Detailed Drug Information:

DRUG CLASS AND MECHANISM: Zafirlukast is an oral leukotriene receptor antagonist used for treating asthma. Leukotrienes are a group of chemicals manufactured in the body from arachidonic acid. Release of leukotrienes within the body, for example, by allergic reactions, promotes inflammation in many diseases such as asthma, a disease in which inflammation occurs in the lungs. Zafirlukast blocks the binding of leukotriene types D4 (LTD4), and E4 (LTE4). It was approved by the FDA in 1996.

PREPARATIONS: Tablets: 20mg.

STORAGE: Tablets should be stored at room temperature, between 15 and 30 °C (59-86 °F).

PRESCRIBED FOR: Zafirlukast is used in the chronic treatment of asthma. It also is effective in preventing exercise-induced asthma and in relieving the symptoms of allergic rhinitis. In the treatment of asthma, zafirlukast starts working only after 3 to 14 days of therapy. Therefore, it should not be used for treating an acute asthmatic attack in which prompt effectiveness is needed..

DOSING: Food reduces the absorption of zafirlukast. Therefore, it should be taken either 1 hour before or 2 hours after meals. It is generally taken twice daily in patients with asthma. Although data is limited, zafirlukast may be given only once daily in patients with allergic rhinitis.

DRUG INTERACTIONS: Zafirlukast inhibits the activity of cytochrome isozymes CYP 3A4 and CYP 2C9. The CYP 3A4 isozyme is responsible for metabolism of many drugs. Thus far, data in humans are very limited. In one small study, zafirlukast was shown to interact with warfarin (Coumadin), resulting in increased "thinning" of blood and a decreased ability of blood to clot. This can increase the risk of bleeding.

Until more data are available, zafirlukast should be used very cautiously in patients taking the following drugs: drugs metabolized by CYP2C9 such as amitriptyline (Elavil), diclofenac (Voltaren; Cataflam), ibuprofen (Motrin; Advil), imipramine (Tofranil), phenytoin (Dilantin), and tolbutamide (Orinase); drugs metabolized by CYP3A4 including alprazolam (Xanax), astemizole (Hismanal), carbamazepine (Tegretol), cisapride (Propulsid), cyclosporine (Neoral; Sandimmune), dihydropyridine calcium channel blockers. e.g., felodipine (Plendil), isradipine (Dynacirc), nicardipine (Cardene), nifedipine (Procardia; Adalat), nimodipine (Nimotop), and amlodipine (Norvasc); diltiazem (Cardizem; Tiazac; Dilacor), erythromycin, lovastatin (Mevacor), quinidine (Quinidex; Quinaglute), simvastatin (Zocor), triazolam (Halcion), verapamil (Calan; Isoptin; Verelan; Covera-HS).

PREGNANCY: Safe use of zafirlukast during pregnancy has not been established. Physicians may prescribe zafirlukast during pregnancy if it is felt that its benefits outweigh the potential unknown risks.

NURSING MOTHERS: Zafirlukast is secreted into breast milk and should not be used by women who breast-feed.

SIDE EFFECTS: The most common side effects of zafirlukast are headache, dizziness, abdominal pain, sore throat, and rhinitis. These can occur in between 1 in 50 and 1 in 7 patients.