Easy-to-read patient leaflet for Zileuton Extended-Release Tablets. Includes indications, proper use, special instructions, precautions, and possible side effects. Includes indications, proper use, special instructions, precautions, and possible side effects.. Although the 600 mg immediate release tablet (Zyflo) and extended release formulation of zileuton are still available (Zyflo CR), the 300 mg immediate release tablet was withdrawn from the U.S. market on February 12, 2008.. Zileuton is an orally active inhibitor of 5-lipoxygenase, the enzyme that catalyzes the formation of leukotrienes from arachidonic acid. Zileuton has the chemical name (±)-1-(1-Benzo[b]thien-2-ylethyl)-1-hydroxyurea and the following chemical structure:. Zileuton tablets What is this medicine? ZILEUTON (zye LOO ton) is used to treat asthma. It helps to decrease the symptoms of asthma. Do not use for an acute asthma attack. How should I use this medicine? Take this medicine by mouth with a glass of water. Follow the directions on your…. Zileuton Extended-Release Tablets is a leukotriene synthesis inhibitor indicated for the prophylaxis and chronic treatment of asthma in adults and children 12 years of age and older.1. Zyflo™ Filmtab (zileuton tablet) manufacturer's package insert, Abbott Laboratories, USA. Google Scholar In addition, close monitoring of theophylline concentrations is warranted..