Cys leukotriene receptor antagonists
Always check the BNF or equivalent for prescribing advice.
LTRAs (e.g. Montelukast, Zafirlukast) are oral anti-asthma drugs used mainly as add-on therapy.
⚙️ Mode of Action
- Leukotrienes (esp. LTC₄, LTD₄, LTE₄) are key mediators of bronchoconstriction, airway oedema, and mucus secretion.
- LTRAs block these mediators at the CysLT₁ receptor.
- Provide mild bronchodilation and some anti-inflammatory effect (though less than inhaled corticosteroids).
🎯 Indications
- 🌬️ Asthma (Step 3 add-on, BTS/SIGN guidelines): For patients uncontrolled on low-dose inhaled corticosteroid (ICS), usually added before LABA in young children.
- 👶 Paediatrics: Sometimes used earlier in children unable to use inhalers effectively.
- 📉 Steroid-sparing: For patients intolerant of ICS (though not as effective).
- ❓ COPD: Role unclear, not recommended routinely.
⛔ Contraindications
- ⚠️ Churg–Strauss Syndrome (eosinophilic granulomatosis with polyangiitis): Rare association with LTRA use, particularly when tapering steroids.
- Hypersensitivity to active drug or excipients.
💊 Examples
- Montelukast: Most widely prescribed; once-daily oral tablet, chewable paediatric formulations available.
- Zafirlukast: Less commonly used in the UK; potential drug–drug interactions (esp. with warfarin).
💢 Side Effects
- 🩸 Churg–Strauss–like illness: eosinophilia, vasculitic rash, sinusitis, worsening asthma.
- 🧠 Neuropsychiatric effects: agitation, depression, sleep disturbance, suicidal thoughts (rare; MHRA safety update 2019).
- 🩺 Headache, abdominal pain, GI upset.
🔄 Interactions
- Zafirlukast + Warfarin: ↑ INR → bleeding risk.
- Fewer significant interactions with montelukast.
📚 References
- BNF: Montelukast
- MHRA Drug Safety Update 2019: Montelukast neuropsychiatric reactions
- BTS/SIGN Asthma Guidelines
