A synthetic derivative of hydroxyurea with antiasthmatic properties. The leukotriene inhibitor zileuton blocks 5-lipoxygenase, which catalyzes the formation of leukotrienes from arachidonic acid; causes bronchodilation; decreases bronchial mucous secretion and edema; and may prevent or decrease the symptoms of asthma. OR A substance that is used to prevent asthma symptoms and that is being studied in the prevention of lung cancer. It belongs to the family of drugs called leukotriene blockers.