By AstraZeneca

What side effects are possible with this medication?

A side effect is an unwanted response to a medication when it is taken in normal doses and cannot be anticipated. It can be mild or severe, temporary or permanent, but does not occur in everyone. The following side effects have been reported by at least 1% of people taking this medication. If you develop any of these side effects (or any other side effects not listed here) or they change in intensity, speak to your doctor or pharmacist for advice on managing them and on the risks and benefits of the medication.

  • abdominal pain
  • back pain
  • diarrhea
  • dizziness
  • fever
  • generalized pain
  • headache
  • heartburn
  • infection
  • muscle pain
  • nausea and vomiting
  • unusual weakness
Click here to learn about serious side effects that can potentially occur with any medication. These examples are provided for information purposes only and are not meant to be exhaustive. Always consult your doctor for sound medical advice specific to your particular medication and treatment.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration’s (FDA) MedWatch Adverse Event Reporting program online or by phone at 1-800-332-1088.

Are there any other precautions or warnings for this medication?

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Asthma attacks: Zafirlukast should not be used in an attempt to relieve acute asthma attacks. Have your rescue medication ready in case of an acute attack. Do not stop taking zafirlukast without consulting your doctor.

Liver problems: Zafirlukast may cause severe liver problems. It is not recommended for people with reduced liver function. If you develop jaundice (signs include yellowing of the skin or eyes), flu-like symptoms, nausea, fatigue, loss of appetite, itching, and pain on the right side of your abdomen or under the ribcage, stop taking the medication and contact your doctor immediately.

Neuropsychiatric events: Neuropsychiatric events including insomnia and depression have been reported in some people taking zafirlukast. Notify your doctor if you notice these changes. You may need to have your medication changed.

Warfarin interaction: Taking warfarin together with zafirlukast significantly increases the time it takes for blood to clot. Patients taking warfarin and zafirlukast should have their bleeding times monitored closely and have their anticoagulant dose (warfarin) adjusted accordingly.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately to talk about the benefits and risks of using this medication.

Breast-feeding: This medication passes into breast milk. If you are a breast-feeding mother and taking zafirlukast, it may affect your baby. Talk to your doctor about whether you should stop breast-feeding or stop taking this medication.

Children: The effectiveness and safety of zafirlukast have not been established for children under 5 years of age.

What other drugs could interact with this medication?

There may be an interaction between zafirlukast and any of the following:

  • aspirin
  • calcium-channel blockers
  • carbamazepine
  • cisapride
  • cyclosporine
  • dihydropyridine
  • erythromycin
  • phenytoin
  • theophylline
  • tolbutamide
  • warfarin

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

  • stop taking one of the medications,
  • change one of the medications to another,
  • change how you are taking one or both of the medications, or
  • leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

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The contents of this health site are for informational purposes only. Always seek the advice of your physician or other qualified healthcare provider regarding any questions you may have about a medical condition.

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