing Limits

Adults

Major Depressive Disorder
Oral

Maximum 45 mg daily.

Special Populations

Hepatic Impairment

Decreased clearance; however, no special population dosage recommendations at this time. (See Hepatic Impairment under Cautions.)

Renal Impairment

Decreased clearance in patients with moderate to severe renal impairment; however, no special population dosage recommendations at this time. (See Renal Impairment under Cautions.)

Geriatric Patients

Select dosage with caution because of age-related decreases in hepatic, renal, and/or cardiac function and concomitant disease and drug therapy.

Cautions for Mirtazapine

Contraindications

  • Known hypersensitivity to mirtazapine or any ingredient in the formulation.

Warnings/Precautions

Warnings

Worsening of Depression and Suicidality Risk

Possible worsening of depression and/or emergence of suicidal ideation and behavior (suicidality); may persist until clinically important remission occurs with therapy. Closely supervise patients with major depressive disorder or other psychiatric illness with comorbid depression during initiation of therapy and during periods of dosage adjustments. (See Boxed Warning.)

If anxiety, agitation, panic attacks, insomnia, irritability, hostility, impulsivity, akathisia, hypomania, and/or mania occur, consider changing or discontinuing therapy, particularly if severe, abrupt in onset, or not a part of patient’s presenting symptoms.

Prescribe in smallest quantity consistent with good patient management to reduce risk of overdosage.

Observe these precautions for patients with psychiatric (e.g., major depressive disorder, obsessive-compulsive disorder) or nonpsychiatric disorders.

Bipolar Disorder

May unmask bipolar disorder. (See Activation of Mania or Hypomania under Cautions.)

Screen for risk of bipolar disorder by obtaining detailed psychiatric history (e.g., family history of suicide, bipolar disorder, depression) prior to initiating therapy.

Hematologic Effects

Agranulocytosis or severe neutropenia (with or without infection) reported rarely. If signs of infection (e.g., sore throat, fever, stomatitis) and low WBC counts occur, discontinue therapy and monitor patient closely.

Drug Interactions

Concomitant use with an MAO inhibitor associated with serious, sometimes fatal reactions, including manifestations resembling serotonin syndrome (e.g., hyperthermia, rigidity, myoclonus, autonomic instability, mental status changes) or neuroleptic malignant syndrome. (See Specific Drugs under Interactions.)

General Precautions

CNS Effects

Risk of impaired mental alertness or physical coordination required for performing hazardous tasks (e.g., driving, operating machinery).

Possible dizziness.

Altered Appetite and Weight

Possible increased appetite and weight gain.

Hyperlipidemia

Clinically important increases in serum cholesterol (e.g., >20% ULN) and serum triglyceride (e.g., 500 mg/dL) concentrations reported.

Hepatic Effects

Potentially clinically important elevations (e.g., 3 times ULN) in serum ALT concentrations; not usually associated with impaired hepatic function.

Activation of Mania or Hypomania

Possible activation of mania or hypomania; use with caution in patients with a history of mania or hypomania. (See Bipolar Disorder under Cautions.)

Seizures

Risk of seizures; use with caution in patients with a history of seizures.

Concomitant Illnesses

Experience in patients with concomitant diseases is limited.

Use with caution in patients with concomitant illnesses affecting metabolism or hemodynamic response.

Cardiovascular Effects

Safety in patients with recent history of MI or those with unstable heart disease not established.

Orthostatic hypotension reported infrequently. Use with caution in patients with known cardiovascular or cerebrovascular disease and in patients with conditions that predispose them to hypotension (e.g., dehydration, hypovolemia, concurrent antihypertensive therapy).

Possible increased heart rate and changes in ECG; clinical significance not known.

Phenylketonuria

Remeron SolTab orally disintegrating tablets contain aspartame (e.g., NutraSweet), which is metabolized in the GI tract to provide 2.6, 5.2, and 7.8 mg of phenylalanine per 15, 30, and 45 mg tablet, respectively.

Specific Populations

Pregnancy

Category C.

Lactation

Not known whether mirtazapine is distributed into milk. Caution if used in nursing women.

Pediatric Use

Safety and efficacy not established.

Geriatric Use

No substantial differences in adverse effects relative to younger adults; however, increased sensitivity to sedative effects possible in some geriatric individuals.

Use with caution in patients >65 years of age.

Hepatic Impairment

Decreased clearance; use with caution.

Renal Impairment

Decreased clearance in patients with moderate to severe renal impairment; use with caution.

Common Adverse Effects

Somnolence, increased appetite, weight gain, dizziness.

Interactions for Mirtazapine

Metabolized by CYP2D6, CYP3A4, and CYP1A2; not a potent inhibitor of CYP2D6, CYP3A4, and CYP1A2.

Drugs Affecting Hepatic Microsomal Enzymes

Potential pharmacokinetic interaction (decreased mirtazapine metabolism) with inhibitors of CYP2D6, CYP3A4, or CYP1A2.

Potential pharmacokinetic interaction (increased mirtazapine metabolism) with inducers of CYP2D6, CYP3A4, or CYP1A2.

Drugs Metabolized by Hepatic Microsomal Enzymes

Substrates of CYP2D6, CYP3A4, or CYP1A2: potential pharmacokinetic interaction (decreased plasma substrate concentrations). However, mirtazapine is not a potent inhibitor of these enzymes and clinically important interaction is unlikely.

Specific Drugs

Drug

Interaction

Comments

Alcohol

Potentiates cognitive and motor effects of alcohol

Concomitant use is not recommended

Benzodiazepines (diazepam)

Additive sedative effects

Concomitant use is not recommended

MAO inhibitors

Possible serotonin or neuroleptic malignant syndrome

Concomitant use is not recommended

Allow at least 2 weeks to elapse between discontinuance of an MAO inhibitor and initiation of mirtazapine, or vice versa

Mirtazapine Pharmacokinetics

Absorption

Bioavailability

Well absorbed from the GI tract following oral administration, with peak plasma concentration usually attained within 2 hours.

Bioavailability is approximately 50%.

Food

Food does not appear to affect absorption.

Distribution

Extent

Not known whether distributed into milk.

Plasma Protein Binding

Approximately 85%.

Elimination

Metabolism

Extensively metabolized in the liver, via CYP2D6 and CYP1A2 to the 8-hydroxy metabolite, and via CYP3A4 to the N-desmethyl and N-oxide metabolite .

Elimination Route

Excreted in urine (75%) and feces (15%).

Half-life

20–40 hours.

Special Populations

Renal impairment may reduce clearance.

Hepatic impairment may reduce clearance.

Stability

Storage

Oral

Tablets and Orally Disintegrating Tablets

25°C in the original container; protect from light and moisture.

Actions

  • Mechanism of action as an antidepressant is unclear, but is presumed to be linked to potentiation of noradrenergic and serotonergic activity in the CNS resulting from its antagonism at central presynaptic α2-adrenergic autoreceptors and heteroreceptors.

  • Exhibits potent antagonism of serotonin type 2 (5-HT2) and type 3 (5-HT3) receptors; does not exhibit high affinity for serotonin type 1A (5-HT1A) or type 1B (5-HT1B) receptors.

  • Exhibits potent antagonism of histamine H1 receptors.

  • Exhibits moderate peripheral α1-adrenergic blocking activity and moderate antagonism at muscarinic receptors.

Advice to Patients

  • Risks of suicidality; importance of patients, caregivers, and families immediately reporting emergence of suicidality, worsening depression, or other manifestations associated with increased risk of worsening depression or suicidality.

  • Importance of considering possible impaired ability to perform hazardous activities (e.g., operating machinery, driving a motor vehicle); avoid driving or operating machinery until effects on individual are known.

  • Importance of avoiding alcohol-containing beverages or products.

  • Importance of continuing therapy even if improvement is evident within 1–4 weeks, unless directed otherwise. Importance of patients not discontinuing therapy without first consulting clinician.

  • Importance of not breaking orally disintegrating tablets.

  • Importance of informing patients with phenylketonuria that orally disintegrating tablets contain aspartame.

  • Importance of patients informing clinicians of existing or contemplated concomitant therapy, including prescription and OTC drugs, as well as concomitant illnesses.

  • Importance of women notifying clinicians if they are or plan to become pregnant or plan to breast-feed.

  • Importance of informing patients of other important precautionary information. (See Cautions.)

Preparations

Excipients in commercially available drug preparations may have clinically important effects in some individuals; consult specific product labeling for details.

Please refer to the ASHP Drug Shortages Resource Center for information on shortages of one or more of these preparations.

* available from one or more manufacturer, distributor, and/or repackager by generic (nonproprietary) name

Mirtazapine

Routes

Dosage Forms

Strengths

Brand Names

Manufacturer

Oral

Tablets, film-coated

15 mg*

Remeron (scored)

Organon

30 mg*

Remeron (scored)

Organon

45 mg*

Remeron

Organon

Tablets, orally disintegrating

15 mg

Remeron SolTab (with aspartame)

Organon

30 mg

Remeron SolTab (with aspartame)

Organon

45 mg

Remeron SolTab (with aspartame)

Organon

AHFS DI Essentials™. © Copyright 2022, Selected Revisions May 1, 2007. American Society of Health-System Pharmacists, Inc., 4500 East-West Highway, Suite 900, Bethesda, Maryland 20814.

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