Montelukast exerts its anti-asthmatic effects by blocking which receptor, and which specific cysteinyl leukotrienes does it antagonize?

• A 5-lipoxygenase enzyme, blocking synthesis of all leukotrienes (LTB4, LTC4, LTD4, LTE4)
• B CysLT1 receptor, blocking the actions of LTC4, LTD4, and LTE4 on bronchial smooth muscle ✓
• C Thromboxane receptor, preventing bronchoconstriction and platelet activation
• D BLT1 receptor, blocking LTB4-mediated neutrophil chemotaxis

Explanation

Montelukast is a potent competitive antagonist at the cysteinyl leukotriene type 1 (CysLT1) receptor, which mediates the bronchoconstrictor, mucus-secretory, and mucosal edema effects of LTC4, LTD4, and LTE4. These cys-leukotrienes are synthesised from arachidonic acid via 5-lipoxygenase and are particularly elevated in aspirin-exacerbated respiratory disease, exercise-induced bronchoconstriction, and allergic asthma. Zileuton (not montelukast) inhibits 5-lipoxygenase (option A). LTB4 acts on BLT receptors promoting neutrophil chemotaxis (option D).

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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