respiratory:drugs:zafirlukast []

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====== Zafirlukast ======

===== Classification =====
  * Leukotriene Receptor Antagonist (CysLT1 blocker)

Parent class:
  * [[respiratory:drug_classes:leukotriene_modifiers|Leukotriene Modifiers]]

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===== Mechanism of Action =====

Zafirlukast selectively blocks the CysLT1 receptor.

Leukotrienes (LTC4, LTD4, LTE4) normally cause:

  * Bronchoconstriction
  * Increased mucus secretion
  * Increased vascular permeability
  * Eosinophilic airway inflammation

By blocking CysLT1:

  * ↓ Bronchospasm
  * ↓ Airway inflammation
  * ↓ Mucus production

Does NOT inhibit leukotriene synthesis.

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===== Pharmacokinetics =====

  * Oral administration
  * Twice-daily dosing
  * Hepatic metabolism (CYP2C9)
  * Eliminated via bile

Absorption reduced by food — take on empty stomach.

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===== Indications =====

  * [[respiratory:clinical:asthma|Asthma]] (maintenance therapy)

Not indicated for:
  * Acute asthma exacerbations

Less commonly used than [[respiratory:drugs:montelukast|Montelukast]].

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===== Dosing (Adult) =====

  * 20 mg PO twice daily
  * Take 1 hour before or 2 hours after meals

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===== Adverse Effects =====

Common:
  * Headache
  * GI upset

Serious:
  * Hepatotoxicity (rare)
  * Elevated liver enzymes

Monitor LFTs if clinically indicated.

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===== Drug Interactions =====

  * Inhibits CYP2C9
  * May increase warfarin levels (monitor INR)
  * Food reduces absorption

Fewer neuropsychiatric warnings compared to montelukast.

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===== Clinical Role =====

Compared to montelukast:

  * Requires twice-daily dosing
  * Food restrictions reduce convenience
  * More drug interaction potential
  * Less commonly prescribed

May be considered in:

  * Patients who cannot tolerate montelukast
  * Certain asthma phenotypes

See:
  * [[respiratory:clinical:asthma|Asthma Management]]

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===== Comparison Within Class =====

^ Drug ^ Mechanism ^ Major Risk ^
| [[respiratory:drugs:montelukast|Montelukast]] | CysLT1 blocker | Neuropsychiatric effects |
| [[respiratory:drugs:zafirlukast|Zafirlukast]] | CysLT1 blocker | Hepatotoxicity |
| [[respiratory:drugs:zileuton|Zileuton]] | 5-LO inhibitor | Hepatotoxicity |

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===== Clinical Pearls =====

  * Must be taken on empty stomach.
  * Less convenient than montelukast.
  * Can increase warfarin levels.
  * Not effective for acute asthma attacks.
  * Used far less commonly in current practice.

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===== Related Pages =====

  * [[respiratory:drug_classes:leukotriene_modifiers|Leukotriene Modifiers]]
  * [[respiratory:drugs:montelukast|Montelukast]]
  * [[respiratory:clinical:asthma|Asthma]]