Jan 14, Singulair is also used to treat symptoms of year-round (perennial) allergies in adults and children who are at least 6 months old. It is also used. Allergic Rhinitis. SINGULAIR is indicated for the relief of symptoms of seasonal allergic rhinitis in patients 2 years of age and older and perennial allergic rhinitis . May 13, Singulair (montelukast) and Xyzal (levocetirizine dihydrochloride) are used to treat allergic rhinitis. According to the package insert, Singulair please click for source taken once daily. A: Inhibition allergie leukotrienes, fatty compounds produced by the immune system that cause inflammation, potentially plays a role in the treatment of alllergies and other allergic conditions such as allergic rhinitis, atopic dermatitis, and chronic urticaria. Respir Care. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Consult your doctor or healthcare provider for specific recommendations. Monthly newsletter. Related: Hay fever. Take the missed dose as soon as you remember. There were no clinical trials in patients with asthma to compare the effectiveness of Singulair when used in the morning compared to the evening.