Points of comparison	Zafirlukast (Accolate)	Zileuton (Zyflo)
Mechanism of action	Blocks the cysteinyl leukotrienes LTD4 and LTE4 at the CsyLT1 receptor	Selectively and reversibly inhibits the 5-lipoxygenase pathway
Adverse effects	Generally well tolerated	Generally well tolerated
	Side effects include headache, infection, nausea, diarrhea	Side effects include dyspepsia, headache, infections, asthma exacerbations
		Elevated liver transaminase levels (usually transient; however, liver function tests should be performed monthly for the first three months of therapy and then every two to three months for the first year of treatment)
Drug interactions	Interacts with drugs metabolized by cytochrome P450 enzymes 3A4 (e.g., phenytoin [Dilantin], carbamazepine [Tegretol]) and 2C9 (e.g., cisapride [Propulsid], astemizole [Hismanal], dihydropyridine calcium channel blockers)	May interact with drugs metabolized by cytochrome P450 enzymes 1A2, 3A4 and 2C9 Reported interactions with theophylline, warfarin and propranolol (Inderal)
	Increases the effect of warfarin (Coumadin)
	Plasma level decreased by erythromycin and theophylline
	Plasma level raised by aspirin
Contraindications	Breast feeding	Active liver disease
		Breast feeding
Precautions	Should be used with caution in elderly patients and patients with hepatic disease
Use in pregnancy	Category B	Not recommended
Dosage	20 mg twice daily, taken one hour before or two hours after meals	600 mg orally, taken four times daily with or without food
Cost*	$56	$83