Zileuton is used for the maintenance treatment of asthma. Zileuton is an orally active inhibitor of 5-lipoxygenase, and thus inhibits leukotrienes (LTB4, LTC4, LTD4, and LTE4) formation. Zileuton was introduced in 1996 by Abbott Laboratories and is now marketed in two formulations by Cornerstone Therapeutics Inc. under the brand names ZYFLO and ZYFLO CR. The original immediate-release formulation of zileuton, known as ZYFLO, is taken four-times-per-day. The extended-release formulation, ZYFLO CR, is taken twice daily.