5-Lipoxygenase (5-LOX) is the enzyme responsible for leukotriene synthesis. Zileuton inhibits 5-LOX, while montelukast blocks the cysteinyl leukotriene receptor CysLT1. In terms of spectrum of action, which statement is correct?

• A Montelukast blocks both CysLT1 and LTB4-mediated neutrophil chemotaxis; zileuton does not
• B Both drugs have equivalent efficacy in aspirin-exacerbated respiratory disease
• C Montelukast reduces LTB4 synthesis through feedback inhibition of 5-LOX
• D Zileuton blocks synthesis of all leukotrienes including LTB4 (neutrophil chemoattractant) and LTC4/D4/E4; montelukast blocks only CysLT1-mediated effects of LTC4/D4/E4 ✓

Explanation

Zileuton inhibits 5-lipoxygenase, the enzyme responsible for converting arachidonic acid to leukotriene A4 (LTA4). This blocks synthesis of ALL leukotrienes downstream — LTB4 (a potent neutrophil chemoattractant) as well as the cysteinyl leukotrienes (LTC4, LTD4, LTE4). Montelukast is a selective CysLT1 receptor antagonist that blocks only the effects of LTC4/D4/E4 on airways (bronchoconstriction, mucus secretion) but does not affect LTB4-mediated neutrophil recruitment. Zileuton's broader spectrum can be advantageous in ASA-exacerbated respiratory disease (AERD), but zileuton requires liver function monitoring and has drug interactions via CYP1A2 inhibition.

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

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