Desloratadine + Montelukast is a combination of two medicines: Desloratadine and Montelukast, which treats sneezing and runny nose caused due to allergies. Desloratadine is an antiallergic which blocks the action a chemical messenger (histamine) responsible for runny nose, watery eyes and sneezing. Montelukast is a leukotriene antagonist. It works by blocking the action of another chemical messenger (leukotriene). This reduces inflammation (swelling) in the airways and nose, and improves symptoms.