Zileuton is used as add-on therapy in asthma because of its action on the leukotriene pathway. Its mechanism of action differs fundamentally from montelukast in that zileuton:
- A Blocks cysteinyl leukotriene receptors on bronchial smooth muscle
- B Inhibits cyclooxygenase-1, reducing thromboxane synthesis
- C Inhibits 5-lipoxygenase, preventing formation of all leukotrienes from arachidonic acid ✓
- D Antagonizes the LTB4 receptor on neutrophils
Correct answer: C. Inhibits 5-lipoxygenase, preventing formation of all leukotrienes from arachidonic acid
Explanation
Zileuton directly inhibits 5-lipoxygenase, the enzyme converting arachidonic acid to 5-HPETE and then leukotriene A4, thereby decreasing both LTB4 and the cysteinyl leukotrienes LTC4, LTD4, and LTD4-derived LTE4. Montelukast acts downstream as a CysLT1 receptor antagonist and does not reduce leukotriene synthesis. Zileuton leaves cyclooxygenase products untouched, and LTB4 receptor antagonism is not its mechanism.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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