(682) Leukotriene Modifiers for Respiratory System Conditions

Drugs Affecting the Respiratory System: Leukotriene Modifiers

Introduction to Leukotriene Modifiers

• Class Members: Zileuton, Zafirlukast, and Montelukast.

• Role of Leukotrienes: These are potent inflammatory mediators that actively promote:

  • Constriction of smooth muscle.

  • Increased vascular permeability.

  • Recruitment of inflammatory cells to sites of inflammation.

• General Mechanisms of Action:

  • Zileuton: Inhibits the conversion of arachidonic acid to leukotrienes by blocking the enzyme $5$-lipoxygenase, which is responsible for this metabolic pathway.

  • Zafirlukast and Montelukast: Function as leukotriene receptor antagonists. They bind to and block leukotriene receptors, preventing leukotrienes from exerting their effects.

• Overall Therapeutic Effects: These drugs collectively lead to:

  • Decreased bronchoconstriction.

  • Reduced inflammatory response, consequently decreasing edema and mucus production.

• Therapeutic Indications and Limitations:

  • Considered second-line treatment for mild asthma, particularly for patients who have a contraindication to inhaled glucocorticoids.

  • Can serve as an alternative to a long-acting beta agonist when used as an add-on to an inhaled glucocorticoid, provided the patient can tolerate it.

  • Crucially, these drugs will not abort an ongoing or acute asthma attack.

• Neuropsychiatric Effects: A significant concern, especially in pediatric and adolescent patients, though less common in adults.

  • It is vital to educate parents and caregivers to immediately report any of the following symptoms to the healthcare provider:

    • Depression.

    • Suicidal ideation.

    • Insomnia.

    • Abnormal dreams.

    • Anxiety.

    • Hallucinations.

  • The occurrence of such effects may warrant discontinuation of the medication.

Specific Leukotriene Modifiers

Zileuton

• Mechanism of Action (MOA): Inhibits $5$-lipoxygenase, thereby blocking the synthesis of leukotrienes from arachidonic acid.

• Indications: Persistent asthma, for patients aged $12$ years and above.

• Dosing Considerations: Available in an extended-release form, which must be taken within $1$ hour of food.

• Adverse Effects: Strongly associated with reversible hepatitis.

  • Monitoring: Requires baseline Alanine Aminotransferase (ALT) testing prior to initiation. Liver function may warrant monitoring for the first $3$ months, and then periodically thereafter. The drug should be stopped if the patient develops symptomatic hepatitis.

• Drug Interactions:

  • Elevates the levels of both theophylline and warfarin; therefore, a reduction in the dosage of these concomitant drugs may be necessary.

  • Metabolized by the cytochrome P$450$ system. It is a substrate for CYP1A2, CYP2C9, and importantly, CYP3A4. Inducers of the CYP3A4 system can lower Zileuton levels.

  • Also acts as an inhibitor of CYP1A2, contributing to a complex profile of potential drug interactions.

Zafirlukast

• Mechanism of Action (MOA): Acts as a leukotriene receptor antagonist, blocking the binding of leukotrienes to their receptors.

• Indications: Chronic asthma, for patients aged $5$ years and above.

• Dosing Considerations: Should be taken either $1$ hour before meals or $2$ hours after meals.

• Adverse Effects:

  • Sjögren's Syndrome: Rarely associated, but can present with symptoms such as weight loss and flu-like illness.

  • Liver Injury: Although rare, liver injury is a potential adverse effect. Patients should be educated to report any signs of hepatotoxicity immediately, including jaundice, discoloration of stool and urine, fever, or abdominal pain. Discontinuation of the drug is necessary if hepatotoxicity is suspected.

• Drug Interactions:

  • Similar to Zileuton, it can elevate levels of theophylline and warfarin, necessitating dose reductions of these drugs.

  • Metabolized by the cytochrome P$450$ system. It is a substrate for CYP1A2, CYP2C9, and importantly, CYP3A4. Inducers of the CYP3A4 system can lower Zafirlukast levels.

  • Acts as an inhibitor of both CYP2C9 and CYP3A4, leading to various potential drug interactions.

Montelukast

• Mechanism of Action (MOA): Acts as a leukotriene receptor antagonist, blocking the binding of leukotrienes to their receptors.

• Indications:

  • Persistent Asthma: For patients aged $12$ years and above.

  • Allergic Rhinitis: Approved for both seasonal and perennial allergic rhinitis.

    • Seasonal allergic rhinitis: Indicated for ages $2$ years and above.

    • Perennial allergic rhinitis: Indicated for ages $6$ months and above.

    • Targets symptoms such as nasal congestion, rhinorrhea (runny nose), and ocular signs and symptoms.

  • Prevention of Exercise-Induced Bronchospasm: Approved for this purpose, but it is important to remember that it does not abort an ongoing attack.

• Dosing Considerations: Can be administered regardless of food intake. An advantage is that the dosing regimen is generally the same for both allergic rhinitis and asthma indications.

• Comparison to Other Treatments: For allergic rhinitis, its effects are considered limited compared to intranasal steroids, which are typically regarded as superior. Montelukast is therefore often reserved as a second-line option for allergic rhinitis, particularly when there is a contraindication to steroid use.

• Drug Interactions: Metabolized by the cytochrome P$450$ system. It is a substrate for CYP2C9 and, importantly, CYP3A4, which suggests a potential for numerous drug interactions.