In the U.S.—

• Antiasthmatic, leukotriene receptor antagonist

Zafirlukast (za-FIR-loo-kast) is used by patients with mild-to-moderate asthma to decrease the symptoms of asthma and the number of acute asthma attacks. However, this medicine should not be used to relieve an asthma attack that has already started.

This medicine is available only with your doctor's prescription, in the following dosage form:

Oral
• Tablets (U.S.)

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For zafirlukast, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to zafirlukast.

Pregnancy—Zafirlukast has not been studied in pregnant women. Studies in animals have shown that this medicine causes problems only when given in doses many times higher than the usual human dose.

Breast-feeding—Zafirlukast passes into breast milk and may cause unwanted effects in nursing babies. Breast-feeding is not recommended while you are taking zafirlukast.

Children—Studies on this medicine have been done only in adult patients and there is no specific information comparing use of zafirlukast in children up to 7 years of age with use in other age groups.

Older adults—In studies, mild to moderate respiratory tract infections were more likely to occur in patients 55 years of age or older taking zafirlukast. It is not known whether these infections were caused by taking zafirlukast or by other factors.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking zafirlukast, it is especially important that your health care professional know if you are taking any of the following:

• Warfarin (e.g., Coumadin)—Zafirlukast may increase the effects of this medicine

Zafirlukast is used to prevent asthma attacks. It is not used to relieve an attack that has already started. For relief of an asthma attack that has already started, you should use another medicine. If you do not have another medicine to use for an attack or if you have any questions about this, check with your health care professional.

Food may change the amount of zafirlukast that is absorbed. For this reason, it should be taken on an empty stomach, 1 hour before or 2 hours after a meal.

Dosing—

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of zafirlukast. If your dose is different, do not change it unless your doctor tells you to do so.

• For oral dosage form (tablets):
  • For asthma:
    • Adults and children 12 years of age and older—20 milligrams (mg) two times a day, on an empty stomach, at least 1 hour before or 2 hours after meals.
    • Children between 7 and 11 years of age—10 milligrams two times a day, on an empty stomach, at least 1 hour before or 2 hours after meals.
    • Children up to 7 years of age—Use and dose must be determined by your doctor.

Missed dose—

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

To work properly, zafirlukast must be taken every day at regularly spaced times, even if your asthma seems better.

You may be taking other medicines for asthma along with zafirlukast. Do not stop taking or reduce the dose of the other medicines, even if your asthma seems better, unless you are told to do so by your doctor .

Along with its needed effects, a medicine may cause some unwanted effects. The following side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• Less common
  • Headache;  nausea