Singulair (generic name: montelukast) is a widely prescribed oral medication used for the management of chronic respiratory and allergic conditions. It is a maintenance treatment that helps to control symptoms associated with inflammation in the airways and nasal passages. The drug is often used to improve breathing and reduce the impact of environmental triggers.
Singulair’s Drug Classification
Singulair is not an antihistamine, despite being commonly used to treat allergy symptoms. Antihistamines work by blocking the effects of histamine, a chemical mediator that causes immediate allergic reactions like sneezing, itching, and a runny nose. Singulair belongs to a separate class of drugs known as leukotriene receptor antagonists (LTRAs) or leukotriene modifiers. This classification means its primary function is to interfere with the actions of leukotrienes, which are powerful inflammatory molecules.
Understanding Leukotrienes
Leukotrienes are lipid mediators, or signaling molecules, derived from the metabolism of arachidonic acid in the body. These substances are produced and released by various inflammatory cells, including mast cells, eosinophils, and macrophages, particularly in the respiratory tract. Their release is triggered when the body encounters an allergen, such as pollen or dust mites, or an irritant.
The cysteinyl leukotrienes (LTC4, LTD4, and LTE4) are the most potent of these molecules in the context of allergic disease. When released, they contribute significantly to the symptoms of asthma and allergic rhinitis. They cause the smooth muscles surrounding the airways to contract, leading to bronchoconstriction and a narrowing of the air passages.
Leukotrienes also increase the permeability of blood vessels, which leads to swelling and edema in the airway lining. Furthermore, they stimulate the production of thick mucus, which can further obstruct airflow.
Mechanism of Action
Singulair works by acting as a highly selective antagonist at a specific site in the body’s inflammatory response system. The drug’s active ingredient, montelukast, binds with high affinity to the cysteinyl leukotriene type-1 (CysLT1) receptor. This receptor is found on various cells throughout the airways, including smooth muscle cells, macrophages, and eosinophils.
By occupying the CysLT1 receptor, montelukast physically prevents the inflammatory leukotrienes (LTC4, LTD4, and LTE4) from attaching to it. This action disrupts the signaling cascade that normally leads to airway inflammation and constriction.
Blocking the CysLT1 receptor reduces the three major physiological effects caused by leukotrienes. It prevents the smooth muscle from contracting, which reduces bronchoconstriction and improves airflow. It decreases the vascular permeability, lessening the swelling and edema in the airways and nasal passages. This mechanism also leads to a reduction in mucus secretion, helping to clear the respiratory tract.
Conditions Treated by Singulair
Singulair is approved for several specific indications that involve chronic inflammation driven by the leukotriene pathway. The primary use is for the long-term prophylaxis and treatment of asthma in both adults and children. It is important to note that Singulair is a maintenance drug and is not intended for the immediate relief of an acute asthma attack.
The medication is also widely used to relieve the symptoms of allergic rhinitis, which includes both seasonal (hay fever) and perennial (year-round) allergies. For patients with exercise-induced bronchoconstriction (EIB), Singulair is used as a preventive measure when taken before physical activity. The drug is often used as a complementary therapy alongside inhaled corticosteroids when they alone do not provide sufficient asthma control.