A patient with asthma started on zileuton returns with elevated transaminases. Monitoring is intensified. Which additional clinically important property of zileuton distinguishes it from montelukast and requires dose adjustment of co-prescribed drugs?

• A It induces CYP3A4 and reduces levels of oral contraceptives
• B It inhibits CYP2C9 and potentiates sulfonylurea hypoglycaemia
• C It inhibits CYP1A2 and raises plasma levels of theophylline and warfarin ✓
• D It has no cytochrome interactions but prolongs the QT interval

Explanation

Zileuton inhibits 5-lipoxygenase, blocking leukotriene synthesis itself, unlike montelukast which only antagonises the cysteinyl leukotriene receptor. Zileuton also inhibits CYP1A2, so theophylline, warfarin and propranolol levels rise and require monitoring or dose reduction. Hepatotoxicity with transaminase elevation is its characteristic adverse effect, necessitating liver function monitoring. Montelukast lacks meaningful cytochrome-mediated interactions of this type, which is why option C correctly separates the two drugs.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

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