Wikipedia
An antileukotriene is a drug which functions as a leukotriene-related enzyme inhibitor ( arachidonate 5-lipoxygenase) or leukotriene receptor antagonist ( cysteinyl leukotriene receptors) and consequently opposes the function of these inflammatory mediators; leukotrienes are produced by the immune system and serve to promote bronchoconstriction, inflammation, microvascular permeability, and mucus secretion in asthma and COPD. Leukotriene receptor antagonists are sometimes colloquially referred to as leukasts.
Leukotriene receptor antagonists, such as montelukast, zafirlukast, and pranlukast, and 5-lipoxygenase inhibitors, like zileuton and hypericum perforatum, can be used to treat these diseases. They are less effective than corticosteroids for treating asthma, but more effective for treating certain mast cell disorders.