Zyflo is used to prevent asthma attacks and for long-term management of asthma in adults and children at least 12 years old.

Zyflo may also be used for purposes not listed in this medication guide.

Zyflo is not a fast-acting rescue medicine for asthma attacks. Seek medical attention if your breathing problems get worse quickly, or if you think your medications are not working.

Call your doctor right away if you have any changes in behavior or sleep problems.

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Zyflo tablets are usually taken 4 times a day at the same times each day, with or without food. If you cannot swallow a tablet whole, split it in half and take one half at a time.

Zyflo extended-release tablets are usually taken twice daily, within 1 hour after your morning and evening meals.

Swallow the extended-release tablet whole and do not crush, chew, or break it.

Your symptoms may not improve for several days or a few weeks. Keep using Zyflo even after you have no symptoms (a sign that the medicine is working).

Zyflo is not a fast-acting rescue medicine for asthma attacks. Seek medical attention if your breathing problems get worse quickly, or if you think your medications are not working.

Do not change your dose or stop using asthma medication without your doctor's advice.

You will need frequent blood tests to check your liver function.

Store at room temperature away from moisture, heat, and light.

You should not use Zyflo if you are allergic to it, or if you have:

• liver disease; or

• very high liver enzymes on a blood test.

Tell your doctor if you have ever had:

• liver problems, dark urine, or jaundice (yellow eyes or skin); or

• if you drink large amounts of alcohol.

Tell your doctor if you are pregnant or breastfeeding.

If you are pregnant, your name may be listed on a pregnancy registry to track the effects of zileuton on the baby.

Skip the missed dose and take your next dose at the regular time. Do not take two doses at one time.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Avoid drinking alcohol. It may increase your risk of liver damage.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Zyflo may cause serious side effects. Call your doctor at once if you have:

• worsening asthma symptoms;

• sleep problems;

• changes in behavior or sleep problems; or

• liver problems--nausea, stomach pain (upper right side), tiredness, itching, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).

Common side effects of Zyflo may include:

• upset stomach, diarrhea, nausea, or stomach pain;

• muscle aches;

• headache; or

• runny or stuffy nose, sinus pain, sneezing, sore throat.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

When you start or stop taking Zyflo, your doctor may need to adjust the doses of other medicines you use on a regular basis, especially:

• propranolol;

• theophylline; or

• warfarin, Coumadin, Jantoven.

This list is not complete. Other drugs may affect Zyflo, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.