indication

For the prophylaxis and chronic treatment of asthma in adults and children 12 years of age and older.

pharmacology

Zileuton is an asthma drug that differs chemically and pharmacologically from other antiasthmatic agents. It blocks leukotriene synthesis by inhibiting 5-lipoxygenase, an enzyme of the eicosanoid synthesis pathway. Current data indicates that asthma is a chronic inflammatory disorder of the airways involving the production and activity of several endogenous inflammatory mediators, including leukotrienes. Sulfido-peptide leukotrienes (LTC4, LTD4, LTE4, also known as the slow-releasing substances of anaphylaxis) and LTB4, a chemoattractant for neutrophils and eosinophils, are derived from the initial unstable product of arachidonic acid metabolism, leukotriene A4 (LTA4), and can be measured in a number of biological fluids including bronchoalveolar lavage fluid (BALF) from asthmatic patients. In humans, pretreatment with zileuton attenuated bronchoconstriction caused by cold air challenge in patients with asthma.

mechanism of action

Leukotrienes are substances that induce numerous biological effects including augmentation of neutrophil and eosinophil migration, neutrophil and monocyte aggregation, leukocyte adhesion, increased capillary permeability, and smooth muscle contraction. These effects contribute to inflammation, edema, mucus secretion, and bronchoconstriction in the airways of asthmatic patients. Zileuton relieves such symptoms through its selective inhibition of 5-lipoxygenase, the enzyme that catalyzes the formation of leukotrienes from arachidonic acid. Specifically, it inhibits leukotriene LTB4, LTC4, LTD4, and LTE4 formation. Both the R(+) and S(-) enantiomers are pharmacologically active as 5-lipoxygenase inhibitors in in vitro systems. Due to the role of leukotrienes in the pathogenesis of asthma, modulation of leukotriene formation by interruption of 5-lipoxygenase activity may reduce airway symptoms, decrease bronchial smooth muscle tone, and improve asthma control.

toxicity

The oral minimum lethal doses in mice and rats were 500-4000 and 300-1000 mg/kg in various preparations, respectively (providing greater than 3 and 9 times the systemic exposure [AUC] achieved at the maximum recommended human daily oral dose, respectively).

biotransformation

Hepatic. Zileuton and its N-dehydroxylated metabolite are oxidatively metabolized by the cytochrome P450 isoenzymes 1A2, 2C9 and 3A4.

absorption

Rapidly and almost completely absorbed. The absolute bioavailability is unknown.

half life

2.5 hours

route of elimination

Elimination of zileuton is predominantly via metabolism with a mean terminal half-life of 2.5 hours. The urinary excretion of the inactive N-dehydroxylated metabolite and unchanged zileuton each accounted for less than 0.5% of the dose.

drug interactions

Aminophylline: Zileuton increases the effect and toxicity of theophylline

Dihydroergotamine: Possible ergotism and severe ischemia with this combination

Ergotamine: Possible ergotism and severe ischemia with this combination

Oxtriphylline: Zileuton increases the effect and toxicity of theophylline

Pimozide: Increased risk of cardiotoxicity and arrhythmias

Ramelteon: Zileuton increases levels/toxicity of ramelteon

Theophylline: Zileuton may increase the therapeutic and adverse effects of theophylline by increasing its serum concentration. Monitor for changes in the therapeutic and adverse effects of theophylline if zileuton is initiated, discontinued or dose changed. Dose alterations should be considered.