Leukotriene modifiers are a relatively new class of drugs designed to prevent asthma and allergic reactions before they occur. They target leukotrienes, which are chemicals that inflame the lining of airways and cause symptoms such as wheezing and shortness of breath.

These drugs are taken orally, in pill or granule form, one to four times daily to prevent the symptoms of chronic and mild-to-moderate persistent asthma. They are a long-term strategy and are not designed to treat an asthma attack once it has begun.

Leukotriene modifiers may be effective in preventing symptoms of hay fever (allergic rhinitis) in some people, though they have not been as widely used to treat that condition. As with asthma, these medications are taken daily to prevent the onset of hay fever symptoms, not to relieve symptoms once they have started. Research into other potential uses for leukotriene modifiers, including the prevention of other forms of allergic symptoms (such as hives), is ongoing.

Patients with liver disease and those taking anticoagulants (medications that reduce the ability of blood to form clots) are among those who may need close monitoring while taking leukotriene modifiers.

Inflammation is a key characteristic of asthma, and leukotrienes function as chemical mediators (a chemical that acts as a messenger in the body) in the inflammation process.

They are byproducts of arachidonic acid, an essential fatty acid found in the outer membranes of mast cells in the body. When activated, leukotrienes constrict the muscles surrounding the airways (bronchospasm) and cause the production of excess mucus, which can clog the airways (airway wall edema).

In addition, leukotrienes attract white blood cells called eosinophils, which also release some of the major chemical mediators involved in bronchospasm. As a result, the airways swell and fill with mucus, reducing air flow.

Leukotriene modifiers (also known as leukotriene antagonists) are a relatively new class of drugs designed to prevent asthma and allergic reactions before they occur. They work by blocking the effects of leukotrienes, the chemicals involved in triggering asthma- and allergy-related symptoms.

Leukotriene modifiers work by either inhibiting leukotriene production or preventing leukotrienes from binding to cellular receptors, the cell components that combine with a drug, hormone or chemical mediator to alter the function of a cell. During an asthma attack, immunoglobulin E (IgE) destabilizes mast cells in the airway. When this happens, the mast cells release a group of chemicals – including histamines, prostaglandins and leukotrienes – that act as powerful bronchoconstrictors, narrowing airways and making breathing more difficult.

Leukotriene modifiers help short-circuit the process by targeting leukotrienes, which have a constricting effect that is 1,000 times more powerful than histamines and prostaglandins. They block the primary binding site on a cell membrane where leukotrienes bond. Blocking these cell receptors prevents the production of two of the three most powerful leukotriene bronchoconstrictors.

By shutting down the work of leukotrienes, leukotriene modifiers decrease inflammation and relax the smooth muscle around the bronchi. This prevents the body from going into an allergic response and keeps a person’s airways open and clear.

Leukotriene modifiers now in common use include:

Leukotriene modifiers can be taken in pill, chewable-tablet or granule form. These pills are taken one to four times daily, depending on which medication is used. Individuals who have been prescribed leukotriene modifiers should take the medication as directed by their physician, even when they are feeling well.

Leukotriene modifiers sometimes are prescribed to work in tandem with other asthma drugs. In some cases, patients with mild-to-moderate asthma who take leukotriene modifiers are able to reduce their reliance on other asthma drugs such as beta 2 agonists (short-acting bronchodilators that relax smooth muscle in the airways) and corticosteroids (anti-inflammatory drugs used to treat allergies and asthma). By reducing the frequency or doses of such medications, the risk of potentially serious side effects is also reduced.

Leukotriene modifiers may take several weeks to begin working, and in some people they are not effective at all. Patients taking leukotriene modifiers should consult their physician if their symptoms worsen or if they need to increase the use of their rescue medications.

Leukotriene modifiers are primarily used in the treatment of asthma for the purpose of preventing asthma attacks. The drugs may be used in combination with other therapies. Some types may also be used in the prevention of allergic reactions for non-asthmatics.

Asthma-related conditions for which leukotriene modifiers may be prescribed include:

• Moderate persistent asthma. Symptoms occurring once each day and more than one night a week.
  
  
• Mild persistent asthma. Symptoms occurring more than two times a week during the day and more than two times each month at night.

Physicians are still determining which patients are most likely to benefit from the use of leukotriene modifiers. However, these medications appear to be particularly effective in patients who suffer from aspirin-sensitive asthma, a condition in which a patient suffers a severe asthma attack after taking aspirin. Leukotriene modifiers also have been effective in patients whose asthma is triggered by exercise or allergies. There is some evidence that leukotriene modifiers may be effective in treating cases of severe adult asthma.

Leukotriene modifiers are designed to be taken daily to prevent asthma attacks before they occur. They are not bronchodilators and should not be used to treat asthma attacks once they have begun. Those who are unable to control asthma symptoms without increasing their dosage from the prescribed amount should contact their physician immediately, as this may indicate an impending asthma attack.

Some leukotriene modifiers have been approved in the United States to prevent the itching, sneezing and nasal congestion associated with seasonal and perennial (year-round) hay fever (allergic rhinitis). Some studies have indicated that leukotriene modifiers may be more effective when combined with antihistamines, thereby shutting down two major chemicals in airway constriction, histamines and leukotrienes.

It should be noted that leukotriene modifiers have not been found to be as effective as inhaled corticosteroids, and that there is not yet a body of evidence to conclusively state that leukotriene modifiers are an effective means of treating allergic rhinitis by themselves.

Other conditions for which leukotriene modifiers may be prescribed include:

• Respiratory syncytial virus (RSV), the chief cause of lower respiratory tract infections in children. Leukotriene modifiers may help by blocking the leukotrienes that act as mediators in the lingering wheezing and other asthma-like symptoms that follow a bout of RSV.
  
  
• Hives (red, swollen patches of skin). Leukotriene modifiers may be used for some patients with chronic, difficult-to-treat hives.
  
  

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Patients should not take leukotriene modifiers if they have been diagnosed with any of the following conditions:

• Drug allergies. Patients who are allergic to a leukotriene modifier, or any of its ingredients, should not take the drug. Patients should also notify their physicians if they are allergic to any other drugs.
  
  
• Liver disease. Leukotriene modifiers are removed from the body through the liver. Certain liver diseases may result in too much of this medication building up in the body, increasing the risk of side effects and/or overdose. Liver failure has also occurred in patients taking leukotriene modifiers. Those with a history of medical problems related to the liver should be monitored by a physician to ensure there is no increase in liver enzyme levels in the blood.
  
  
• Phenylketonuria (PKU). A condition in which the body is not able to convert the amino acid phenylalanine into tyrosine due to a defective enzyme. One type of leukotriene modifier (montelukast sodium chewable tablets) contains phenylalanine, which patients with phenylketonuria should not ingest.
  
  
• Blood-clotting disorders. Patients with these conditions may take anticoagulants which, when combined with leukotriene modifiers, can cause an increase in bleeding.
  
  
• Pregnancy. Leukotriene modifier use during pregnancy may not be advised.

A person should seek immediate medical attention if they experience any of the following while taking leukotriene modifiers:

• Rash or unexplained open sores or bruising
  
  
• Numbness, tingling or pain
  
  
• Worsening respiratory symptoms
  
  
• Symptoms of an allergic reaction (e.g., difficulty breathing, tightening of the throat, hives, swelling of the lips, tongue or face)

A physician should be informed if a person experiences less serious side effects of leukotriene modifiers, such as:

• Dizziness
  
  
• Headache
  
  
• Infection (e.g., ear infection, upper or lower respiratory infection)
  
  
• Joint pain (arthralgia)
  
  
• Abdominal pain or dyspepsia (painful digestion)
  
  
• Flatulence, constipation or diarrhea
  
  
• Severe itching (pruritus)
  
  
• Nausea or vomiting
  
  
• Back pain, chest pain, neck pain and rigidity or dental pain
  
  
• Muscle tenderness (myalgia) or weakness (asthenia)
  
  
• Cold-like symptoms (e.g., fever, nasal congestion, cough, sore throat)
  
  
• Fatigue or prolonged drowsiness (somnolence)
  
  
• Insomnia
  
  
• Nervousness
  
  
• Malaise (general ill feeling)
  
  
• Vaginal inflammation
  
  
• Frequent urination
  
  
• Swelling or redness around the eyes
  
  
• Heartburn
  
  
• Swollen lymph nodes (small, kidney-shaped organs of lymphoid tissue found in clusters in the neck, groin, armpit, abdominal organs and other regions of the body)

Patients experiencing these side effects should not stop taking the drug unless instructed to by a physician.

In rare cases, hepatic (liver) dysfunction may develop as a result of taking zafirlukast. Signs and symptoms of hepatic dysfunction include:

• Pain in the right, upper section of the abdomen
• Nausea
• Fatigue
• Lethargy
• Pruritus
• Jaundice
• Flu-like symptoms
• Loss of appetite

Patients who suspect hepatic dysfunction should contact their physician immediately.

There is also some evidence that montelukast sodium may cause rare cases of hepatitis and liver injury in some individuals. Patients at risk for these conditions may want to discuss this risk with their physician prior to using this drug.

A few years ago, there were concerns that use of leukotriene modifiers might lead to Churg-Strauss syndrome, which causes inflammation of the blood vessels, particularly in the lungs. However, a later review found no connection between the drugs and Churg-Strauss syndrome.

Patients using leukotriene modifiers should consult their physicians before taking any additional prescriptions, over-the-counter medications, nutritional supplements or herbal medications.

Of particular concern to individuals taking leukotriene modifiers are:

• Antibiotics. Medications that kill or slow the growth of bacteria. These drugs may decrease the effectiveness of leukotriene modifiers.
  
  
• Beta blockers. Medications that reduce the workload of the heart and lower blood pressure. They are commonly used to treat high blood pressure, angina or heart failure. These drugs may impact the effectiveness of leukotriene modifiers.
  
  
• Aspirin and aspirin-containing products. Leukotriene modifiers may increase the side effects of these medicines.
  
  
• Phenobarbital. A barbiturate, sedative and anticonvulsant used in the treatment of insomnia, epilepsy, anxiety and other conditions. Dosage adjustment or special monitoring of these drugs may be necessary for those taking leukotriene modifiers.
  
  
• Anticoagulants. Medications that inhibit the formation of blood clots. Patients taking anticoagulants in combination with leukotriene modifiers are at a greater risk to develop bleeding and may require closer monitoring by a physician.
  
  
• Grapefruit juice. Patients taking leukotriene modifiers may be advised by their physicians to avoid drinking grapefruit juice. Drinking grapefruit juice can lead to a buildup of certain medications in the body, increasing the risk of side effects.
  
  
• Alcohol. Patients should not drink alcohol while taking leukotriene modifiers because the combination can damage the liver.

Those who are taking other prescribed asthma drugs should continue to do so at the recommended doses unless their physician suggests otherwise.

There is limited experience of human overdose with leukotriene modifiers. The medications have a good safety record in situations where they have been prescribed. Overdose symptoms may be similar to, but more severe than, typical side effects associated with the use of leukotriene modifiers.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians. Patients may wish to ask their doctors the following questions about leukotriene modifiers:

1. Why are you recommending that I take this drug?
   
   
2. Can you explain to me how leukotriene modifiers work?
   
   
3. How and when should I take this drug?
   
   
4. What should I do if I miss a dose?
   
   
5. How will I know if the drug is working?
   
   
6. What will be the next step if the drug fails to prevent my symptoms?
   
   
7. How will this drug affect my current medical conditions other than asthma/hay fever?
   
   
8. How will this drug interact with other medications I am currently taking?
   
   
9. What side effects may I develop from taking this drug?
   
   
10. For what side effects should I seek medical attention?
    
    
11. I am thinking about becoming pregnant. Can I continue to take this drug when I am pregnant?