Montelukast is a leukotriene receptor antagonist that selectively blocks the action of cysteinyl leukotrienes (CysLTs), inflammatory mediators involved in asthma and allergic reactions. Key actions include:

1. Inhibition of Leukotriene D₄ (LTD₄): Binds to CysLT₁ receptors in the airways, preventing bronchoconstriction, mucus secretion, and vascular permeability (Lippincott).
2. Anti-inflammatory Effects: Reduces eosinophil recruitment and airway inflammation.
3. Prophylactic Role: Prevents asthma symptoms triggered by allergens, exercise, or aspirin.

Montelukast is approved for:

1. Asthma:
   • Prophylaxis and chronic treatment in adults and children ≥6 months (BNF).
   • Adjunct therapy for patients inadequately controlled by inhaled corticosteroids.
2. Allergic Rhinitis:
   • Seasonal and perennial allergic rhinitis (≥2 years).
3. Exercise-Induced Bronchoconstriction (EIB):
   • Prevention in patients ≥6 years.
4. Off-Label Uses:
   • Aspirin-exacerbated respiratory disease (AERD).
   • Chronic urticaria (limited evidence).

Adults and Adolescents (≥15 years):

• Asthma/Allergic Rhinitis: 10 mg once daily, taken in the evening.

Children:

• 6–14 years: 5 mg once daily (chewable tablet or granules).
• 2–5 years: 4 mg once daily (oral granules or chewable tablet).
• 6 months–5 years: 4 mg oral granules once daily (BNF).

Exercise-Induced Bronchoconstriction:

• 10 mg taken ≥2 hours before exercise (do not take another dose within 24 hours).

Special Populations:

• Renal/Hepatic Impairment: No dose adjustment required.

Elderly: No specific recommendations; use standard dosing

• Common (≥1%): Headache, abdominal pain, thirst, dizziness.
• Serious (Rare):
  • Neuropsychiatric effects: Agitation, depression, suicidal ideation (boxed warning).
  • Eosinophilia (with systemic symptoms).
  • Hypersensitivity reactions (angioedema, anaphylaxis).
  • Hepatic dysfunction (elevated ALT/AST).

1. Contraindications:
   • Hypersensitivity to montelukast or components.
2. Neuropsychiatric Risks:
   • Monitor for mood changes, sleep disturbances, or suicidal thoughts; discontinue if symptoms occur.
3. Pregnancy/Lactation:
   • BNF Category: Use only if benefits outweigh risks (limited human data).
   • Excreted in breast milk; avoid during lactation.

Aspirin Sensitivity: Not a substitute for aspirin avoidance in AERD

Montelukast has minimal interactions due to hepatic metabolism via CYP2C8/3A4 and renal excretion. Notable considerations:

• CYP Inducers:
  • Rifampicin, Phenobarbital: Reduce montelukast levels (monitor efficacy).
• Gemfibrozil: Inhibits CYP2C8, increasing montelukast exposure (clinical significance unclear).
• Prednisone, Theophylline: No significant interactions (Lange).

Generic & Brand Names

• Generic: Montelukast Sodium.
• Brand Names: Singulair®, Montair®, Lukast®.