FEXOSTAR-M TAB used in the treatment of sneezing and runny nose due to allergies. Montelukast is a leukotriene antagonist. It works by blocking the action of a chemical messenger called leukotriene. This reduces inflammation (swelling) in the airways and nose and improves symptoms. Fexofenadine is an antiallergic which blocks the action of another chemical messenger (histamine) responsible for runny nose, watery eyes and sneezing.