A patient with moderate persistent asthma is considered for add-on therapy. Which drug acts by directly inhibiting 5-lipoxygenase, thereby blocking leukotriene synthesis at its first committed step?
- A Zafirlukast
- B Zileuton ✓
- C Pranlukast
- D Montelukast
Correct answer: B. Zileuton
Explanation
Zileuton inhibits 5-lipoxygenase, the enzyme that converts arachidonic acid to leukotriene A4, so it blocks formation of all cysteinyl leukotrienes (LTC4, LTD4, LTE4). Zafirlukast, pranlukast and montelukast are leukotriene receptor antagonists acting at the CysLT1 receptor downstream of leukotriene synthesis. Hepatotoxicity requiring liver enzyme monitoring is the classic adverse effect of zileuton.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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