Leukotriene modifiers can help control asthma symptoms by reducing inflammation and airway constriction. These medications alter the activity of leukotrienes, which drive inflammation and play a role in asthma pathology.

Leukotriene receptor blockers (or antagonists) and leukotriene synthesis blockers are two classes of modifiers.

They work differently but ultimately aim to reduce the amount of leukotrienes in the body. This is an effect that can help relieve asthma symptoms.

Read on to learn more about using leukotriene modifiers for asthma.

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People can use leukotriene modifiers to treat asthma symptoms or even prevent them from occurring. Two classes of leukotriene modifiers are available to help prevent and treat asthma symptoms: Leukotriene receptor blockers and leukotriene synthesis blockers.

Montelukast (Singulair) and zafirlukast (Accolate) are cysteinyl leukotriene receptor blockers. Zileuton (Zyflo) is a leukotriene synthesis blocker. Both drugs work on leukotrienes that the body produces from different inflammatory cells.

Receptor blockers vs. synthesis blockers

Cysteinyl leukotriene receptor blockers interfere with and prevent cysteinyl leukotrienes from binding to their receptors. Doctors prescribe these medications to treat chronic asthma. They can help reduce inflammation and vasoconstriction (narrowing of blood vessels), which can improve the following symptoms:

  • coughing
  • wheezing
  • difficulty breathing
  • chest tightness

On the other hand, zileuton works by generally blocking the production of leukotrienes. It can help reduce the following:

  • inflammation
  • mucus secretion
  • fluid buildup in the lungs
  • narrowing of the bronchioles (the small airways in the lungs)

Overall, zileuton helps to reduce asthma exacerbations and improves symptoms.

The table below summarizes the names, age ranges, and dosages (in milligrams) of leukotriene modifiers that doctors use to treat and prevent chronic asthma symptoms.

Generic nameBrand nameAgeDosage

Accolatefor adults and children aged 5 years or older• Adults and children aged 12 years and older: 20 mg twice daily
• Children between 5 and 11 years old: 10 mg twice daily
montelukastSingulairfor adults and children aged 12 months or older• Children 12–23 months old: 4 mg packet of oral granules once daily
• Children 2–5 years old: 4 mg chewable tablet or 4 mg oral granules once daily
• Children 6–14 years old: 5 mg chewable tablet once daily
• Adults and adolescents aged 15 years and older: 10 mg once daily
zileutonZyflofor adults and children aged 12 years or olderTwo 600 mg extended-release tablets twice daily

Each type of leukotriene modifier has its own specific side effects. People generally have good toleration of leukotriene receptor blockers — montelukast and zafirlukast — and these have few severe side effects.

Leukotriene receptor blockers

The following table lists the side effects of montelukast and zafirlukast.

Side effects of montelukast in childrenSide effects of montelukast in adultsSide effects of zafirlukast in adults and children aged 5 years or older
nauseafluupper respiratory tract infection
infection of the larynx or pharynx pain in bellynausea
sinus infection upset stomachvomiting
ear infectioncoughupset stomach
viral infection depression pain in the belly
aggression suicidal thoughtsgeneral unwellness (malaise)
depressiontrouble sleeping

Although zileuton works slightly differently in the body compared to montelukast and zafirlukast, it has similar side effects, such as:

  • sinus infection
  • nausea
  • throat pain

More severe side effects may include liver toxicity and neuropsychiatric effects, such as trouble sleeping and change in behavior.

Doctors prescribe leukotriene modifiers to people with chronic asthma but must respect the age ranges for each drug. For example, zafirlukast is not suitable for children under five years old, while montelukast is generally safe for children from 12 months old.

Asthma attacks

Doctors do not use either type of leukotriene modifier to treat asthma attacks. Asthma attacks occur when the smooth muscle surrounding the bronchioles constricts. This action results in significant narrowing of the bronchioles. During an asthma attack, people experience severe difficulty breathing and often describe the sensation as if someone is sitting on their chest.

Treatment for an asthma attack requires a quick-acting drug. Leukotriene modifiers are not quick-acting. Doctors may provide an action plan for people or parents of children with asthma. The action plan describes what to do during an asthma attack. Quick-acting drugs for treating asthma attacks typically come in an inhaler.


People allergic to specific active or inactive ingredients in leukotriene modifier forms should not take these drugs. Doctors will likely not prescribe montelukast to someone with severe asthma. Also, due to the presence of phenylalanine in chewable montelukast tablets, people with the genetic disease phenylketonuria cannot take them.

Zafirlukast is also not suitable for people with liver problems due to the possibility of the following:

  • risk of liver enzyme levels increasing in the blood
  • risk of acute hepatitis
  • risk of hyperbilirubinemia, another liver condition

Since zileuton is a different type of leukotriene modifier, it has different contraindications. People cannot take zileuton if they have acute liver disease or an allergy to it. Doctors may prescribe zileuton to females over 65 but are generally cautious about the increased risk of liver injury in this population.

Doctors use montelukast for preventing and treating symptoms of asthma, but it may also help to relieve certain allergy symptoms, for example, a leaky nose. For allergies, doctors usually prescribe montelukast with other medications, such as glucocorticoid nasal sprays.

Zafirlukast may also play a role in relieving allergies, but this is an off-label use. Off-label use is when a doctor prescribes a medication for a condition that the Food and Drug Administration (FDA) has not yet approved it for.

Leukotriene modifiers help treat asthma symptoms by altering the action of leukotrienes, molecules that play a role in airway inflammation and constriction.

Leukotriene receptor blockers — including montelukast and zafirlukast — and the leukotriene synthesis blocker zileuton are two types of leukotriene modifier drugs.

A doctor can determine which leukotriene modifier is the best choice for someone with asthma, and they will likely consider the person’s age, co-occurring health conditions, and side effect risks.