Zileuton differs from montelukast and zafirlukast in asthma therapy. Which statement correctly describes this difference?

• A Zileuton blocks the cysteinyl-leukotriene receptor whereas the others inhibit leukotriene synthesis
• B Zileuton inhibits phosphodiesterase-4 and elevates intracellular cAMP
• C Zileuton inhibits 5-lipoxygenase, blocking formation of all leukotrienes including LTB4 ✓
• D Zileuton antagonises the thromboxane receptor on platelets

Explanation

Montelukast and zafirlukast are cysteinyl-leukotriene (LTC4, LTD4, LTE4) receptor antagonists. Zileuton instead inhibits 5-lipoxygenase, the enzyme converting arachidonic acid to leukotriene A4, so it blocks synthesis of both bronchoconstrictor cysteinyl-leukotrienes and LTB4, a neutrophil chemoattractant. Because of this broader action and hepatic metabolism, zileuton requires monitoring of liver transaminases during therapy, a feature the receptor antagonists do not share.

Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.

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