Loctril 4 mg is a chewable tablet containing Montelukast Sodium, a selective leukotriene receptor antagonist. It is primarily used for the prophylaxis and chronic treatment of asthma in patients aged 2 years and older. Additionally, Loctril is effective in relieving symptoms of allergic rhinitis, including seasonal and perennial types. The active ingredient works by inhibiting the action of leukotrienes—chemicals in the body that cause inflammation and constriction in the airways. This mechanism helps to reduce symptoms such as wheezing, shortness of breath, and nasal congestion.