Montelukast
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montelukast neuropsychiatric effects safety
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Montelukast (Singulair)
Drug Class
Leukotriene receptor antagonist (LTRA) - specifically a selective CysLT1 receptor antagonist
Mechanism of Action
Leukotrienes (LTC4, LTD4, LTE4) are produced via the 5-lipoxygenase pathway of arachidonic acid metabolism in mast cells, basophils, eosinophils, and neutrophils. These cysteinyl leukotrienes bind to CysLT1 receptors and cause:
- Bronchoconstriction
- Mucus hypersecretion
- Plasma exudation
- Eosinophil recruitment and airway inflammation
Montelukast blocks the CysLT1 receptor, preventing all of these downstream effects.
Indications
| Indication | Notes |
|---|---|
| Asthma prophylaxis (chronic) | Alternative to low-dose ICS; NOT for acute attacks |
| Exercise-induced bronchoconstriction | Give at least 2 hrs before exercise; no additional dose within 24 hrs |
| Aspirin-exacerbated respiratory disease (AERD) | Particularly effective due to high leukotriene overproduction |
| Seasonal & perennial allergic rhinitis | Adults and children; approved but NOT recommended as first-line monotherapy (inferior to intranasal corticosteroids) |
| Pediatric mild persistent asthma | Widely used in children when ICS-related growth suppression is a concern |
Pharmacokinetics
| Parameter | Detail |
|---|---|
| Route | Oral only |
| Dosing frequency | Once daily (at night) |
| Protein binding | Highly protein-bound |
| Absorption | Food does NOT impair absorption (unlike zafirlukast) |
| Metabolism | Extensive hepatic metabolism via CYP 3A4 and CYP 2C9 |
| Excretion | Biliary (feces); primarily not renal |
| Onset of effect | Rapid (hours); full chronic benefit within ~1 month |
Drug interactions: Phenobarbital and rifampin induce hepatic metabolism and increase montelukast clearance (reduced efficacy). - The Harriet Lane Handbook, 23rd ed.
Dosing
| Age Group | Indication | Dose |
|---|---|---|
| Adults & ≥15 yr | Asthma / Allergic rhinitis | 10 mg PO once daily at bedtime |
| Children 6-14 yr | Asthma / Allergic rhinitis | 5 mg (chewable tablet) PO once daily |
| Children 2-5 yr | Asthma / Allergic rhinitis | 4 mg (chewable tablet or granules) PO once daily |
| 6-23 months | Asthma only | 4 mg (oral granules) PO once daily |
| Adults ≥15 yr | Exercise-induced bronchoconstriction | 10 mg at least 2 hrs before exercise |
| Children 6-14 yr | Exercise-induced bronchoconstriction | 5 mg at least 2 hrs before exercise |
Phenylketonuria (PKU) warning: Chewable tablet contains phenylalanine - contraindicated in PKU patients. - Fishman's Pulmonary Diseases
Adverse Effects
Common
- Headache
- Abdominal pain, dyspepsia, nausea
- Diarrhea
- Fatigue, dizziness
- Elevated liver enzymes (mild; less than with zileuton)
Serious - FDA Black Box Warning
Montelukast carries an FDA black-box warning for neuropsychiatric events, including:
- Agitation, aggression
- Anxiety, dream abnormalities, insomnia
- Hallucinations
- Depression, suicidal ideation and behavior
- Obsessive-compulsive symptoms
This warning applies to both children and adults. A completed-suicide signal exists, though more recent data suggest a potentially lower risk of depression vs. inhaled corticosteroids (data remains mixed). - Goodman & Gilman's; The Maudsley Prescribing Guidelines
Rare but Serious
- Eosinophilic Granulomatosis with Polyangiitis (EGPA / Churg-Strauss syndrome): Characterized by eosinophilia, vasculitis, rash, arthralgia, worsening respiratory symptoms, and neuropathy. Often unmasked when oral corticosteroids are tapered. - Lippincott Pharmacology; Brenner & Rector's Kidney
- Stevens-Johnson syndrome / TEN (very rare, reported in children)
- Thrombocytopenia, epistaxis
Comparison with Other LTRAs
| Drug | Mechanism | Dosing | Key Concern |
|---|---|---|---|
| Montelukast | CysLT1 receptor antagonist | Once daily | Neuropsychiatric black-box warning |
| Zafirlukast | CysLT1 receptor antagonist | Twice daily (empty stomach) | Hepatotoxicity; CYP2C8/2C9/3A4 inhibitor |
| Zileuton | 5-Lipoxygenase inhibitor | Twice daily (sustained-release) | LFT monitoring required; CYP1A2 inhibitor; slightly more effective |
Zileuton inhibits both LTB4 and cysteinyl leukotrienes, making it slightly broader in spectrum but at the cost of hepatotoxicity risk. Montelukast only blocks downstream cysteinyl leukotriene effects.
Place in Therapy
- Asthma: Less effective than ICS for control; alternative for mild persistent asthma, especially in children or those unable/unwilling to use inhalers. Add-on to ICS provides modest benefit; less effective than LABA as add-on. - Katzung's; Goodman & Gilman's
- Allergic rhinitis: Equal to antihistamines in efficacy for symptom control; inferior to intranasal corticosteroids (INCS). Current AAO-HNS guidelines and 2018 International Consensus Statement recommend against routine use as monotherapy for AR. - Cummings Otolaryngology
- AERD: Particularly effective because aspirin-sensitive asthma is driven largely by leukotriene overproduction.
- Exercise-induced bronchoconstriction: Effective and avoids the tachyphylaxis seen with regular LABA use. - Harrison's 22E
- In pregnancy: LTRAs have reassuring animal data; montelukast is preferred over zileuton. - Creasy & Resnik's
- COPD: No role - cys-LTs are not elevated in exhaled breath condensate in COPD. - Goodman & Gilman's
Key Clinical Pearls
- Montelukast is not a bronchodilator - it must never be used for acute bronchospasm.
- The black-box neuropsychiatric warning (added 2020) is the most important safety caveat in current practice; counsel patients and caregivers at initiation.
- It is the only major asthma drug delivered as once-daily oral granules - useful in infants and young children who cannot use inhalers.
- No liver function test monitoring is required (unlike zileuton or zafirlukast at higher doses).
- EGPA risk may be unmasked (not directly caused) by montelukast when steroid-dependent patients are weaned off corticosteroids.
Sources: Katzung's Basic and Clinical Pharmacology 16e; Harrison's Principles of Internal Medicine 22e; Goodman & Gilman's Pharmacological Basis of Therapeutics; Lippincott Illustrated Reviews Pharmacology; The Harriet Lane Handbook 23e; Cummings Otolaryngology; Fishman's Pulmonary Diseases; Maudsley Prescribing Guidelines 15e; Creasy & Resnik's Maternal-Fetal Medicine
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