Zafirlukast (Oral)

Zafirlukast is a medication used as a preventative for symptoms of asthma by reducing inflammation of the respiratory system.


Zafirlukast is prescribed to treat chronic asthma and sometimes exercise-induced breathing difficulties. In rare instances, it can also be used to treat other breathing conditions, such as hay fever.

Zafirlukast is usually taken orally in tablet form twice daily. It is a leukotriene receptor antagonist and works by reducing inflammation. This inflammation is caused by the binding of leukotrienes in your body. Zafirlukast prevents this chemical binding and so works to stop the cause of asthma symptoms.

The medication is intended for adults and children over 12 and is only prescribed to infants in rare circumstances.

It is not an effective treatment for asthma attacks but is shown to reduce the number of attacks. In this sense, it is a preventative medication. Zafirlukast is often prescribed along with steroids and a bronchodilator inhaler for patients suffering from asthma. If you experience an asthma attack, use your inhaler, rather than Zafirlukast.

It is advisable to inform your doctor if you are pregnant or breastfeeding before taking Zafirlukast. No research has shown a consistently negative effect of the drug on babies or on fetuses, however, there is not a consensus on this and your personal physician will help you weigh up the risks for your situation.

Once you have begun taking Zafirlukast, you should notice an improvement in your asthma symptoms fairly soon, but it normally takes one to two weeks before experiencing the full benefits.

If you are allergic to Zafirlukast or any of its ingredients, you should inform your doctor when the drug is prescribed. You should also inform your doctor if you are taking any other medications or suffering from any other illnesses.

To gain the full advantages of this medication, always take it exactly as your doctor instructs. You should keep taking the medication even when feeling well. For the best results, try to take your medication at the same time each day.

The appearance of your Zafirlukast tablets may vary and the medication may also be supplied under a different brand name but usually, the tablets are in a white, round film coating, with surface markings to indicate the dosage.

Non-medical ingredients in the tablets frequently include:

  • croscarmellose sodium
  • hypromellose
  • lactose monohydrate
  • magnesium stearate
  • microcrystalline cellulose
  • povidone
  • titanium dioxide

If you are allergic to any of these ingredients, inform your doctor before starting your Zafirlukast doses.

Conditions treated

  • chronic asthma
  • exercise induced breathing problems
  • allergic rhinitis
  • hay fever

Type of medicine

  • Leukotriene receptor antagonist (LTRA)

Side Effects

While severe side effects are relatively uncommon with Zafirlukast, there are a number of possible side effects noted in patients taking this medication. These tend to be mild in the vast majority of cases.

Side effects of any medication are more likely when you first begin taking them. Most of these lessen as your body adjusts and do not require medical intervention or for you to stop your medication.

Side effects can be permanent or temporary and mild or severe. Persistent and severe symptoms that occur in conjunction with taking your medication may be cause for concern. In these cases, you should consult your doctor immediately.

The following are some known side effects of Zafirlukast in some patients:

  • headaches
  • nausea
  • sore throat
  • malaise
  • disrupted sleep
  • mild respiratory infection

Your doctor will have deemed these as acceptable side effects by prescribing Zafirlukast to you, but should symptoms worsen or persist you should visit your doctor to check for adverse risks to your health.

Some less usual side effects can include:

  • coughing
  • fever or chills
  • lower back pain
  • pain or difficulty urinating

Some rare side effects can include:

  • clay-colored stool
  • dark urine
  • diarrhea
  • dizziness
  • itching
  • unpleasant breath odor
  • tiredness or weakness

Should you experience any mild side effects that are commonly associated with Zafirlukast, continue to take your medication unless instructed otherwise by your doctor.

While some side effects are to be expected, if you experience any of the following symptoms while taking Zafirlukast consult a doctor immediately. These are reported in less than 1% of patients and are a sign of adverse health risks:

  • flu-like symptoms
  • difficulty breathing or swallowing
  • pain, burning, numbness or tingling in your extremities
  • rash
  • excessive tiredness
  • stomach pain
  • vasculitis
  • eosinophilia
  • agitation
  • aggression
  • hallucinations
  • abnormal dreams
  • depression
  • suicidal thoughts
  • vomiting blood
  • coughing blood
  • swelling of the extremities
  • chest pain

Very few patients experience an allergic reaction to Zafirlukast, but if you experience any symptoms consistent with an allergic reaction, please seek medical assistance straight away.

You should also consult a healthcare professional quickly if you experience side effects not usually associated with this medication.

In extremely rare cases, Zafirlukast is associated with serious liver disease. This can be fatal if left untreated but when detected early, damage can often be reversed by stopping the medication. If you experience any symptoms that could be a sign of liver problems, you should seek medical assistance. Symptoms can include persistent nausea and vomiting, loss of appetite, abdominal pain and yellowing of the eyes and/or skin.

In some cases, Zafirlukast has also been found to affect patients' mood and mental state. If this takes place after starting the medication, tell your doctor and if you have a history of mental health issues inform your doctor before you begin taking Zafirlukast.


You should always take any medication exactly as instructed. Failure to take Zafirlukast in the manner instructed by your doctor can increase the risk of side effects, drug interactions or reduce the effectiveness of the medication.

If your doctor's instructions are different from the instructions on your medication bottle, contact your healthcare provider to clarify dosage and instructions for taking the medication.

If Zafirlukast does not seem to be working, do not increase your dose. Never increase or decrease your dose unless advised by your doctor. Zafirlukast is a preventative medication for asthma and takes several treatments before becoming effective.

Always prioritize your doctor's dosage instructions over the manufacturer's instructions, as the former will be tailored to your medical history and needs.

The dosage of Zafirlukast may be different for any patients, however, the standard dose is usually in tablet form and consists of:

  • 20mg twice daily for adults and children over 12 years of age
  • 10mg twice daily for children aged five to 11
  • Children under five are rarely prescribed this drug and, in these rare cases, the dose must be determined by your doctor.

Zafirlukast should be taken on an empty stomach, ideally one hour before eating or at least two hours after eating. It is usually prescribed to be taken twice daily.

If you miss a dose of Zafirlukast, take your medication as soon as possible but remember to adhere to the requirement of consuming your pills on an empty stomach. If it is nearly time for your next dose, by the time you remember the missed dose, skip the missed dose. Never take twice the amount prescribed at once to cover a missed dose. Doubling up on doses can lead to increased side effects or even overdose.

Drug interactions

When taking any form of medication, there are substantial risks of negative drug interactions if you are taking any other drug treatments. This can range in severity from merely rendering one or both of the medications ineffective or to perform sub-optimally, to having adverse health effects.

It is vital to consult your physician or contact a healthcare professional if you are taking other medications. They can then advise you accordingly. It may be that you can still take all your medications but must alter your dosage or the time at which you take your medication.

Negative drug interactions can potentially take place with any medications, whether it is a specific prescription, over the counter medications, herbal remedies or even vitamin supplements. You should, therefore, always check with a healthcare provider if you are in any doubt over the medication combinations you are taking.

Even if you are able to take all of your medications with Zafirlukast, there is the potential for drug interactions to result in additional or more severe side effects.

Be aware that some medication can alter the way your body removes Zafirlukast from your system. Zafirlukast may also slow down the removal of other drugs from your system.

Below is a non-exhaustive list of drugs that are known to negatively interact with Zafirlukast. Note this is not a complete list and there are other medications which could have a negative interaction with Zafirlukast.

If you are taking any of the following medications, it is imperative that you inform your medical provider before taking any of your scheduled doses:

  • Erythromycin
  • Warfarin
  • Strong CYP1A2 Inhibitors/Pirfenidone
  • Strong CYP1A2 Inhibitors/Ropivacaine
  • Selected CYP2C9 Inhibitors/Selected NSAIDS
  • Teriflunomide
  • Subsys (fentanyl)
  • Sublimaze (fentanyl)
  • Pimozide
  • Orap (pimozide)
  • Orlaam (levomethadyl acetate)
  • Onsolis (fentanyl)
  • Mipomersen
  • Lomitapide
  • Levomethadyl acetate
  • Leflunomide
  • Lazanda (fentanyl)
  • Kynamro (mipomersen)
  • Juxtapid (lomitapide)
  • Ionsys (fentanyl)
  • Innovar (droperidol / fentanyl)
  • Halofantrine
  • Halfan (halofantrine)
  • Fentora (fentanyl)
  • Fentanyl / ropivacaine
  • Fentanyl Transdermal System (fentanyl)
  • Fentanyl
  • Duragesic (fentanyl)
  • Droperidol / fentanyl
  • Bupivacaine / fentanyl
  • Aubagio (teriflunomide)
  • Arava (leflunomide)
  • Actiq (fentanyl)
  • Abstral (fentanyl)
  • Zafirlukast/Selected Anticoagulants (VIT K Antagonists)

It is also advisable to inform your doctor if you regularly smoke, consume caffeine, alcohol or any recreational drugs before taking this medication.

In addition to drug interactions, Zafirlukast is known to cause elevations of liver enzymes, therefore this medication is contraindicated for those with hepatic impairment. If you suffer from a liver disease, you should not take Zafirlukast unless stated otherwise by your doctor.


Patients should be aware that, while Zafirlukast is prescribed as a treatment for asthma, it is not a bronchodilator and is not used to treat sudden asthma attacks. The medication does not take immediate effect and therefore is unsuited to treating asthma attacks. It is intended as a prevention of asthma attacks.

In very rare cases Zafirlukast is associated with liver disease and severe to life-threatening instances of hepatic failure.

This risk may mean that doctors will want to run liver function testing before prescribing Zafirlukast and/or at intervals during your treatment.

It is believed that early detection can help reduce liver damage caused by Zafirlukast in these rare cases. Removal of the medication, following the early detection of liver problems, often leads to a better recovery.

If you are taking Zafirlukast, always be on the lookout for symptoms that may be an indication of liver dysfunction.

This may include the following side effects:

  • jaundice
  • anorexia
  • lethargy
  • abdominal pain in your upper right quadrant
  • fatigue
  • pruritus
  • persistent nausea
  • persistent vomiting

If your doctor suspects liver dysfunction, Zafirlukast should be stopped immediately.

In addition to hepatic failure, in rare cases, Zafirlukast is also associated with eosinophilic conditions. This can include vasculitis or eosinophilic pneumonia. Severe or worsening pulmonary symptoms are indicative of these conditions, as are vasculitis rashes, neuropathy and cardiac issues.


Zafirlukast should be stored at room temperature, ideally at 68°F to 77°F and kept in its medication bottle with the lid tightly closed.

Ensure Zafirlukast is kept dry, away from any risk of moisture, out of direct sunlight and avoid excessive heat or freezing temperatures. We do not recommend keeping Zafirlukast in a bathroom or kitchen where heat and moisture build-up is a substantial risk.

Always keep any medication in a safe location, away from the reach of children. Not all prescribed medications have a childproof cap. If a child accidentally ingests Zafirlukast, you should seek medical attention for them straightaway.

Do not keep medication if it is no longer needed or if it is past its expiration date. If you wish to dispose of your medication, never flush it down the toilet or pour it down a drain. To dispose of any unneeded or outdated medication, please contact a healthcare professional. They will instruct you on how to properly dispose of any medication you will not be using.


Zafirlukast has been proven highly effective in lessening the symptoms of asthma. By reducing inflammation of the airways, it decreases wheezing, breathlessness and tight chest sensations to aid normal breathing. When taking the appropriate dose, most patients see a marked improvement in breathing quality and a reduction in the number and severity of asthma attacks.

While there are some risks associated with taking Zafirlukast, these are rare and can usually be prevented by a healthy, open dialogue with your doctor.

Always try to divulge as much information as possible regarding your medical history, allergies, pregnancy status, other medications, addictions, dietary requirements and any other factors that could potentially affect this medication or alter its effect on your health.

If you are unaware which information is pertinent, talk openly with your doctor and ask questions.

Last Reviewed:
December 23, 2017
Last Updated:
April 05, 2018
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